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 , 8:57 PM GMT on August 22, 2006
Tropical Depression Four has increased its organization and is close to tropical storm status. It has made what is likely to be its closest pass to any land area--a brush of the Cape Verde Islands off the coast of Africa. The storm is moving towards the west-northwest away from these islands today, towards the open Atlantic. Mindelo reported sustained winds as high as 27 mph today, but no rain--just widespread dust. Other than pulling a lot of dust over these islands, the effect of the storm was minimal. The storm will provide a good case study for the NASA African Monsoon Multidisciplinary Analyses Project, which has several weather research aircraft based in the Cape Verdes Islands right now. The project aims to examine the formation and evolution of tropical hurricanes in the eastern and central Atlantic and their impact on the U.S. east coast, and the composition and structure of the Saharan Air Layer, and whether aerosols affect cloud precipitation and influence cyclone development.
TD Four is in a moderately favorable environment for intensification, and should be a tropical storm by morning. Wind shear is a low 5-10 knots. I expect this will be a Category 1 hurricane by Sunday, but it should stay far away from land. All of the models now have the storm recurving northwards well east of Bermuda early next week, as a trough of low pressure picks up the storm.
Figure 1. Visible satellite image from 2:30pm EDT Tue Aug 22 2006. TD Four is on the right of the image, just off the coast of Africa, and tropical disturbance 97L is in the left side of the image. A long line of cumulus clouds and thunderstorms nearly connects the two systems. Image credit: Navy Research Lab.
New threat approaching the Lesser Antilles
A tropical wave near 10N 47W has developed some rotation at mid levels, and is a threat to develop into a tropical depression later this week. NHC has assigned this disturbance the name "Invest 97L", and has tentatively tasked the Hurricane Hunters to investigate it on Thursday afternoon. There have been some intermittent bursts of heavy thunderstorm activity this afternoon near the center of circulation, but the cloud pattern is very disorganized at present. Wind shear is about 10-15 knots, the waters underneath are warm, and the wind shear is forecast to remain low for the next week along the system's path. The main impediment to development in the next two days will be the large area of dry air and Saharan dust to the wave's north. The system should move through the Lesser Antilles Islands on Thursday. The GFS and NOGAPS models hint at development in the Central Caribbean by Saturday, and a possible threat to Jamaica, Cuba, and Hispanolia by Sunday. We'll have to watch this system carefully, it has the potential to be trouble.
Figure 2. Preliminary model tracks for disturbance 97L approaching the Lesser Antilles Islands.
An area of thunderstorms in the western Caribbean near Cuba is drifting northwestwards into the Gulf of Mexico. Wind shear is a high 20 knots over this area, and upper level winds are not favorable for development.
I'll have an update in the morning.
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