Tropical Weather Update

October 2, 2020

Synopsis: I wrote a bit more than I thought I would, so here's a summary: The first system will probably develop into a tropical depression or tropical storm and *could* be a threat to southwest Texas next weekend or the following week, it could also just dissipate over land. The second system needs to be watched also but there's so much uncertainty that it might be mid week before we have a better idea what will happen, if it even develops. Outside the tropics the weather should be mostly nice and boring in the deep south through the coming week.

Here's the 5-day tropical outlook:

The northwest Caribbean continues to be the area to watch for tropical development. The area we've been watching all week now has a 90% chance of development and it is expected to become a tropical depression or tropical storm today or tonight. The future of this system is a bit uncertain. If the storm stays weak in the near term, as is expected, it will continue to move slowly west-northwest and then more westerly. If it were to somehow strengthen significantly, steering currents for a stronger storm could pull it to the northeast across western Cuba and south Florida. As I mentioned, this is not expected. If we go out a few more days to mid week what happens depends a lot on land interaction with the GFS and ECMWF split nicely between two scenarios. The GFS hooks the system to the north around the Yucatan Peninsula and into the Bay of Campeche, avoiding nearly all land interaction. The GFS then has a hurricane form that moves off towards the US/Mexico border late next week or weekend. The Euro takes the system squarely across land where it dissipates over Central America. These aren't the only possibilities but they represent the spread of possible outcomes fairly well. Regarding which will occur is uncertain and depends on where the storm center forms and how strong it is before it gets near land. There is also a front draped across the area with dry air to the north, any developing system is going to have to fight off this dry air.

The next tropical wave, now located more or less south of Puerto Rico has a 30% chance of development over 5 days as it continues west. The general consensus is that this system has the greater potential down the road but a lot of uncertainty remains. Levi Cowan of Tropical Tidbits mentioned last night that this wave could actually split with one piece going north of the Greater Antilles and another going west through the Caribbean. He called the overall situation with this "complex." The current run of the GFS doesn't develop this at all. Because it develops the first system, the outflow from that storm creates unfavorable conditions for the second wave. The Euro brings the second system into the Bay of Campeche late next week where it starts to develop, that is where the model run ends at 240 hours out. As mentioned it has the first system dissipating so favorable conditions are left behind. The ensemble guidance is a bit hard to interpret because there are many runs of two different systems in the same vicinity at the same time. The Euro ensemble has 51 members and the new GFS has 31 so with two systems there is a lot going on looking at one map. The Euro ensemble generally supports the operational model keeping the first system weak and developing the second system in the southwest Gulf. The GFS ensemble has both strong and weak solutions for the first storm so looking out mid to late next week the Gulf is a mess of potential solutions between both systems. It might be mid week before we start to have a better idea what is going to happen and we need to see what the first system does to forecast the next system.

Up here in the mid-latitudes we should have fairly benign weather through most of the coming week (assuming nothing tropical comes our way...). Near the coast we could see some rain Tuesday or Wednesday as some tropical moisture gets pulled up from the Caribbean. Temps should warm by mid week and then we may see a dip by the end of the week and possibly some rain as a front comes through. As a follow up, the last two days where there was a chance of severe weather were a bust. On 9/24 there wasn't a single storm report. On 9/28 there was one wind report in eastern Tennessee.

That's all I have for today. I'll send out another update in the first half of next week. Have a good Friday and a great weekend.

Chris