CybrTeddy's tropical weather blog

92L disorganized, Tropical Storm Erin forms, another Cape Verde storm soon? 8/15/13

By: CybrTeddy, 1:14 PM GMT on August 15, 2013

Good morning everyone and welcome to my tropical weather update for Thursday, August 15th, 2013. I haven't been able to pull together a tropical weather update as I've lost all my stuff as the result of a lightning strike. I've only recently been able to pull all my links together to make another update.

The Atlantic has finally ignited with the long expected burst of activity. We have two areas of interest to watch out for, the former is Invest 92L currently situated virtually over the Yucatan Peninsula, and the second is newly designated Tropical Storm Erin just south of the Cape Verde islands. Both of these areas of disturbed weather hold little threat to the United States right now, but there may be more storms on the horizon that pose a greater threat to track.

Invest 92L unlikely to become a major system.
The first area of interest we have to discuss is Invest 92L currently situated in the extreme western Caribbean. Yesterday it appeared likely that Invest 92L would organize into a tropical storm today and would be a threat to become a strong tropical storm in the Gulf of Mexico.  This is no longer the case today, as 92L's convection has completely collapsed as it moves inland towards the Yucatan.

Invest 92L lost all of its surface convergence and divergence overnight during the diurnal minimum period last evening. Thunderstorms thrive on convergence and divergence to ignite and keep going, and without this Invest 92L lost all of its thunderstorm activity and failed to regain it. I'm at a loss for why this happened, as 92L is over the deepest amount of Tropical Cyclone Heat Potential (TCHP), which is a measure of depth of warm water, in the Atlantic. Upper level conditions are also very favorable for development and there is plenty of moisture for 92L to work with. My conclusion for this sudden lapse in organization is due to the lack of a proper closed surface circulation that a tropical cyclone needs to survive. Looking at the current buoy data, there's no hint of westerlies on the southern side of the circulation which tells us that there is nothing on the surface and all the rotation is currently in the mid-levels. 

The National Hurricane Center (NHC) has responded in kind to the lack of organization and has lowered the percentage of genesis within 48 hours to 50% instead of 70% that it was last night. I agree with this, as 92L's only chance for development will occur in the Gulf of Mexico. The GFS and ECMWF do not further develop 92L, and show 92L either getting absorbed into an unusually strong trough for August to the north, or moving into Mexico. The statistical models are also as equally split, with the latest 1200z guidance having half of the models moving into Mexico and the other half moving into the Gulf Coast. I believe that the ECMWF's solution of a Mexico landfall is indeed the more likely, as a weaker storm would tend to ignore the weakness given off by the trough and be forced westward under a ridge being built in behind the trough. Because of this however, it's unlikely that 92L will ever amount to more than a 45kt tropical storm and is only likely to become a moderate rainfall threat. Had 92L organized properly overnight and became a tropical depression, we would have been talking about the possibility of a hurricane landfall along the Gulf Coast.

Tropical Storm Erin forms in the Eastern Atlantic
Yet another tropical storm forms by the Cape Verde islands. Invest 93L, which emerged off the coast of Africa, strengthened overnight and was revealed by last night's ASCAT pass to have a closed circulation. Based off this the National Hurricane Center upgraded 93L to Tropical Depression Five and as of the 8am advisory to Tropical Storm Erin, the fifth named storm of the Atlantic hurricane season. Erin is a well organized minimal tropical storm, with deep convection occurring over the center of circulation. Satellite shows also that Erin is beginning to separate from the monsoonal flow that it's been embedded in and has begun to move west-northwest.

The future of Erin is incredibly murky. The ECMWF correctly analysis Erin as a tropical storm, and causes Erin to move WNW into an area of high Saharan Air Layer (SAL) and the storm dies as a result. The GFS also is in accord with the ECMWF with the demise of Erin at around 120 hours while the remnant wave axis moves westward across the Atlantic. This solution appears to be identical to what we saw with Tropical Storm Dorian earlier this July. However, conditions are slightly more favorable than what we saw with Dorian. The Tropical Upper Tropospheric Trough (TUTT) has begun its climatological  retreat northwards as expect this time of year, giving way to very favorable conditions north of the islands. If Erin can remain a tropical cyclone through the forecast period, there's a chance that Erin may begin to intensify north of the islands. The other solution is that Erin continues to gain latitude and fails to bounce back towards the west as some of the global models are indicating. This would drive it through the heart of the SAL and be the nail on the coffin on Erin's life.

Further storms likely to develop behind Erin
All signs are starting to point at a period of increased activity beginning to occur behind Erin by next week. The GFS has been starting to show some consistency with emerging a tropical wave by around 69 hours and developing it into a moderate tropical storm. This wave is seen currently over Africa and will likely emerge sometime on Sunday. The GFS is having problems after that correctly figuring out what this wave will do. For whatever reason it has a 1001mb low developing to the north of the wave and causing a Fujiwara effect between the two, causing the tropical wave to somehow make landfall over Africa before re-emerging north of the Cape Verde islands and moving west. This is very unlikely, and it's more likely that this wave will develop south of the islands and continue west and strengthening. Beyond that the GFS is showing one heck of a wave train beginning to start up, and we have to start facing the possibility we may see numerous Cape Verde hurricanes beginning to set up.


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.