Distubance approaching the Caribbean grows stronger

A tropical wave near 11N 55W, about 400 miles east of the southernmost Lesser Antilles Islands, is moving westward towards the Caribbean at about 20 mph. Thunderstorm activity has increased markedly today in association with this wave (labeled 97L by NHC), and it has the potential to develop into a tropical depression by Thursday. The Hurricane Hunters are tasked to investigate it on Thursday afternoon. The thunderstorm activity is still pretty disorganized, and mostly lies to the west of the center of circulation, so noon Thursday is the earliest it is likely to reach tropical depression status.

Wind shear is favorable, a low 5-10 knots, but is a very high 30-40 knots just to the north, and any movement of this high shear zone to the south--or 97L to the north--might disrupt it. A large area of dry air and Saharan dust lies to the north, and this has slowed development today. The storm will spread heavy rains and wind gusts to 40 mph across Trinidad, Tobago, Grenada, and the South American coast of Venezuela on Thursday, and the ABC Islands of Aruba, Bonaire, and Curacao on Friday. Development into a tropical depression--or a tropical storm--is highly dependent on how close 97L comes to the coast of Venezuela. The southeast Caribbean off the Venezuelan coast has been climatologically unfriendly to developing tropical storms. The presence of the South American land mass so close cuts off a key source of moisture for a developing storm, and many vigorous looking disturbances and tropical storms have died here.

The computer models' take on things
The latest 8am EDT computer model runs are in. The Canadian model continues to be gung-ho, developing 97L into a strong tropical storm on Saturday, south of Jamaica. The NOGAPS model assumes a more southerly track will occur, and develops 97L Saturday once it moves off the coast of Columbia. NOGAPS then takes a weak storm along the north coast of Honduras, then across the Yucatan and into the Gulf of Mexico. The GFS assumes the storm will move further north than is reasonable, and does not develop it. I think the GFS solution can be discounted. The UKMET takes the storm along the north coast of South America, and does not develop it.

My take on things
I believe there's about a 60% chance 97L will become a tropical storm. It should come very close to developing into a tropical depression Thursday afternoon or evening. However, its close proximity to South America will probably keep it somewhere between a near-tropical depression and a 45-mph tropical storm until Saturday. If it survives into Saturday, intensification into a strong tropical storm or hurricane in the western Caribbean is possible. There may be additional obstacles to overcome by then--such as too much wind shear, or the Yucatan Peninsula or Honduras getting in its way.


Figure 1. Current satellite image of Invest 97L.


Figure 2. Preliminary model tracks for disturbance 97L approaching the Lesser Antilles Islands.

Debby
Tropical Storm Debby has deteriorated a bit this afternoon, thanks to dry air and cooler waters. Debby is expected to turn more northwestward over the weekend, and get pulled northwards and recurved into the prevailing westerly winds at high latitudes over cold waters early next week. Debby is not a threat to any land areas. The storm will be in a more favorable environment for intensification on Friday, and could eventually make it to Category 2 hurricane status, as predicted by the GFDL model.

I'll have an update Thursday morning.

Jeff Masters