At 03Z today (Tuesday night in the US), TD4 was upgraded to the forth named storm of the season, Debby. This was based on infrared and microwave satellite imagery. As of 15Z, the intensity estimate is 45kts and 1000mb. It's located about 5 degrees due west of the Cape Verde islands.
The forecast for Debby is gradual strengthening, possibly reaching minimal hurricane intensity during the weekend. The track should follow a WNW to NW course, which will momentarily take the storm over cool water (25C), but in about 3 days, will be back over 28-29C water. However, combating that increase in SST is an anticipated increase in southwesterly vertical wind shear.
Elsewhere, the tropical wave that was near 50W yesterday is still lacking an organized low-level circulation, but the mid-level circulation is located at about 11N 55W and tracking W at 15kts. It has been convectively active in bursts, and chances of formation seem fairly high by the end of the week. This is the wave that exited Africa back on August 17. If this develops, the forecast would be for a WNW track through the heart of the Caribbean, likely becoming at least a tropical storm, if not a hurricane. The next number/name on deck is 5/Ernesto.
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