Disturbance 94L in Central Atlantic; NHC management changes

A tropical wave midway between Africa and the Lesser Antilles (labeled "invest 94L" by NHC this morning) has become a little better organized this morning, and does have the potential to develop into a tropical depression later this week. Wind shear is a favorable 5-10 knots over 94L, and shear should not be a problem for it over the next few days. The system is not well-organized, with a sloppy, elongated circulation, as seen on last night's QuikSCAT pass. This morning's QuikSCAT pass missed the storm. The system does have a major impediment to development--the presence of a large, dusty area of dry air surrounding its north side (Figure 1). Water vapor satellite loops of the region don't show any significant moistening of the region around 94L occurring, and this will have to happen before the system can develop into a tropical depression. If the storm can develop a better-organized circulation, it will be able to pump more moisture into the surrounding atmosphere and help itself out. Current visible satellite loops shows that this is not happening at present--the thunderstorm activity associated with 94L is rather weak.

None of the reliable computer models develop 94L. The system should track through the Lesser Antilles Islands on Friday, bringing gusty winds and heavy rain. I expect that the earliest 94L could become a tropical depression would be Thursday, and it is unlikely the Lesser Antilles would experience anything worse than a 50 mph tropical storm. It is more likely that 94L will still be a tropical disturbance when it passes through the Lesser Antilles.


Figure 1. Water vapor satellite image of the Central Atlantic from 8:15am EDT 8/28/07. The brown colors denote very dry and dusty air from the Saharan Desert.

Honduras disturbance
A westward-moving tropical wave is bringing heavy rains to Honduras and Nicaragua today. Due to its close proximity to land, development of this wave into a tropical depression is not expected. The wave is under 10-15 knots of wind shear. None of the reliable models are predicting that this system will develop.

Computer model update
The UKMET and GFS models are indicating the possible development of a tropical depression by Thursday or Friday off the coast of Africa. There is a large surge of moisture with at least one strong tropical wave embedded in it coming off the coast of Africa this week. This moister air should make a more favorable environment for a tropical depression to form in than the one 94L finds itself in.

Most of the models also predict a low pressure system will develop off the North Carolina coast along an old frontal boundary on Thursday. Such a development may be an ordinary extratropical low pressure system, but could make the transition to a tropical system if the shear drops low enough.

NHC management changes
Acting director Dr. Ed Rappaport of The National Hurricane Center (NHC) will continue on the job until the end of this hurricane season, NOAA management revealed yesterday. Rappaport replaced director Bill Proenza on July 9, following an extraordinary few months of tumult at NHC. Joining the NHC staff on September 4 will be a new interim deputy director--Bill Read, who currently serves as the meteorologist in charge of the National Weather Service's Houston-Galveston office. Deputy director was the post Rappaport held prior to July 9. Bill Read applied for the directorship of NHC when Max Mayfield retired, but was not awarded the job. His arrival at NHC during the peak of hurricane season will be a welcome addition, as he has considerable experience dealing with hurricane emergencies.

In an apparent effort to follow some of the management changes recommended by the independent review team that performed the snap inspection of NHC in early July (see Attachment 9 of the Senate testimony from July), a new manager of the ten hurricane forecasters has been appointed as well. Rick Knabb, who is one of the six senior hurricane specialists, will be the new manager, and will be Rappaport's backup for TV interviews during hurricane emergencies.

It is still undecided where former director Proenza will wind up, but the chairs of two Senate subcommittees investigating the matter have recommended that Proenza be returned to his former job as head the NWS Southern Region.

Next update
Tomorrow is the 2-year anniversary of Hurricane Katrina. I'll discuss my experience with blogging about the storm, and give an update on 94L and the rest of the tropics.

Jeff Masters