Southwestern Caribbean Tropical Disturbance May Develop Into A Tropical System This Weekend With A Track Towards The Northwestern Caribbean Possible Early Next Week
Rob Lightbown of Crown Weather Services
October 10, 2019
Satellite imagery indicates that there is an area of shower and thunderstorm activity occurring over the southwestern Caribbean. This disturbed weather is being caused by a tropical wave interacting with the Monsoon trough of low pressure. This convection has been occurring here since yesterday morning and I do think that it’s something that requires close watching for possible tropical development over the next few days.
The area of disturbed weather over the southwestern Caribbean is in an area of favorable environmental conditions with wind shear values of 5 to 15 knots occurring across much of the southwestern Caribbean. In fact, these favorable environmental conditions are now occurring across much of the western Caribbean.
Given the favorable environmental conditions and persistent convection, I think that we will see a gradual increase in organization of this area of disturbed weather over the next couple of days. In fact, it’s possible that we will see this disturbance strengthen into at least a tropical depression this weekend over the southwestern Caribbean.
Looking at the latest model guidance – The model guidance is actually kind of interesting if you really dig into the guidance.
Both the GFS and Canadian model guidance forecasts tropical development to occur this weekend near the eastern coast of Nicaragua and Honduras. From there, they show a track that takes it to Belize by Tuesday and eventually into the Bay of Campeche around the middle part of next week. After that, the GFS and Canadian model seems to suggest land interaction with southern Mexico will lead to this system dissipating by later next week.
The European model continues to insist that tropical development will occur in the eastern Pacific rather than the western Caribbean (which is still quite possible) around the middle part of next week.
Interestingly though, the European ensemble guidance seems to suggest that the chances for tropical development in the western Caribbean are higher than the eastern Pacific. In fact, 18 percent of the ensemble members forecast an eventual impact on the US Gulf Coast late next week or next weekend.
What is a head scratcher though is that the GFS ensemble guidance is the complete opposite and shows a nearly zero chance for tropical development from this disturbance. So, is this a “bad run” of the European ensemble guidance or is it a trend towards a higher chance for tropical development in the western Caribbean?
The reason for the higher chances for tropical development that we are seeing with the European ensemble guidance seems to have to do with a trend towards a stronger eastern US trough of low pressure late next week. This leads to this disturbance being pulled northwestward rather than being pushed directly westward into Central America.
Here Are My Thoughts: I still think that there is a 50-50 chance for tropical development to occur first in the southwestern Caribbean this weekend and for this tropical system to be guided towards either Belize or the eastern Yucatan Peninsula during the first half of next week.
I still think that there is a significant amount of uncertainty as to where this system may go next week. As I mentioned earlier this week, the weather pattern across North America may undergo some significant changes over the next couple of weeks. The reason for the large changes in the weather pattern has to do with Typhoon Hagibis in the western Pacific. It is possible that this typhoon could cause a downstream trough of low pressure to develop over the eastern United States late next week and next weekend. This trough of low pressure could create a weakness in the high pressure system and pull our western Caribbean tropical system northward into the Gulf of Mexico next weekend.
Large weather pattern changes like this are not resolved well at all in the model guidance. Oftentimes, the model guidance are slow in showing these large changes. I think this is why we have seen a change in the European ensemble guidance towards a higher risk of a tropical system in the Gulf of Mexico and a stronger eastern US trough of low pressure. In fact, we are probably not done with seeing shifts and trends in the model guidance towards an eastern US trough.
So, at this point, be careful when looking at the model guidance for the next ten days or so as they may not be totally catching onto the weather pattern changes that could occur.
Why is this all important when talking about our tropical disturbance in the southwestern Caribbean?
Well, if the ridge of high pressure over the Gulf of Mexico holds strong for the next week or so, then it would push our tropical system inland into Central America and then eventually into the eastern Pacific.
On the other hand, if we do see a trough of low pressure form over the eastern United States late next week and next weekend, its influence would pull the tropical system northward into the Gulf of Mexico and towards the eastern or northeastern Gulf Coast as soon as next weekend.
Bottom line is that for the next several days or so, all of the model guidance will likely undergo large changes in how they see the upper level weather pattern. Eventually, they will “figure out” the large scale weather pattern change.
Now, if we look at climatology for mid and late October, it would suggest any organizing and strengthening tropical system in the western Caribbean would be pulled either towards the central or eastern Gulf of Mexico or across the Florida Peninsula and up the US East Coast.