Tropical Depression Five forms

The Hurricane Hunters found a closed circulation and surface winds of 35 mph in the tropical wave moving through the Lesser Antilles, so this system is now Tropical Depression Five. Here's the 3:30pm EDT statement from NHC:

Reports from an Air Force reconnaissance plane indicate that the tropical wave moving westward through the Windward Islands has developed a closed wind circulation...and advisories on either a tropical depression or tropical storm will be initiated at 5 PM AST. Maximum winds at this time appear to be just below tropical storm strength...but it is possible that stronger winds may be observed prior to advisory time.

The new center that developed 100 miles north of the South American coast this morning is beginning to consolidate, with a new line of intense thunderstorms developing to the south of the center. This new spiral band joins the older spiral band to the east, which has brought wind gusts as high as 51 mph to the Islands today. It is clear that this will be Tropical Storm Ernesto in short order.

Current conditions in the islands
Barbados reported sustained winds of 32 mph at 5am this morning, and wind gusts as high as 51 mph. Togabo had wind gusts to 36 mph, and sustained winds of 33 mph with wind gusts to 43 mph were observed on St. Lucia. A QuikSCAT satellite pass from 6:30am EDT shows a large area of 35 mph winds to the north of the center. Radar from Martinique shows the heavy bands of rain spreading over the islands. Winds on Martinique have gusted to 35 mph so far today.

Wind shear
Upper level winds out of the west are creating about 5-10 knots of wind shear over the center, which is not significantly inhibiting development. The shear is forecast to remain low through the next five days. There is a zone of very high shear to the system's north, but it is forecast to retreat to the west ahead of the developing storm. The evolution of the shear pattern over the past 24 hours has matched what the GFS has said would happen, so this gives me confidence that the shear forecast is correct, at least for the next day. This system does have the potential to become a hurricane by early next week.

The computer models
The latest 8am EDT (12Z) computer model runs were all initialized with the old center position, and thus are unreliable. We'll have to wait until the 18Z (2pm EDT) model runs are available late tonight before we can put much stock in any of the computer model solutions. With this in mind, here is my what the latest 12Z computer models say:

The Canadian model continues to be very consistent, and develops Ernesto into a hurricane south of Jamaica, that then tracks into the Gulf of Mexico. The NOGAPS model is also consistent, assuming a more southerly track will occur with little development due to close proximity to the South American coast. This forecast is already incorrect, and can be discounted. The GFS takes a weak tropical storm across the Dominican Republic on Saturday, then into the Bahamas. The GFDL takes a strong tropical storm into Haiti on Sunday, then on a long path over eastern Cuba. On Tuesday, the GFDL has the system emerging from the coast of Cuba as a weak tropical storm and passing through the Florida Keys. The run-to-run consistency of the GFDL has been poor, and both the GFDL and GFS have not done a good job forecasting the initial track of the storm so far.


Figure 1. Current satellite image of TD 5.


Figure 2. Preliminary model tracks for TD 5.

Debby
Tropical Storm Debby remains a minimal tropical storm today, but is expected to slowly intensify in response to some warmer waters along her path the next two days. By the time Debby turns north this weekend, she could attain hurricane status. Early next week, Debby is expected to get caught up in the jet stream and die in the North Atlantic.

My next update will probably be Friday morning.

Jeff Masters