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Phils Tropical Weather Blog Just another WordPress.com site Skip to content HomeAboutImagesLinks Older posts Tropical Storm Isaac moving over Hispaniola and Cuba, heading for the Gulf of Mexico with a US landfalllooming Posted on August 25, 2012 | Leave a comment

Tropical Activity For August 25th, 2012

Things continue to remain busy in the Atlantic basin as we have reached the latter half of August. Tropical Storm Isaac (which developed from Invest 94L) is making landfall along the coastline of Haiti, and will be dancing around both Hispaniola and Cuba over the next 24 hours, but seems poised to have a US impact. Meanwhile, Tropical Storm Joyce has degenerated into a trough of low pressure in the Central Atlantic, while there is a new invest (97L) which has emerged off the African coast. Neither of these storms has a substancial threat to develop over the next 24 hours, so my focus will be rightfully on Isaac.

Tropical Storm Isaac

Visible / Infrared Animation of Tropical Storm Isaac

Isaac has been on a tough road the last few days. After becoming a tropical depression earlier in the week, the storm fought bouts of dry air, which prevented the mid-level circulation from aligning with the low-level circulation, hampering development. However, earlier today, the presentation improved substantially as the low and mid-level centers finally aligned. This evening, the convection has organized over the circulation center. As Isaac continues to move further to the northwest, it will interact with the high terrain of Hispaniola and Cuba, but will eventually emerge back over the warm waters south of Florida. Where does Isaac look to be going next, and where in the United States will the impacts be felt? Read below for all the details!

500 hPa forecast comparison for both the ECMWF and GFS. Plotted are heights (white contours), and vorticity (color shading).

Lets first talk about track. Animated above are the 24-96 hour 500 hPa heights and vorticity from both the ECMWF and GFS, two trusted models with a history of accurate tropical cyclone forecasts. Note that early on in the forecast, we have a weakness in place between two mid-level ridges. This is what is causing the NW movement through Haiti currently. However, as this weakness fills back in, the system should bend more to the west-northwest, rounding the northern edge of Cuba. The GFS is a touch faster, but generally both the ECMWF and GFS are in good agreement here. The ridge holds for 24-48 hours, but the ridge overhead of the system is rather thin, which should allow for Isaac to keep gaining significant latitude. By the 96 hour period, the ridge has broken down once again, and a more poleward motion might result before landfall. Overall, with the good agreement beween the ECMWF and the GFS, there is increasing confidence in this solution. Generally this track is supported by the vast majority of the model guidance.

200 hPa forecast comparison of the GFS and ECMWF. Plotted are 200 hPa heights (white contours) 200 hPa wind magnitude (color shading) and direction (vectors).

Taking a look at intensity, there is a little bit of disagreement. While the GFS has a large anticyclone over the system, which would tend to support robust development under low vertical wind shear, the ECMWF is a little bit less favorable, with an upper level low in the Gulf of Mexico initially imparting some southerly shear on Isaac. However, by 72 hours, this feature weakens and retrogrades, so the flow should become more favorable before the final landfall along the Florida panhandle. In addition to favorable shear, the system will be passing over very warm waters, with a good source of oceanic heat content. Much of the intensity forecast also depends on how well developed the inner core is after Isaac emerges off the Cuban coastline in the next 12-24 hours. Overall, the intensity guidance is forecasting intensification, but no models are very agressive, and none indicate rapid intensification. At this point, I am leaning towards the higher side of the guidance with the expectation that Isaac does not weaken too much over land in the short term.

First track forecast for Tropical Storm Isaac

With all of the following discussion, here is my first forecast for Tropical Storm Isaac. I think in the early going the track is likely to be right of most of the guidance owing to the current satellite trends and the fact that the storm is feeling the weakness at its strongest currently. At this weakness in the mid-level flow fills, the storm should bend back to a west-northwest heading from the 24-72 hour period. Finally, the track should once again bend back to the north as the ridge opens up again to the north of Isaac. Intensity wise, I think Isaac will intensify much more than expected owing to the further north forecast in the early going in comparison to the NHC. The storm remains well organized on infrared and I see no reason why it should collapse now that its passed the worst of the high topography. Thus, Im expecting a strong category 1 hurricane to impact the extreme southern Florida coastline in around 48 hours. The storm should continue to intensify as it gets in the Gulf of Mexico, and I have it peaking at the threshold of category 2/3 intensity in 96 hours. Landfall should occur shortly thereafter between Panama City and Pensacola on the panhandle of Florida. The system will be slowing down at this time, and there is a distinct chance it stalls after making landfall in the Florida Panhandle. Given that these details are still 3-4 days out, there could be some significant changes, although at this time I am reasonably confident in this solution.

Thats all I have time for today. Ill try to provide another update this weekend.

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Posted in Tropical Cyclone Forecast, Tropical Storm, Tropical Weather Outlook

Tagged 97L, Invest, Invest 97L, Isaac, Joyce, mid-level ridge, Tropical Storm Isaac, Tropical Storm Joyce, Trough, TS, TS Isaac, TS Joyce, upper level low, upper level ridge, weakness

Invest 94L Poised to Become a Tropical Cyclone, Invest 95L and 96L on Opposite Sides of the AtlanticBasin Posted on August 21, 2012 | Leave a comment

Tropical Activity for August 21st, 2012

And the tropics continue to remain active. Last week saw the development of Hurricane Gordon (now post-tropical) and Tropical Storm Helene (dissipated inland). To replace these three storms, we have three new threads to investigate, with particular attention being payed to the system in the middle (Invest 94L). Lets get right down to the nitty gritty details.

Invest 94L

Infrared animation of Invest 94L

Invest 94L has already been with us for a few days. As a rather potent wave emerging off of Africa, a lot of the guidance developed the system right away, and also took it significantly poleward over the first five days of its expected life. However, this forecast has not panned out, mainly due to the vast majority of models not accounting for the impact of the Saharan Air Layer (SAL) which has both kept the mid-level ridge stronger, forcing a faster westward track, as well as preventing rapid development of this disturbance. Over the past 6 hours, however, the system is starting to consolidate. Deep convection is finally developing close to the disturbance, and microwave imagery had previously shown the system had a well defined surface circulation. More recently, total precipitable water has increased over the system, despite a bit of dry air still trying to advect in from the western side. Shear continues to remain remarkably low over the system, with deep layer easterlies, which bodes well for future development. I agree with the NHC that this system has a near 100% chance of development over the next 48 hours, probably immediately later this morning.

GFS Forecast for Invest 94L. Animated above is the 925 hPa heights (black contours) 500 hPa heights (white contours) and 500 hPa vorticity (color shading).

With the development pretty much expected, where will this system track? At this point most of the guidance takes the system slightly north of due west over the northern Lesser Antilles and into the northern Caribbean Sea. While this seems to be a relatively confident solution, the models have currently handled the track of this disturbance poorly over the last few days. Once again, I think the track guidance might be a little too far north, especially if the system develops more than expected. Case in point, look at the 00z GFS (above). Note that the 500 hPa low center is significantly further south than the low-level center, which is displaced northward. This seems like an unlikely solution in the near term given that the system appears to becoming better vertically coupled. If the storm becomes vertically stacked (where the low and mid level low centers are aligned vertically) then the system will probably slide off further south, given the ENE/WSW orientation of the 500 hPa ridge. This should continue until the system makes it into the Eastern Caribbean. Beyond that period, the track of the system will be dictated on how much the 500 hPa ridge holds in place. The ECWMF keeps the ridge much stronger, which allows for 94L to move further west and stay in the Caribbean, while the GFS is further north, crossing both Hispaniola and Cuba. The track of Invest 94L will also strongly dictate intensity. Intensity guidance is split, with the global models (except for the ECMWF) showing little development, while the statistical models (LGEM, SHIPS) showing robust development over the next five days. Id be inclined to go with the statistical guidance given the recent trends of a further south track possibly occurring as well improved organization. As always, Ill keep you guys updated in the days to come if this become a major system.

Invest 95L

Infrared / Visible RGB combo animation of Invest 95L

Invest 95L has been hanging around for the last day near the Mexican coastline. At several points, its pulsed up with convection big time. However, recon flying earlier today was unable to find a well defined enough circulation to classify this system as a tropical cyclone. At this time, it looks like the system is still poorly organized, although convection is increasing. In addition, westerly shear has increased over the system which might limit further development. On the plus side, the system is still over very warm water and high oceanic heat content. In the end, the storm might just be running out of time to develop if it doesnt do so in the next 24 hours as the system is expect to slowly move east towards the Mexican Coastline. Intensity guidance suggets little development as well, so I am leaning against this system developing over the next 24-48 hours, and I am slightly under the NHCs 30% probability for development.

Invest 96L

Visible / IR animation combo of Invest 96L

Finally we have Invest 96L. This system emerged off the African coast in the last 48 hours, and already has a broad circulation. Deep convection has been confined to the SW quadrant of the system, but remains vigorous. This system is currently under favorable upper level winds, and decently warm SSTs, which might be able to promote development in the short term. In the long-term, however, upper level winds may become more unfavorable for development. Trackwise, the system is expect to travel west-northwest to northwest over the next few days as the mid-level ridge weakens somewhat over the Central Atlantic.

And that wraps up another tropical weather outlook. Look for more updates in the days to come about Invest 94L which seem poised to become Isaac.

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Posted in Tropical Weather Outlook

Tagged 94, 94L, 95, 95L, 96, 96L, ECMWF, GFS, Invest, Invest 94L, Invest 95L, Invest 96L, Isaac, Mid-level ridging, Saharan Air Layer, SAL, TS Issac, upper level winds

Ernesto in the Gulf of Mexico Reorganizing, Invest 92L Poised to Become the NextSystem Posted on August 9, 2012 | Leave a comment

Tropical Weather Outlook for August 9th, 2012

Hi again and welcome to another tropical weather outlook. Ernesto struck the Yucatan Peninsula yesterday just north of Belize as an intensifying category one hurricane. The storm has quickly moved across the Yucatan Peninsula and is now back over the Gulf of Mexico where it has already reintensified to near hurricane strength. In addition, we have another new system, Invest 92L, out over the open Atlantic that looks to be following in Ernestos footsteps. Ill have an overview of each system in this blog update.

Tropical Storm Ernesto

Enhanced Infrared Animation of Tropical Storm Ernesto

Ernesto has been on quite a journey, from nearly falling apart due to strong low-level easterlies in the Central Caribbean, to intensifying 20 knots in 6 hours as Ernesto came ashore as a formidable category one hurricane. While the minimum central pressure issued by the National Hurricane Center was officially 980 hPa, one storm chaser, Josh Morgerman, was able to get into the eyewall of Ernesto, recording a minimum pressure of 975 hPa on a Kestrel 4500. Since landfall, Ernesto has filled some, although recently convection has reorganized around the center as it has partially moved back over open water. A recent reconsisance mission was able to make three fixes on the storm, with maximum flight level winds of 86 knots, and a dropsonde measuring surface winds of 61 knots. Now that the system is over warm water, under low shear, and has extensive well established outflow, the storm should intensify for the next 6-12 hours and once again become a hurricane. However, Ernesto will likely make landfall tomorrow morning along the northern Mexican coastline somewhere between Veracruz and Coatzacoalcos. Radar is already showing Ernesto barreling in that direction. Overall, Ernesto has proven to be a very challenging storm to forecast, but the Global Forecast System (GFS) has preformed superior to most of the other global model guidance this go around.

Invest 92L

Nighttime Infrared RGB Animation of Invest 92L

With Ernesto about to make landfall for the last time, our attention turns to a developing disturbance out in the open Atlantic. Invest 92L formed from the African Easterly Wave that emerged in the wake of short lived Tropical Storm Florence (which developed from TD#6 in my last blog post). The system had been sliding along to the west, but has recently accelerated to the WSW in the overnight hours, mainly due to an enhanced NE/SW oriented mid-level ridge in the Central Atlantic. Recent microwave imagery has been hard to come by, but a TRMM pass that caught the edge of the system shows some convective towers near the estimated circulation center. Currently, the system is under favorable conditions, with low vertical wind shear (5-10 knots) , and warm sea surface temperatures (27-28 Degrees Celsius). However, the environment is not perfect, there is quite a bit of dry air surrounding the system, as evident looking at the total precipitable water, which is likely why the convective structure is pretty small at this time. This is further enhanced by a well established Saharan Air Layer (SAL). Thanks to the dry air surrounding the storm, only slow development is likely, and it may take another 24 hours for this system to become a tropical cyclone. However, given the favorable upper level conditions currently, Id say there is a pretty decent chance of that happening, and I agree with the NHCs 70% chance of tropical cyclone formation in 48 hours or less. Of course everyone wants to know, what might happen after that point.

GFS Forecast Image for 12z 11 August with Dynamic Tropopause (shaded) with 925-850 hPa mean layer vorticity (black contours) and winds on the Dynamic Tropopause (wind barbs).

At this point, there are two different synoptic scale features that are expected to battle for dominance over Invest 92L. The first of which is pictured above, a formidable tropical upper tropospheric trough (TUTT) that will extend downward in latitude over the next few days. This will cause the upper level flow to its south to slow as upper level westerly flow impinges on the tropics. How much this impacts Invest 92L will be dictated by how far south this feature extends, as well as the ultimate position of Invest 92L. At this point, though, it seems likely it will slow down the upper level flow somewhat, which would induce net westerly shear as the mid/low level flow is undisturbed.

GFS Analysis at 12z 8 August displaying kelvin wave filtered 200 hPa velocity potential anomalies (multi-colored contours, with cooler contours representing divergent flow), TRMM rainfall estimates (shaded) and 200 hPa anomalous winds (wind vectors).

However, thats not the only features influencing this disturbance. Like Ernesto, there also appears to be a progressing convectively coupled kelvin wave (CCKW) that might influence Invest 92Ls forecast. CCKWs in their active phase enhance convection through low-level convergence leading with upper level divergence following. A conceptual model of a kelvin wave reveals that the structure is tilted with the low-level convergence leading the upper level divergence. Since the diagram above shows the upper level portion of the Kelvin Wave, we can probably expect to see the low-level portion ahead of this feature. One benefit tropical cyclones and developing disturbances alike experience from CCKW (aside from enhanced convection) is that the vertical wind shear is reduced in the wake of these features as the upper level easterlies (on the backside of the divergence) is enhanced, while the low-level easterlies are reduced. Thus, this might help to negate some of the negative westerly shear that the TUTT might impart on this feature. One other important piece of information needed when forecasting with these features is that CCKW are typically centered along the equator, which means their influence decreases the further poleward a feature is located. Thus, if Invest 92L wants to have a better upper level environment for the future, it would be beneficial for it to move further southward, both staying further south of the TUTT, and also being better influenced by the CCKW. We will see where the current WSW motion of Invest 92L will lead it down the road. At this point, the track and intensity are both looking very Ernesto like at this point, and I see no reason to forecast anything different, with TCG genesis likely in the next 24-48 hours, with a weak to moderate tropical storm impacting the Lesser Antilles.

And thats it for another tropical weather outlook. There is another African Easterly Wave (AEW) emerging off the coastline over the next 24 hours, but its worth waiting to see if it will be significantly impacted by the SAL outbreak occurring ahead of it. Ill try to previde an update in the days to come on Invest 92L and potentially this new feature off the African coast.

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Posted in Tropical Storm, Tropical Weather Outlook

Tagged 92, 92L, CCKW, Ernesto, H, Hurricane, Hurricane Ernesto, Invest, Invest 92, Invest 92L, Tropical Storm, Tropical Storm Ernesto, TS, TS Ernesto, TUTT, upper level winds, vertical wind shear

Ernesto Getting Better Organized, TD #6 Develops, Invest 91L Along the FloridaCoastline Posted on August 4, 2012 | Leave a comment

Tropical Weather Outlook for August 4th, 2012

Hi again and thanks for stopping by to read another tropical weather outlook. August is wasting no time becoming very active, with three areas worth watching, two of those now designated as tropical cyclones. Ernesto is still the main story, as it continues to turn across the Caribbean and appears to be getting better organized. TD #6 is new to the world, but is way out in the East Atlantic, just off the African Coastline. Finally, we have an invest much closer to the United States. Ill talk about each feature in Todays outlook!

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Tropical Storm Ernesto

Visible/Infrared Imagery Animation of Tropical Storm Ernesto

After a difficult day fighting westerly vertical wind shear and dry air intrusions, Ernesto has re-organized somewhat overnight. Ernesto looked like skeleton last night with limited deep convection and only minor rain bands surround the circulation on radar. However this past evening, deep convection is much more organized surrounding the center in all quadrants alongside improved banding features which are indicating a better organized system. A deep burst of convection earlier has resulted in an expansion of outflow to the western side of the circulation, the first time this has happened by any significant margin. Water vapor shows this nicely, with upper level easterlies pushing the outflow ahead of the system. Vertical wind shear as a result has decreased to 5-10 knots as an upper level anticyclone builds over the system. This low vertical wind shear, alongside both warm sea surface temperatures (SSTs) and very high oceanic heat content (OHC) spells a recipe for further intensification. One slight limiting factor might be lower precipitable water in the storms path. However, in a low shear regime this lower atmospheric water vapor wont be as much of a limiting factor. In fact, its primary impact might be to limit the size of Ernesto as it moves westward across the Caribbean. So now that Ive gotten the past and present out of the way, where is Ernesto going, and will this pose a threat to land as a significant Tropical Cyclone down the road?

ECMWF in 3 hour intervals. Plotted are 925 hPa heights (black contours), 500 hPa vorticity (shaded), and 500 hPa heights (white contours).

To illustrate this threat, lets first talk about track of Ernesto. Normally I would show a 500 hPa plot of both the ECMWF and contrast it with the GFS. However, both global models are having a hard time accurately depicting the circulation, especially after the recent organization that has taken place overnight. Instead I want to illustrate why I think the ECMWF (and to a lesser extent the GFS) might not have the correct solution. Pictured above is the 925 hPa heights from the ECMWF from 00z Last Night to 12z on August 5th. Overlaid is the 500 hPa vorticity and heights. Notice how the low-level circulation quickly runs out away from the mid-level circulation. This typically occurs when there is significant vertical wind shear. I am having a hard time believing that the low-level flow is going to rapidly increase to the point that it causes the low-level and mid-level centers of Ernesto to decouple. This problem with this forecast is that the vertical wind shear over Ernesto is decreasing currently. As long as the low and mid-level centers do not separate, we should see a more vertically coherent system which should be able to feel the weakness in the Mid-latitude trough that will develop over the Gulf of Mexico in the longer range.

ECMWF 120 Hour Forecast at 500 hPa. Note the weakness in the Gulf of Mexico.

The track guidance splits in the long range mainly due to differences in intensity. I ultimately believe the most rightward tracks will prevail, especially if Ernesto intensifies more than expected. Intensity wise, things will probably still be slow going for the next 24-48 hours as the storm develops an inner core and negates some of the dry mid-level air nearby. However, once the storm is in the Western Caribbean all things are a go for robust development, and rapid intensification wont be out of the question. The intensity guidance is very bullish, especially the statistical models. At this point, Ill stay on the low side for the firt 24-48 hours, but beyond Ernesto could rapidly intensify and that will be reflected in the forecast.

Forecast #1 for Tropical Storm Ernesto

Here is my first forecast for Ernesto. You can see that in the short term I have Ernesto only slowly intensifying until it reaches the Western Caribbean. From here rapid intensification takes place between 72-96 hours, although the time period where this takes place will be exceptionally difficult to forecast. From there it is likely that Ernesto will clip the Yucatan Peninsula which will limit its maximum intensity. Still though, I think this is a very bullish forecast in the long term. Stay tuned for updates in the days to come!

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Tropical Depression #6

Visible/Infrared Animation of Tropical Depression #6

Tropical Depression #6 formed last night way out in the East Atlantic close to the Cape Verde islands. While the system was originally being sheared from the northeast, a recent microwave pass shows substancial organization since then, with even hints of an eyewall trying to develop. Needless to stay this system is likely intensifying as we speak and we will likely be looking at Tropical Storm Florence later today. The future for this system outside of the short term though, looks rather bleak, with cooling SSTs and a dry stable Saharan Air Layer that might put a damper on convection beyond 48 hours. Consequently, both the GFS and ECMWF dissipate the system beyond 72 hours. Ill keep you updated on this system as well in the days to come.

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Invest 91L

Enhanced Infrared Image of Invest 91L

Finally on our list we have Invest 91L. This system developed yesterday afternoon from an old tropical wave that is now interacting with an upper level low. More recently, the upper level low has been moving away which has lead to slightly more favorable conditions. However, the system will have to get more organized soon before it moves inland over Florida. Thus far, radar animations show that the convection with the system is still meager, and it will take a substancial uptick in convection for this system to organize further. At this time Im giving 91L a 30% chance of development, which is slightly higher than the National Hurricane Center (NHC) currently.

And thats all I have (phew) for todays tropical weather outlook. Look for another update tomorrow!

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Posted in Tropical Depression, Tropical Storm, Tropical Weather Outlook

Tagged #6, 91, 91L, Decoupling, ECMWF, Ernesto, GFS, Invest 91, Invest 91L, rapid intensification, TD, TD#6, Tropical Depression, Tropical Depression #6, Tropical Storm Ernesto, TS, TS Ernesto, Vertical Coherience

Tropical Storm Ernesto Forms IntensityUncertain Posted on August 3, 2012 | Leave a comment

Tropical Weather Outlook for August 3rd, 2012

Hi everyone and welcome to another tropical weather outlook. The tropics after remaining completely inactive in July have heated up quite substantially in the first week of August. Within the past day Tropical Storm Ernesto has formed just east of the Lesser Antilles and could potentially be a player out into the Caribbean and Gulf of Mexico in the days to come. In addition there is also a nice looking tropical wave that recently emerged off the African Coastline. Ill have all this and more in todays tropical update.

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Tropical Storm Ernesto

Enhanced Infrared Imagery of Tropical Storm Ernesto

August is certainly starting off fast, with our fifth named tropical cyclone occurring on the second day of the month. Ernesto developed from a low amplitude tropical wave that emerged off the African coast around a week ago. During the early part of this week, the wave started to show evidence of organization, and the GFS was very adamant with development before reaching the Lesser Antilles. The ECMWF was conversely bearish with a weaker cyclone signature in the low-levels. Thus, the GFS has preformed better both in regards to track and intensity with the system in its early life. Despite this, the system is still battling some moderate shear (15-20 knots). While the system has managed to slip under the large upper level low located further to the northeast, the flow has still been slowed by this feature in the upper levels over Ernesto. The easterly low-level flow is not impeded by the upper level disturbance, so it is in effect outrunning the slower upper level easterly flow, creating the net westerly shear. While upper level easterlies prevail across the vast majority of the Caribbean Sea, they are still slower than the low-level flow which is amplified through the narrower Caribbean Sea surrounded by the higher topography of Central America and the Greater Antilles. The Eastern Caribbean is also know as the Tropical Cyclone Graveyard due to the large number of systems that have succumbed to unfavorable conditions in this part of the Atlantic basin. While the convective organization (above) leaves much to be desired, microwave imagery has shown evidence of modest banding features around the center with a decent surface circulation. So where do we go from here, can Ernesto be a big storm on the horizon, or is it merely a speed bump in this years season?

Intensity Guidance for Tropical Storm Ernesto

Lets first start off with intensity, since it will likely dictate the track of Ernesto. Seen above is a suite of intensity model guidance for Ernesto over the next 5.5 days. Notice that there is a large spread in intensity from remaining a weak tropical storm to intensification into a cat 2 hurricane. It is interesting that there seems to be a bit of a split between the statistical guidance (LGEM, SHIPS, SHF5) forecasting robust intensification versus the dynamical models (the ones based on real physical equations) forecasting only modest intensification (GFS, HWRF, GFDL). The official forecast from the NHC essentially splits the difference. Given the aforementioned environment and the fact that this tends to be an unfavorable region in the Atlantic Basin, I would argue against the significant strengthening expected from the statistical models over the next 48-72 hours as the storm traverses this less than favorable environment. However, in the longer range, the system is expected to slow down substantially in the Western Caribbean. If Ernesto survives to this point, it could find itself in a much more favorable environment which results in more significant intensification. If that solution occurs, this storm could post a more substancial threat to Mexico and possibly the United States. Stay tuned!

Track Guidance for Tropical Storm Ernesto

The track of Ernesto is a little bit more straightforward. As the mid-level level located to the north remains firmly in place, Ernesto should continue westward with a slight northward component. Where the track guidance diverges the most, though, is towards the end of the forecast. Some of this uncertainty is due to the expected intensity of Ernesto. The weaker guidance has generally been further south (like the ECMWF). Some of the more intense guidance shows a northward bend towards the end of the forecast track (like the HWRF). At this point, I think Ernesto will stay along the middle, although perhaps on the south side as it remains a weak system. If it starts to intensity in the Western Caribbean like some of the guidance suggests, then we may see a northward turn beyond 120 hours. There is still a lot of things up in the air, and plenty of time to watch and see how things pan out. Ill give a more detail updated in the days to come if warranted.

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Tropical Wave Off Africa

Infrared Image of an African Easterly Wave

In addition to Ernesto, we also have a new wave that has emerged off the African coastline. This one looks fairly potent, with a deep convective shield. In addition, microwave imagery shows some evidence of a circulation. Currently the system is situated under favorable easterly upper level flow, with ample high precipitable water. In addition, it has model support from both the GFS and the ECMWF in the short term. Thus, I think it has a semi decent chance at becoming a tropical cyclone, and Ive placed my probability at 40%, much higher than the NHCs 10% currently.

And with that, we round off another tropical weather outlook. Look for more updates from Ernesto in the days to come, if it survives!

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Posted in Tropical Storm, Tropical Weather Outlook

Tagged 99, 99L, African Easterly Wave, ECMWF, Ernesto, GFS, Invest, Invest 99, Invest 99L, Strong low-level easterlies, Tropical Storm, Tropical Storm Ernesto, TS Ernesto, Uncertain Forecast

Tropical Storm Debby is Born, A Tricky Track ForecastRemains Posted on June 23, 2012 | Leave a comment

Tropical Activity For June 23rd, 2012

And just like that we are off to the fastest start for an Atlantic Hurricane Season ever. Tropical Storm Debby formed this afternoon from Invest 96L which as continued to drift northward and is now located in the East Gulf of Mexico. Debby is the only major player in town, so todays discussion will focus on the tropical storm. Read all about it below.

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Tropical Storm Debby

Visible Animation of Tropical Storm Debby

Tropical Storm Debby still has a very broad circulation that is displaced west of the deepest convection. The visible animation above shows the circulation is comprised of a series of mesovorticies that are rotating around a mean center. This has also been evidence from the recon observations, which have already picked up on two particular centers, one located further to the northeast closer to the deeper convection. With a broad and diffuse center in place currently just outside of the convection, there is some possibility of center relocation if one of the mesovorticies becomes dominant under the deeper convection helping to pull the mean center further east. At this point, the maximum sustained winds are 50 mph and slow strengthening is expected as the storm moves slowly northward over the open waters of the Gulf of Mexico. At this point, Debby is embedded in an environment of high precipitable water, and high Sea Surface Temperatures at 28-29 degrees Celsius. The Oceanic Heat Content is also relatively high. However, the main limiting factor holding Debby back is vertical wind shear, which is out of the south from 20-30 knots. The vertical wind shear is caused by a southwestward moving upper level low, which is located in the western Gulf of Mexico. The shear is likely to continue as long as the upper level low is present.  So where will Debby move to in the coming days, and what areas are under the threat from this tropical cyclone. Ill have an update later tonight with a track and intensity outlook.

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Posted in Tropical Storm

Tagged 96, 96L, Anticyclone, Debby, Invest 96L, Mesovorticies, oceanic heat content, recon observations, sea surface temperatures, Tropical Storm Debby, TS Debby, upper level low, vertical wind shear

Invest 96L Getting Better Organized, Track RemainsUncertain Posted on June 23, 2012 | 2 comments

Tropical Activity for June 23rd, 2012

The tropics continue to remain unusually active over the past few days, first with Chris turning up the maritime waters in the far North Atlantic, and now Invest 96L which looks to do some water turning of its own as it spins across the Gulf of Mexico. Now that Chris has become a post-tropical disturbance, our attention shifts to 96L which is poised to be the big tropical topic of discussion into the next work week. Ive got the latest details below.

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Invest 96L

Infrared Imagery of Invest 96L

Invest 96L has been taking its sweet time getting organized, the biproduct of a large gyre-like disturbance that organized through a northward progression of the intertropical convergence zone (ITCZ) merging with a disturbance off the Panama coast. Now the feature has been slowly moving northward in the Gulf of Mexico. Dont let the convection fool you, the center is actually further west in region mainly devoid of convection currently. However, there are individual meosvorticies that are rotating around a larger mean center that are interacting with the convection. The lopsidedness nature of the system is partially due to 20-30 knots of westerly vertical wind shear over the circulation, which is being caused by a upper level trough dropping down from Texas into the Western Gulf of Mexico. This has caused the upper-level anticyclone to be displaced further east of the storm. All of these factors will probably prevent rapid development in the short term, although the system is still gradually getting better organized, and we will likely see tropical cyclogenesis (TCG) sometime in the next 24-48 hours. I am in agreement with the NHCs assessment that this system has an 80% chance of development in the next 48 hours. With that said, what does the future hold; how strong can 96L get, and where is it going to go?

500 hPa model evolution of both the ECMWF and GFS runs from 00z on 23 June. Plotted are the 500 hPa absolute vorticity (shaded) as well as the geopotential heights (contours). Relevant features are highlighted

Trackwise, things are very much split at this time. This is highlighted in the most recent plot of the model track guidance, showing two main groups taking the system is opposite directions. This difference is highlighted by looking at both the 00z runs of the ECMWF and GFS. The first observation worth noting is that there are not huge differences in the mid-level pattern between each run in the 24-48 hour time frame. The ECMWF does have a touch more ridging in place at 48 hours, but this difference is minor. What is significant though is the estimate position of 96L in both time frames. The ECMWF is distinctly further south and ever so slightly further west. This allows the system to be captured by the easterly flow on the back of an amplifying ridge, which then steers the system westward towards the Texas coastline. The GFS is the polar opposite. The system goes too far north, so the ridge is not able to capture the disturbance fully. Instead, the mid-latitude flow associated with an amplifying trough in the Eastern United States captures the system and the westerly flow associated with the East US trough draws the storm eastward across Florida and then out into the open Atlantic. While these differences are extreme, 96L starts off in very similar positions for the first 24-48 hours, which highlights how key the initial location of this system is. With gyre like circulations such as this, individual mesovortices often can pull a mean center towards that piece of vorticity if the feature is strong enough. Since the convection will likely be focused on the eastern flank of the circulation, there is a decent chance one of those mesovortices could pull the system further east than expected in the short term. This would tend to lend credence to the GFS solution. If the system moves too far northward, it could very well be captured by the amplifying trough that will dig into the east by 72 hours. At this point, its difficult to make a call either way due to the formative nature of this disturbance, but it is likely we will have better agreement by this time tomorrow when the circulation becomes better defined. Thus, for those that have interests in the Gulf of Mexico, stand on guard anywhere from the TX/MX border all the way to the Florida Peninsula. This system simply has not yet decided where it wants to go.

ECWMF Forecast plotting 200 hPa winds (shaded) and heights (contours)

Intensity is also still somewhat up in the air. Most of the intensity guidance is painting very slow intensification, with the statistical guidance being the most bullish calling for a moderate tropical storm. The main reason for the slow intensification trend is the continuation of moderate vertical wind shear, thanks in part to an upper level low that will be rotating to the west of 96L. This will probably limit development for the first 24-48 hours, although this feature is forecast to weaken later in the period. At this point I dont want to get too caught up into the details, as much of this intensity forecast will be directly linked to the ultimate track this disturbance takes. In the end, the biggest threat remains very heavy rainfall which has already been experienced across the Florida coastline and will likely continue over the next few days.

Thats all I have for the time being as the rest of the tropics are now quiet. Ill try to give another update on 96L, possibly Debby by tomorrow.

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Posted in Tropical Weather Outlook

Tagged 96, 96L, Debby, ECWMF, flooding, Flooding Rainfall, gyre, Invest 96L, Mesovorticy, TD, TD #3, Tropical Storm Debby, TS Debby

Chris Becomes a Hurricane, Large Disturbance in the Gulf of Mexico (Now Invest96L) Posted on June 21, 2012 | Leave a comment

Tropical Activity for June 21st, 2012

I took an extended break over the past couple of weeks, and now that Im back the tropics are starting to heat back up despite being relatively early in the season. Tropical Storm Chris which formed yesterday has just been upgraded to the first hurricane of the 2012 hurricane season as it meanders well into the open waters of the north Atlantic. Meanwhile, there is a new disturbance organizing in the Gulf of Mexico which could be a more substancial player in the days to come. Read all about it in this tropical weather update.

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Hurricane Chris

Enhanced Infrared Imagery of Hurricane Chris

The hurricane season thus far has proven to be an early bloomer. After recording our first two tropical cyclones of the season in May, the season has continued its early season by providing us with the third named system in June and our first named hurricane, which is much earlier than normal. For a comparison, Irene was the first named hurricane in the 2011 hurricane season, which occurred in late August! In any event, the origin of Chris can actually be traced back to a non-tropical low pressure that developed along a decaying frontal boundary. As the front continued to decay, an upper level potential vorticity (PV) maximum moved over the non-tropical low pressure, and quickly allowed the low pressure to occlude and undergo warm seclusion as it detached from the frontal boundary and became vertically stacked with the upper level disturbance. Deeper convection then began to form around the circulation as the temperature gradient between the marginal sea surface temperatures (SSTs) compared to the anomalously cold upper level temperatures was sufficient for deeper convection. At this point, the system had a decent warm core, and the National Hurricane Center (NHC) felt that the deep convection and overall more tropical nature of the storm was sufficient for an upgrade. Beyond this time, the system has only become better organized, with an eye feature developing on IR as early as last evening. The visible imagery this morning is particularly impressive with spiral bands and moderate deep convection surrounding the eye in all quadrants. Despite the current well organized appearance, the system is quickly moving towards colder waters even less supportive of a tropical cyclone, so its unlikely Chris will be able to continue to intensify as an tropical system. However, there is a 60-70 m/s jet streak located to the west of Chris which is aiding in divergent upper level flow on the left exit region of the jet streak. This will probably allow Chris to transform into a powerful extra-tropical cyclone as it moves over the cooler waters of the north Atlantic.

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Gulf of Mexico Disturbance (Now Invest 96L)

Visible Imagery of the Gulf of Mexico Disturbance

With Chris moving out of the picture, the next threat turns to something closer to home that is beginning to organize in the Gulf of Mexico. A very large circulation is developing in the Gulf of Mexico. Currently, we have a broad area of 850 hPa vorticity that is elongated from the Yucatan Peninsula up into the east Gulf of Mexico. This area of vorticity is associated with deep convection, although it is displaced somewhat to the south and east of the vorticity, which is obvious looking at the visible loop above. The convection is also associated with a developing upper level anticyclone, which is helping to ventilate the convection in the upper levels. The biggest questions in the coming days is what will this large broad circulation do, and who will be affected.

ECMWF Forecast for the large-scale circulation that develops over the Gulf of Mexico. Plotted are 500 hPa absolute vorticity (shaded) and geopotential heights (white contours). Annotated features are highlighted.

Animated above is the 00z ECMWF showing absolute vorticity and geopotential heights. I have highlighted the relevant features that will influence the development and track of this feature for the next 5 days. First, I want to draw your attention to the orange shaded areas of cyclonic vorticity. These represent the multiple mesovorticies that are rotating around the larger circulation that is centered over the Gulf of Mexico. While initially these areas of vorticity are small and diffuse, they start to merge over the Eastern Gulf of Mexico east of the mean low level circulation center by day 3. This type of circulation evolution is similar to how tropical cyclones develop in large gyre-like circulations that traditionally occur in the West Pacific Basin. For more reading on these types of cyclones, there are several good papers by Lander (1994) and Molinari and Vollaro (2012) that document the development and evolution of these types of systems. While the gyre circulation is relatively large, it moves very slowly for the first 3-4 days, as the upper level ridge attempts to develop eastward across the deep south in the wake of a weak trough. However, by the end of the forecast period, the upper level ridge gives way, and the westerly flow associated with a series of weak upper level troughs starts to pick up the developing tropical cyclones in the Eastern Gulf of Mexico. A word of caution. While this is one solution depicted from the ECMWF, the forecast genesis of a tropical cyclone (TCG) is still a big unknown. It all depends on which area of vorticity becomes the dominant feature and where these individual mesovorticies decide to merge. The spatial scale of most of the global models is simply too coarse to predict which convective elements will influence the development of this feature. The GFS provides a different solution, with vorticity becoming focused east of the Florida coastline rather than in the Gulf of Mexico. With the potential TCG of this event still a good 2-4 days away, there will probably be large jumps in the modeling, as the models get a better handle of the convective elements rotating around the larger circulation. At this point, there is no done deal that this system will evolve into a tropical cyclone, and Im in support of the NHCs outlook of a 30% chance of tropical cyclone development in the next 48 hours. I do think the chances for TCG do increase beyond that time frame, however. Given the broad nature of this disturbance, development will be very slow

GFS forecast at 54 hours with Standardized Anomalies of Precipitable Water (shaded) and 700 hPa winds (wind barbs)

One thing that is probably a safe bet though is torrential rainfall from the Yucatan coastline of Mexico across into Cuba and most of Florida. This circulation will be tapping into a precipitable water environment that is 3-5 standard deviations above average. This moisture originates from moisture originally drawn up from the intertropical convergence zone (ITCZ) that moved northward across Central America after the landfall of Hurricane Carlotta. Thus, while TCG may still be up for debate at this point, the threat for life-threatening flooding rainfall across the large area is a very real concern on the south and eastern regions of this large scale circulation. Even this morning, a sounding from Key West, FL (KKEY) showed total precipitable water at 2.43 which is near its record value. This is very impressive considering how moist south Florida typically is this time of the year. This very deep and moist atmosphere will only continue to spread northward with time as the low level flow associated with the circulation continues to spread an influx of moisture from Central America northward.

Aside from these two features, there isnt much else happing, and the East Pacific is quiet after Carlotta hit last week. Ill keep you updated on the latest in the Gulf of Mexico, and until then enjoy the rest of your work week!

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Posted in Hurricane, Tropical Weather Outlook

Tagged 96, 96L, Chris, Divergence, ECMWF, GFS, Gulf of Mexico Disturbance, Hurricane, Hurricane Chris, Infrared, Invest, Invest 96L, Jet Streak, Potential Vorticity, Precipitable Water, TCG, tropical cyclogenesis, upper level ridge, Visible

Beryl Transitioning into a Tropical Cyclone, Will Make Landfall in the Southeast United StatesTonight Posted on May 27, 2012 | Leave a comment

Tropical Activity for May 27th, 2012

Beryl continues to chug along to the west-southwest, as it slowly organizes into a legitimate tropical storm as the convection increases. While there isnt much else going on in the tropics (Bud dissipated yesterday along the Mexican coastline) its still May for crying out loud! Lets get down to the details.

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Subtropical Storm Beryl

Infrared / Visible Satellite Imagery combo of Subtropical Storm Beryl

Beryl has slowly become better organized over the past 24 hours. Deep convection is developing over and around the system for the first time, and is attempting to wrap around the circulation. This recent increase in convection is likely due to the storm traversing over the warmer waters of the Gulf Stream during the overnight diurnal maximum in convection. The convection will also start to build upper level outflow over the system, which will overcome the current upper level cyclonic flow that is still sitting over the system. As this takes place, Beryl will transition into a true tropical cyclone. In the meantime, reconnaissance aircraft actually found the system had intensified, with flight level winds of 65 knots to the northeast of the system. This translates to roughly 50 knots at the surface. Shear continues to remain low over the system (10-15 knots) meaning developing convection should have no problem wrapping around the center.

Radar Reflectivity Animation of Subtropical Storm Beryl

Radar reflectivity shows the improved organization over the last 4 hours. Convection is continuing to build and wrap into the center as the storm transitions over to a tropical cyclone. One thing that might curtail further development, however, is the cooler shelf water that lies closer to the Florida coastline. So whats my take on this system, and will this ruin those beach plans for the Memorial day festivities?

High Resolution Rapid Refresh Model (HRRR) depicting radar reflectivity. Areas that are most likely to be impacted significantly from Beryl are shaded.

For the short term forecast, Im going to use the high resolution rapid refresh model, mainly due to its superior resolution which is able to resolve individual cumulus convective cells (meaning no cumulus parameterization is necessary). This allows for a more realistic simulation given accurate data assimilation. What is evident is that the storm is likely to continue to move westward as a steady clip. I believe this model is too fast in the short term, and landfall is more likely to occur in the overnight hours (near midnight) rather than right at sundown (00 UTC / 8 PM EDT). However, I think the location pegged for landfall is likely to verify as well as the overall precipitation shield associated with the system. Thus, folks from Savannah, GA all the way down to Daytona Beach, FL will probably be under the gun for heavy rains, potentially resulting in flooding. This will be the main threat associated with the storm, with wind still being a significant, but lesser threat. The combination of heavy rains, and gusty winds through still may be enough to uproot trees which can bring down powerlines along with them. Thus the area in the red-dotted line should take great caution in any Memorial Day related activities tonight and tomorrow as the storm moves ashore. At this time, I still dont think Beryl will have enough room or warm water to be able to intensify into a hurricane, although another 5-10 knot increase in intensity in the next 12 hours is certainly not out of the realm of possibility. I remain confident the system will also transition into a tropical cyclone before landfall.

00z ECMWF Forecast Evolution of Subtropical Storm Beryl at 500 hPa with vorticity (shaded) and heights (white contours, every 60 m)

Beyond the next 12-24 hours, Ill use the ECMWF to illustrate where I think Beryl will go next. While the storm is onshore it will likely weaken back down to a tropical depression. However, heavy rain will likely continue across northern Florida and northward into Georgia as the storm drifts aimlessly for the next 24 hours. The subtropical high that was dominating its motion over the past few days will be force southward as a mid-latitude trough swings across the United States. This system should be strong enough to pick up Beryl, drawing it northeastward. The track guidance remains somewhat split on whether the system will remain inland or emerge back over the open waters of the Atlantic Ocean, but the vast majority take it along the coastline. There is some suggestion the storm might be able to re-intensify it it emerges back over water, with most of the intensity guidance bringing it back to tropical storm strength in the latter half of the forecast period. This is supported by the ECMWF. However, some of this intensification will likely be taking place due to baroclinic processes (jet streak induced divergence) , a precursor to extra-tropical transition. Overall, I agree that Beryl will re-intensify but perhaps more as an extra-tropical cyclone as it speeds up off the coast of Cape Hatteras, NC. To everyone in the southeast, make sure you plan accordingly for Beryl during this Holiday.

EDIT: as of the 2pm EDT intermediate advisory, Beryl has transitioned into a Tropical Storm as expected.

EDIT 2: Tropical Storm Beryl has made landfall at Jacksonville Beach, FL as of 12:10 am EDT with maximum sustained winds at 70 mph.

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And thats it for this tropical weather update. Ill be out of town for the next week, so its unlikely Ill be able to update unless I have enough time, but until then, thanks for reading!

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Posted in Tropical Storm, Tropical Weather Outlook

Tagged 60-70mph landfall, Baroclinic processes, Beryl, Daytona Beach, deep convection, Divergence, extratropical, FL, Flooding Rainfall, Florida, GA, Georgia, North Carolina, radar, Savannah, South Carolina, subtropical storm, Subtropical Storm Beryl, Tropical Storm, Tropical Storm Beryl, Tropical Transition, upper level low

Subtropical Storm Beryl is Born, Bud Quickly Falling Apart Along the MexicanCoastline Posted on May 26, 2012 | 1 comment

Tropical Activity for May 26th, 2012

And then there was two! Subtropical Storm Beryl becomes the second named storm of the Atlantic Hurricane season, which has certainly been impatient, with the second named storm starting 5 days before the official start on June 1st. Meanwhile, Hurricane Bud has weakened to a tropical storm and is quickly falling apart even before making landfall in Mexico. Ill have all the particulars and more below in this tropical weather outlook!

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Subtropical Storm Beryl

Enhanced Infrared Satellite Imagery of Subtropical Storm Beryl

Subtropical Storm Beryl formed today from the combination of Invest 94L with an amplifying upper tropospheric trough that developed overhead of the system. In my post I made on the 24th of May, I alluded to how this interaction is likely a favorable precursor to a tropical transition event. Indeed we are already seeing the process underway, as the deep convective shield association with the system shifting from the eastern side to the western side of the system, as the upper level disturbances moves overhead. One look at the satellite derived upper level winds reveals this upper level cutoff disturbance. The reason for the subtropical classification is simple. Typical tropical cyclones are associated with an upper level anticyclone, or winds rotating clockwise in the upper levels of the atmosphere. In the case of many subtropical cyclones, these winds continue to be cyclonic, or rotating counter-clockwise in the upper portions of the atmosphere. However, subtropical cyclones possess the capability of transitioning over to a tropical cyclone, where deep convection produces diabatic heating that weakens the upper level cyclone and helps to develop upper level anticyclone flow aloft. Right now this deep convective activity is lacking somewhat near the center of circulation. However, as the storm continues to move slowly west-southwestward across the Gulf Stream, sea surface temperatures (SSTs) will be around 26-27 degrees Celsius which is marginally supportive of a tropical cyclone. Of even greater importance is the fact that these warm SSTs will also be occurring in an upper level thermal environment that is colder than normal, providing a supportive thermal gradient to allow deep convective development. One thing the storm already has going for it in its quest for full tropical characteristics is a significant warm core in the mid-levels of the atmosphere. Look for this warm temperature anomaly aloft to continue to increase if the storm obtains full tropical characteristics. Vertical wind shear is still rather high (~30 knots) although this is substantially less than the 70 knots that were ripping through the system yesterday. This value has been trending downward as the relative calm of the upper level cyclone moves overhead. One other negative factor for this systems future intensity is the large amount of dry air that surrounds the storm. So with all these factors being observed, what is going to happen to Beryl over the next few days, and does it pose a threat to the United States?

12z ECMWF Forecast Evolution of Subtropical Storm Beryl at 500 hPa with vorticity (shaded) and heights (white contours, every 60 m)

Lets first try to answer the track question. This is actually relatively straightforward when looking at the mid-level flow (above). Note that Beryl will initially be steered by a powerful mid-level high which will become anchored over the Eastern United States for the next 48 hours. This will lead Beryl on a west-southwest track for the next 48 hours as the high will build over the system, preventing any northward progression. At this point, it looks like the ridge is going to be strong enough to force Beryl inland over the northern Florida coastline at some point Sunday night. However, beyond this period, the ridge starts to breakdown as an upper level trough form the Western United States manages to erode the ridge back southward into Texas. This upper level trough will then provide mid-level westerly flow which will then pick up the system towards the end of the forecast period and steer it back to the east-northeast, potentially back offshore. The track evolution on the ECMWF is close to what the vast majority of the track guidance is showing for Subtropical Storm Beryl, although a large portion of the guidance remains further north and onshore in the later time periods.

Intensity might prove to be the more difficult variable to forecast for this particular storm. Intensity guidance for this system is pretty stagnant, with no model making the storm stronger than 45 knots. However, models tend to do a poor job in unusual regiemes such as this one. Upper level winds are expected to be relatively weak over the system as the upper level cyclone slowly decays. Ultimately, intensification of Beryl will rely on how effective it is able to tap the marginally warm waters of the Gulf Stream over the next 48 hours. With that said, I think its relatively unlikely that Beryl will be able to become a hurricane. However, I do think the chances are pretty good that Beryl will be able to transition into a full tropical cyclone as it should have a long enough period to generate enough deep convection to allow this process to occur. At this point, the biggest threat the Beryl poses to the United States is heavy rainfall and flooding, especially after the system stalls over the Southeastern United States. Folks in Florida, Georgia, and South Carolina especially near the coastline need to plan accordingly, and unfortunately a lot of Memorial Day plans may have to take place indoors. Ill have an update on this system tomorrow unless major changes take place.

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Tropical Storm Bud

Enhanced Infrared Imagery of Tropical Storm Bud

Tropical Storm Bud has pulled a fast one right before our eyes. While yesterday the storm was looking rather formidable as a category 3 hurricane and moving steadily towards the northeast toward Mexico, the storm has all but vanished in the subsequent 24 hours. Convection has largely dissipated over the circulation center due to a combination of increasing vertical wind shear, and a large reservoir of dry air in close proximity to the circulation center. Dry air played a greater than normal role in the demise of this storm thanks in large part to a subsident phase of a Kelvin Wave that was traversing through. This leads to large scale decent which can be overcome when vertical wind shear is low, but is hard to avoid when vertical wind shear is advecting dry air into the circulation center. In this case, the light to moderate westerly shear was just enough to allow the convective processes fueling Bud to be shut off, resulting in a complete collapse of the storm structure and associated convection. Bud will continue to spin down as it stalls and slowly moves back to the southwest with the low-level flow.

And thats it for another tropical weather outlook. Ill try to update things again tomorrow on Beryl, so until then, thanks for your time!
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Posted in Tropical Storm, Tropical Weather Outlook

Tagged Beryl, Bud, Dry Air, Gulf Stream, Hurricane, Hurricane Bud, sea surface temperatures, Subtropical, subtropical storm, Subtropical Storm Beryl, Tropical Storm, Tropical Storm Beryl, Tropical Storm Bud, upper level low, vertical wind shear, warm core

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