Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 3:20 PM GMT on August 26, 2006
The Hurricane Hunters found a strengthening Tropical Storm Ernesto this morning. Their final report at 5:30am EDT had a pressure of 997mb, good enough for 50 mph winds at the surface. Water vapor satellite loops show a large upper level low forming over the western Caribbean, and this low is moving westward at nearly the same speed as Ernesto. Counterclockwise flow of air around the upper low is causing 15-20 knots of shear over Ernesto, and this can be seen in the water vapor loop and visible satellite loop causing a flattening of the clouds on the west side of the storm. However, the overall appearance of Ernesto on satellite imagery is slowly improving, with upper-level outflow developing on the east side, and more low-level spiral bands forming. Long range radar animations from Puerto Rico show these spiral bands. Rain amount of 1-3 inches have fallen across the island so far today, with isolated totals as high as 8 inches. As long as Ernesto does not grow any closer to the upper level low to his west, slow intensification should occur the remainder of today.
As Ernesto passes south of Haiti today, the mountainous southwestern peninsula could experience life-threatening flash floods. This is common in this part of Haiti, even for modest tropical storms. Deforestation of the hillsides has left them little protection from floodwaters.
Figure 1. Current storm total rain in Puerto Rico.
The intensity forecast
The latest 06 GMT (2am EDT) model runs are in, and they again portray a conflicting picture of what may happen. Two of the four major global models--UKMET and GFS--dissipate or severely weaken the storm by Monday. However, the other two major models, the NOGAPS and GFDL, foresee a major hurricane in the Gulf that hits the Florida Panhandle on Friday. The Canadian model takes a major hurricane to the Louisiana coast on Friday. It appears that the two models poo-pooing Ernesto--the UKMET and GFS--are not doing a good job initializing the storm, and this is causing an overly optimistic weakening. Ernesto is holding his own again the shear, and is much stronger today than these models were predicting in their runs yesterday. The NHC official forecast of a continued slow intensification into a Category 1 hurricane by Monday seems like a reasonable one. After that, an explosive deepening phase into a major Category 3 or 4 hurricane is certainly plausible, given the very warm waters and low wind shear forecast to develop. However, keep in mind that our computer models are very poor at forecasting the behavior of upper-level lows in the tropics, and the upper low to the west of Ernesto could easily be in a different location and bring significant shear to the system. In addition, intensity forecasts more than 48 hours out are very unreliable. Witness some of the intensity forecasts for Debby made two and three days ago, which called for her to be a Category 1 or 2 hurricane today. Today, Debby is a tropical depression on the verge of dissipation. With all that said, I believe that Ernesto will be a major hurricane in the Gulf of Mexico at some point.
Jamaica, the Cayman Islands, and Cuba are going to get a pounding from Ernesto as he approaches hurricane strength Sunday and Monday. Washed out roads, downed power lines and trees, and minor roof damage will be common in those islands. Ernesto is under too much shear and does not have enough time to intensify into more than a strong tropical storm or weak Category 1 hurricane before affecting those islands, and the full force of Ernesto is likely to be reserved for the U.S. Gulf Coast. Those of you with plans to be in Cancun or Cozumel can expect a day or so of airport closures due to high winds between Monday night and Tuesday night.
The track forecast
As Ernesto crosses into the Gulf of Mexico on Tuesday, a trough of low pressure will be swinging across the eastern U.S. and should pull the storm on a more northerly track. Most of the models are showing that this trough will be strong enough to bring the storm all the way to the coast between Louisiana and the Florida Panhandle. However, the trough may not be strong enough to do this, and Ernesto could get stuck in the Gulf for a week, potentially heading westwards towards Texas as a new ridge of high pressure builds in. A subsequent trough could then turn the storm northwards into the coast at some later time. The UKMET model and GFS model prefer this solution. At this point, there is not enough information to say which solution is most likely, and residents from Texas to the Florida Keys need to be prepared for this storm to affect them.
The next system?
A large tropical wave with plenty of spin came off the coast of Africa yesterday is is currently over the Cape Verde Islands. Some of the computer models forecast that this wave will develop, but this is very unlikely for at least the next three days. The Saharan Air Layer analysis is showing a large amount of dry air spiraling into the center of this wave. There are currently no other threat areas to be concerned with. In the long range, the GFS is forecasting a very busy first week of September, with two or more tropical storms developing between Africa and the Lesser Antilles.
Hurricane Ioke in the Central Pacific underwent an eyewall replacement cycle and is now a Category 4 hurricane with 150 mph winds today. However, now that this cycle is complete, the storm should attain Category 5 status again today. It's not a threat to any land areas, but if it remains a Category 4 hurricane or higher the next four days, as forecast models are calling for it to do, it might set a world record for the longest-lived Category 4 or higher storm. The 6Z GFDL model run has Ioke at 875mb in 4 days, the lowest forecast pressure ever made by the GFDL model. However, bear in mind that the GFDL model in the Central Pacific is not being run with its full coupled ocean model, so these extreme forecasts of Ioke's intensification are probably overdone. The GFDL is not the only model having trouble with Ioke--the 11pm discussion last night from the Honolulu Hurricane Center noted:
Big issue with the track guidance for the 06z model suite is that the UKMET track bounced off the date line...resulting in an erroneous mirror image track...eastbound back into the central Pacific. This threw all of the consensus model tracks off...bending them back sharply eastward.
Our tracking map software had a similar problem, and we're using some older software that doesn't have that problem right now for Ioke.
Figure 2. Visible satellite image of Category 5 Hurricane Ioke, 2030 GMT 8/25/06. Image credit: Navy research Lab.
The next Hurricane Hunter mission into Ernesto is at 2pm EDT this afternoon. I'll have an update sometime between 3-7pm today.
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