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 , 6:25 PM GMT on July 17, 2006
The tail end of an old cold front over the waters off the Southeast U.S. coast could serve as the focus for some tropical development over the next few days. Some impressive thunderstorms are developing over the waters due east of Georgia, thanks to a narrow area of reduced wind shear of 5-10 knots that has developed here. The GFS computer model is indicating that this reduced shear will remain for the next few days, and the Hurricane Center has scheduled a reconnaissance aircraft to check the system out on Tuesday at 2pm EDT, if needed. The system is over the warm Gulf Stream waters, where sea surface temperatures are very favorable for development, 28-30 C. The system is still pretty disorganized, although the latest visible imagery is hinting at a surface circulation. I believe that the earliest a tropical depression would form is Wednesday.
Steering currents are weak, so it is difficult to tell where this system might go. A strong trough of low pressure is expected to push off the East Coast by Wednesday, so this may turn the disturbance northwards and recurve it out to sea. However, it's quite possible the trough will not be strong enough to grab the disturbance, which will wander about off the Carolina coast for most of the week.
Figure 1. Latest satellite image of the Southeast Coast disturbance.
Figure 2. Preliminary forecast model tracks for the SOutheast Coast disturbance.
A very large area of concentrated thunderstorms is a few hundred miles northeast of Puerto Rico. This is associated with a tropical wave interacting with an upper-level low pressure system. Wind shear is 20 - 30 knots over this area, and no tropical development is expected. We will have to watch this area later in the week as it approaches the East Coast, but it appears now that wind shear will remain too high to allow development.
An extratropical or subtropical low is about 220 miles south-southeast of southwestern Nova Scotia, and is moving northeast away from the U.S. at 20 mph. The storm is over the Gulf Stream where water temperatures are in the upper 70s, which is borderline for a tropical storm. The low has a large area of heavy thunderstorms on the northeast side of the center of circulation, and is undergoing significant wind shear that is exposing the center. This storm is not a threat to develop into a tropical storm, since the waters in front of it are too cool to allow tropical development.
Figure 3. Visible satellite image for 8am EDT July 17 2006, showing the various areas of interest along the East Coast.
A solid-looking tropical wave has just emerged off the coast of Africa, and is headed towards the Cape Verde Islands at 15-20 mph. Water temperatures are marginal for tropical development in this region, wind shear is high, 10-30 knots. I'm not expecting this wave to be a threat, even though the wind shear forecast shows wind shear dropping tomorrow. It's very common this time of year to see impressive looking waves come off the coast of Africa, only to fizzle after spending a day over the water. If the wave is still holding togther by this time tomorrow, I'll take it seriously. But I think we need another two weeks for the waters to warm before these African waves will bear watching.
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