The tropical disturbance we are following – officially designated Potential Tropical Cyclone Six – has moved into the Caribbean Sea on a track that will take it near or over the mountains of Puerto Rico, the Dominican Republic and Haiti. Exactly where the center of the system tracks relative to the mountains will have a lot to do with how strong it is when it reaches the Bahamas, eastern Cuba, and eventually Florida late in the week.
If the organizational trend continues, and Hurricane Hunters find an organized circulation in the system, the disturbance will be re-designated Tropical Depression Six or Tropical Storm Fred, depending on the strength of the winds. If the peak winds are at least 40 mph, it will be Fred.
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The system, whether it’s Fred or not, will be small in diameter. Mountainous terrain can completely disrupt small circulations, so when the center passes over the mountains, assuming it does, the system is expected to weaken – perhaps significantly.
A second factor that could prevent the storm from strengthening quickly is the abundant dry air wrapping around the circulation. The overall environment in and around the storm is not especially moist at the present time, and that should inhibit or at least slow development.
A possible third factor working against quick strengthening could be the upper-level winds when Fred gets near Florida. Since we’re talking about 3 or 4 days from now, the exact location and configuration of the hostile upper winds are iffy. But it’s reasonable to expect that the atmosphere won’t be supportive of a strong storm when Fred is in the vicinity of South Florida, at least.
The current thinking is that the environment will be more conducive for strengthening later in the weekend if the forecast track is reasonably accurate and the system reaches the Gulf.
This means, everybody in Florida has to be vigilant this week. Since potential-Fred is just forming, forecast errors will be higher than if it were a well-developed storm. If, for example, the center of the circulation tracks slightly farther north – along the right edge of the cone – the mountains would have less effect. If that were to happen, and the upper-level winds near Florida are less hostile, the storm that arrives in the vicinity of the state could be stronger than is currently forecast. There are still many variables in play.
The point is, it’s important not to look at today’s forecast and take it as gospel.
In the short term, the disturbance will impact the Virgin Islands and Puerto Rico later today into tomorrow, and the Dominican Republic and Haiti tomorrow into Thursday. Gusty squalls with very heavy rain are forecast over both islands, with flash flooding possible.
Then the system, whatever shape it’s in, will move in the direction of Cuba, the Bahamas, and/or Florida. The moisture associated with probable-Fred or its remnants is currently scheduled to increase a bit on Friday and then bring periods of heavy rain to South Florida over the weekend. Effects could last into next week if the system tracks into the Gulf, and the peninsula ends up on the wet side of the storm.
There are too many unknowns at the moment to be certain exactly about how Fred or its remnants will impact Florida. But at the very least, it is likely that periods of heavy rain in gusty squalls will affect some part or perhaps most of the peninsula.
Elsewhere, a disturbance is just coming off Africa, and the computer forecast models say another will come along at the end of the week. But nothing shows any signs of immediate development.