Northern Gulf Tropical Development Is Looking More Likely Between Wednesday & Friday: The latest satellite imagery indicated that there is a concentrated area of thunderstorms located offshore of Florida’s East Coast. This convection is associated with a low pressure center now located about 150 miles to the east of Jacksonville.
Analysis reveals that there is about 10-20 knots of northeasterly wind shear that is displacing the thunderstorms just to the south of the main low pressure center.
It is expected that this area of disturbed weather will move westward across the Florida Peninsula as we get into tonight and Tuesday. A ridge of high pressure to the north of the disturbance will continue to guide this system westward across the northeastern and north-central Gulf during Wednesday and Thursday. Once it reaches the north-central Gulf, the forward speed of the disturbance may slow way down as we get into Friday and the weekend. This slow-down in forward speed or even complete stall could lead to some big problems in terms of heavy rain induced flooding across southern and southeastern Louisiana and southern Mississippi late this week into this weekend.
As for development possibilities, the environment across the northern Gulf is expected to be at least somewhat favorable for development. This means that this system does have a decent shot of developing into a tropical depression or even a tropical storm as it heads westward across the northern Gulf between Wednesday and Friday.
Latest Model Guidance: The global model guidance such as the GFS and European models continue to be very tepid in their forecast of development of this system. The reasons why they seem to not show any sort of development looks to be due to marginally favorable environmental conditions and interaction with land.
One model that continues to show significant development is the ICON model. It should also be noted that the ICON model has been the most consistent in forecasting development of this disturbance. The latest 12Z run of the ICON model forecasts the disturbance to cross the central Florida Peninsula on Tuesday and then begin to develop into a depression in the northeastern Gulf by Wednesday. From there, the ICON model forecasts this system to strengthen into a tropical storm in the north-central Gulf by Wednesday night into Thursday and then approach hurricane strength as it comes ashore in southeastern Louisiana late Thursday.
I did want to mention again that the ICON model has been pretty accurate in the Gulf with its forecast of tropical systems over the last couple of years. In fact, the ICON model was one of the only models that correctly forecasted Hurricane Beryl would impact Texas last July. So while the ICON model hasn’t been perfect in its forecasts, it has been first in showing the development of tropical systems, well before the other global models.
The GFS ensemble model guidance have only one or two members that show development in the northern Gulf later this week. So, most of the GFS ensemble model members forecast no development at all.
The European ensemble model guidance is also very shy in forecasting development as it only has 3 members forecasting development in the north-central Gulf later this week.
Here Are My Thoughts: I think that there is a very decent chance that the area of disturbed weather will become a tropical depression in the northeastern Gulf on Wednesday and then very probably become a tropical storm before it comes ashore in southeastern Louisiana late Thursday.
A couple of thoughts – First is that even though northeasterly wind shear is affecting the area of disturbed weather, the amount of deep convection that is occurring is quite healthy & is a sure sign of development.
Second thought is that the low pressure center is much more organized than what the global model guidance such as the GFS and European models show. This means that I think that these two models are not correct in their forecasts. In fact, it’s not out of the question that this system becomes a tropical depression before it crosses the Florida Peninsula.
One other thing to keep an eye on is how far south the low pressure center moves before it begins moving westward. If the low pressure center can cross the Florida Peninsula south of I-4, it would have more than enough time in the Gulf to become a fairly robust tropical storm before reaching the Louisiana coast late Thursday. On the other hand, a further north crossing across the Florida Peninsula north of I-4 would limit how much time this area of disturbed weather has over the Gulf leading to much less in the way of development.
Now, I do think that the ICON model is way too aggressive in its intensity forecast of this disturbed weather. I also think that models such as the GFS and European model are incorrect in not forecasting any sort of development.
This means that I think that there is at least a 80 percent chance of this disturbed weather becoming a depression in the northeastern Gulf Wednesday afternoon or Wednesday night. I also think that there’s a better than 50 percent chance that this system will then go on to strengthen into a 40-50 mph or so tropical storm by the time it comes ashore in southeastern Louisiana late Thursday afternoon or Thursday evening. I do think that there will be enough northerly to northeasterly wind shear over the Gulf to prevent this system becoming a hurricane. That said, it is expected that the disturbance will slow way down in forward speed just as its reaching southeastern Louisiana & given the very warm waters of the north-central Gulf, any let up in the wind shear could lead to more strengthening than what I’m thinking right now.
Heavy Rainfall Threat: Right now, the main threat from this system will be heavy rain with the risk for flash flooding, both across the Florida Peninsula the next couple of days & then across southern and southeastern Louisiana, southern Mississippi and southern Alabama later this week through this weekend.
For the Florida Peninsula – Given that most of the heavy rain is occurring to the south of the low pressure center, it seems likely that Central and South Florida will see the highest rainfall totals over the next couple of days or so. Rainfall totals of 3 to 6 inches with locally higher amounts can be expected along and especially south of I-4 with 1 to 3 inches of total rainfall expected north of I-4. These rainfall amounts will likely lead to localized flash flood issues, primarily across Central and South Florida where the highest rainfall amounts will be.
For Southern & Southeastern Louisiana, Southern Mississippi & Southern Alabama – As this system tracks westward across the northern Gulf between Wednesday and Friday, it is expected to bring heavy rainfall across southern and southeastern Louisiana, southern Mississippi and southern Alabama beginning on Wednesday night and Thursday and continuing through Friday and possibly all of this weekend. I do have serious concerns that this system could bring significant amounts of flash flooding across southern and southeastern Louisiana and southern Mississippi due to the potential for it to slow way down or stall once it reaches southeastern Louisiana. This is something that will need to be watched extremely closely.
The next tropical weather discussion will be issued on Tuesday.