Hurricane Michael - 10/01/18 02:04 PM
Satellite imagery indicated that there are some scattered shower and thunderstorm activity occurring across the southwestern Caribbean to the south of Jamaica. This is being caused by a trough of low pressure located over the central Caribbean that is pushing to the west. The western half of the Caribbean will need to be watched very closely for possible tropical development later this week and this weekend.
Even though we already have convection occurring across the southwestern Caribbean, the environmental conditions across much of the Caribbean is unfavorable for development. Wind shear values across much of the Caribbean are between 25 and 40 knots. The exception is across the far northwestern Caribbean where wind shear values are between 10 and 20 knots. So, tropical development seems unlikely for at least the next couple of days.
Beyond this, the tropical development chances may increase as energy from the trough of low pressure now over the central Caribbean builds up and combines with moisture across the western Caribbean. The big question is where exactly this possible tropical development occurs and whether environmental conditions will become favorable for development.
The model guidance are unanimous in forecasting some sort of tropical development to occur across the western Caribbean beginning late this week. With that said, each individual model continues to have different scenarios of what might occur late this week through this weekend and beyond.
The GFS model forecasts that tropical development may occur as soon as this weekend across the northwestern Caribbean. By next week, however, the GFS model forecasts that the energy with this system will split and head northeast towards the Bahamas with the model showing 3 separate low pressure centers. I think the GFS model may be suffering from its bias of convective feedback as well as its bias of pulling tropical systems too quickly to the north.
The Canadian model is much more consolidated with its tropical development forecast. It shows a low pressure system to develop over the northwestern Caribbean this weekend and forecasts it to move north-northwestward into the southeastern Gulf of Mexico during the early part of next week. By next Wednesday, the Canadian model forecasts this tropical system to be located over the southeastern Gulf of Mexico as a moderately strong tropical storm.
The European model forecasts that a low pressure system will form in the northwestern Caribbean late this week and this weekend. During next week, the European model seems to suggest that part of the energy of this system will be pulled to the northeast forming a new low pressure system near the US Southeast Coast while the original one dissipates. Ultimately, the European model forecasts
Looking at the various ensemble model guidance:
The GFS ensemble model guidance are strongly pointing towards tropical development to occur just west of Jamaica around Friday and Saturday. The ensemble members split by early next week with some of the members forecasting a track towards the southeastern Gulf of Mexico and other ensemble members forecasting a track towards the northwestern Bahamas. Beyond this, the ensemble spread is pretty large with a few members forecasting an eventual landfall on the western Gulf Coast around October 14, a few members forecasting either a northern Gulf Coast or Florida Peninsula landfall between October 12 and October 14 and a few ensembles showing a track near the US Southeast Coast.
The European ensemble guidance is forecasting up to a 45 percent chance for tropical development somewhere between Jamaica and Belize this weekend. Ultimately, the European ensemble guidance member spread is large, however, it is not as large as the GFS ensemble guidance. Some of the European ensemble guidance members forecast a landfall along the northern Gulf Coast between southeastern Louisiana and the Florida Panhandle on October 11. Other European ensemble members forecast a landfall somewhere on the Florida Peninsula between October 10 and 12 and then a track up the US East Coast.
Here Are My Thoughts: Tropical development over at least the next 2 to 3 days is highly unlikely due to unfavorable environmental conditions in the Caribbean. Beyond this, I am going with a 40 percent chance for tropical development in the western and northwestern Caribbean between about Friday and Sunday. A few factors may combine to lead to the development of a tropical system in the western and northwestern Caribbean very late this week and this weekend.
The first factor is the energy and moisture from a trough of low pressure now over the central Caribbean may build up this week over the western Caribbean.
The second factor is a piece of energy from Tropical Storm Leslie may break off and head southwestward into the western Caribbean by late this week which will add to the energy and moisture.
The third factor is a upper level ridge of high pressure is forecast to strengthen over the northeastern US and Mid-Atlantic States this weekend which will naturally lower barometric pressures from the Bahamas to the western Caribbean.
I do think, given the combination of all of the factors listed above, that we have a pretty good chance of seeing a tropical depression or tropical storm form in the western and northwestern Caribbean late this week and this weekend. As I already mentioned, I’m going with a 40 percent chance for this to occur.
The next question is where could this potential tropical system head. I think given the forecast weather pattern of a large upper level ridge of high pressure over the Northeastern United States that a track towards the northeast or east-northeast towards the Bahamas and out into the open Atlantic seems unlikely. Instead, a track to the north or northwest into the Gulf of Mexico seems more plausible given the weather pattern. This means if anything does form in the western and northwestern Caribbean this weekend, the northern and eastern Gulf Coast from Louisiana to the Florida Peninsula could be threatened by this system between October 11 and October 14.
Bottom line is that this potential western and northwestern Caribbean tropical system will be watched very closely, especially as we get into late this week and this weekend.
For more information, check the daily Tropical Weather Outlook, click here.