Dr. Jeff Masters' WunderBlog (1:20 PM EDT on August 28, 2008)
It's time to get familiar with the names Hanna, Josephine, Ike, and Kyle, because the tropical Atlantic is about to put on a rare burst of very high activity in the coming weeks.
Figure: Visible satellite image from 7:30 am EDT Thursday August 28, 2008. A long line of impressive tropical waves is lined up over the Atlantic and Africa. Image credit:
U.S. Navy.
Elsewhere in the tropicsMost of the computer models forecast the development of at least one additional tropical wave between Africa and the Lesser Antilles Islands during the coming week. The first candidate is a large circulation located near 18N, 39W, 800 hundred miles west of the Cape Verde Islands. While the circulation of this system is impressive, the system is devoid of any heavy thunderstorm activity, and is surrounded by a large are of dry air to the west and north. Wind shear is a moderate to marginal 10-20 knots in the region, and forecast to remain in the moderate to marginal range for the next few days. NHC is giving this system a low (<20% chance) of developing into a tropical depression by Saturday. Some slow development is possible over the next few days, but the system has a better chance 3-5 days from now, when its environment will be moister. Several of the models develop it, and predict the system will be a few hundred miles north of the northern Lesser Antilles Islands by Monday Tuesday. Like the ocean, the atmosphere also has waves. Large-scale atmospheric waves form over Africa during the African summer monsoon season, track east to west, and emerge over the Atlantic Ocean near the Cape Verde Islands, where they often serve as the nucleus for a powerful Cape Verdes-type hurricane. Well, the African Easterly Wave Factory is exceptionally busy right now, and there are three very impressive looking waves with plenty of spin lined up across the continent (see figure).
The western-most wave, just coming off the coast of Africa today, is particularly impressive. This system has a very large circulation with plenty of spin, and is already developing some concentrated heavy thunderstorms over the waters south of the Cape Verde Islands. This morning's QuikSCAT pass saw winds of 50 mph near the heaviest thunderstorms. Wind shear is a moderate 10-20 knots over the storm, and is expected to remain in the low to moderate range the next few days. NHC has given this system a medium (20%-50%) chance of developing into a tropical depression by Saturday. The models have been very aggressive developing this system over the past few days, and chances are good that this system will become a large and powerful Cape Verdes-type hurricane next week. It is too early to speculate whether this storm might end up recurving out to sea or not.
The other two waves lined up behind the wave moving off the coast are also likely to be a threat to develop once they move offshore Africa next week. The long-range GFS model develops all three of these waves.
Jeff Masters
