Tropical Storm Sam is expected to form today out of the Atlantic disturbance
The disturbance far out in the Atlantic is still designated Tropical Depression Eighteen, but it is on the cusp of organizing into Tropical Storm Sam. The system is in a corridor that appears prime for strengthening, which the National Hurricane Center predicts will happen over at least the next 5 days. The current prediction is that Sam will reach Category 3 strength while it is still well east of the Caribbean islands.
Sam is going to be a slow mover, so it will have an unusual amount of time over the warm tropical Atlantic. In the end, this might be a good thing. The computer forecast models have consistently predicted that Sam is more likely to turn north if it becomes a strong storm.
On the other hand, there will be more opportunity for the downstream steering pattern to change in ways we can't foresee now because Sam will have more time over the tropical ocean.
Currently, Sam is being driven toward the Caribbean islands by a high-pressure system that is sprawled across the Atlantic to the system’s north. It’s not a very strong high, however, so its steering flow is pretty weak. Thus, Sam is strolling along.
The question is, how strong is the high going to be when Sam is closer to the islands early next week? The weather pattern to the north will get more complicated.
The North Atlantic winter-like storm that formed out of former Tropical Storm Odette is forecast to drop south into the middle of the Atlantic and interact with the remnants of Tropical Storm Rose. The low pressure from this combo system will weaken the high, according to the long-range computer forecast models. That combined with higher pressure over the Caribbean is forecast to slow Sam down even more.
In addition, a big dip in the jet stream is forecast to set up just off the U.S. East Coast early next week. This is the dip that hopefully will push some dry northern air into South Florida about Monday.
If Sam would get on its horse and get going, it would run into that dip and be deflected north. That may not happen, however. Sam is moving so slowly, the dip might move on.
So the question is, what will the elements of the steering pattern be late next week. Honestly, it’s ridiculous to speculate. There are too many moving parts.
Because subtleties make so much difference in the long range forecast, and this situation is chock full of subtle factors, the various computer forecast models are coming up with a variety of long-range predictions.
For now, soon-to-be Sam is 3,000 miles from South Florida. It’s way too soon to be either concerned or not concerned. And because Sam is moving so slowly, we have a lot of time to watch it.
Tropical Depressions Peter and Rose have petered out, so to speak. Except for the contribution Rose might make to weakening the high-pressure system north of soon-to-be Sam, they are inconsequential.
If Sam forms today as expected, this will be the second soonest in the hurricane season that the “S” storm has formed. The only earlier “S” was last year when Tropical Storm Sally formed on September 12th. In the other hyper busy year, 2005, the “S” storm didn’t form until October 2nd.