The tropical disturbance midway between the Caribbean islands and Africa is on the cusp of becoming the next tropical depression. A circulation is evident in the daylight satellite picture, but it’s not yet aligned with the cluster of thunderstorms. If organization continues, the National Hurricane Center will designate it an official tropical depression, and we will get a forecast cone.
From the satellite, notice the large plume of Saharan Dust that you can see surrounding the disturbance.
The disturbance is moving generally in the direction of the northern Caribbean islands. Before it gets there, however, it will have to fight off the dust, and will increasingly encounter more hostile upper winds.
As a result, the system that arrives in or near the islands about Friday is not expected to be very strong. Obviously, however, it has to be watched to be sure.
If the forecasts are right, the moisture related to the system will reach South Florida next week.
Healthy tropical disturbances are moving off Africa on schedule, but the atmosphere over the Atlantic has not been conducive for them to organize and develop yet this season.
On average, about 60 of these African disturbances – called tropical waves – emerge into the Atlantic each year. So the fact that they are there is normal.
Before the season started, the long-range computer model forecasts indicated that there would be above average development over the African continent this year. Thunderstorm complexes that start there are the seeds that become tropical disturbances when they move out over the ocean.
We are just about to enter the active part of the hurricane season. Nominally, it begins on August 20th. After that date, on average, the amount of dust over the Atlantic decreases, the ocean-water temperature nears its peak, and the atmosphere is generally more supportive of tropical development.
The National Hurricane Center publishes this graph showing the approximate number of named storms that are active on a given date over a 100-year period. Obviously, the exact number of storms per 100 years varies a bit depending on when you start and stop counting. But this is the idea.
For now, however, much of the Atlantic from Florida to Africa is covered with dry air, with the exception of a few pockets of moisture. The disturbance we’re watching is one of those pockets. Between the dry air and the somewhat hostile upper winds, the atmosphere doesn’t appear conducive for anything to else to develop through the weekend.