June 27, 2024
A long one today, but you can stop after the first paragraph if you want.
Well that changed fast... On Tuesday I mentioned that a few models were indicating the possible development of a tropical wave out in the Atlantic. For reasons I'll get into below, I was fairly confident that significant development was unlikely. This no longer looks to be the case. Now designated Invest 95L, the National Hurricane Center is forecasting a 70% chance of development over the next 7 days for a tropical wave now located a few hundred miles to the southwest of the Cape Verde Islands. It is very likely that the Windward Islands will be dealing with a tropical storm or low end hurricane on Monday. We'll have to watch it closely after that to see what happens in the Caribbean but we'll have a week or more to do so. I'll discuss a few more things below, but for now just know that we may be concerned about a storm coming into the Gulf in 7-10 days. A lot of things may change between now and then. The yellow area (Invest 94L) in the western Caribbean remains no concern.
A little history on this forecast. At the beginning of the week two tropical waves were being watched for development. The first wave had just emerged off the African coast over the weekend and the second was just moving over water. Initially the GFS was more interested in the first wave while the Euro was showing more development of the second wave, but neither were showing any strong signals for development and also no significant strengthening. That's not uncommon when models first start showing development, they typically don't go from showing nothing to high confidence of a strong storm. For this system, both models have now locked in on the first wave and are now very confident that a named storm will form over the next few days. There also may be some development from the second wave, but we need to be concerned about the lead system first.
Unofficially, there is a shorter period in the hurricane season in August and September called the "Cape Verde season." It is the time of year when conditions are right for long track storms to form near the coast of Africa and track all the way across the Atlantic. This is why I mentioned in my last update that it was a bit too early for the type of development we're seeing now, typically. While not exactly a Cape Verde storm, this system is developing farther east than we usually see this time of year, but we're really only a few weeks away from that starting to change. Below you'll see two "points of origin" maps showing the historical development locations of storms, one for late June and one for early July. We're right on the cusp of the transition when storms develop mostly in the Caribbean to the time when they develop in the main development region farther east in the Atlantic. This may be a 1-off, or maybe this transition is starting a little earlier this year, we'll see. Development this far east is still relatively rare. Also, the Caribbean, particularly the eastern Caribbean, is usually quite hostile to tropical cyclones this time of year due to high wind shear. These two factors are called climatology (or part of the many things that make up climatology), which is what we expect the weather to be normally for a given location and time of year. For both of these reasons, as well as the lack of strong model signals, I didn't expect a whole lot out of this system. It looks like I was wrong.
So what are the forecast possibilities? The good news is that the future of this system is a bit uncertain. The reason that is good is because the European ensemble has many of its 51 members forecasting a very strong storm and I really hope it is wrong. I'm hopeful because at least so far the 31 members of the GFS ensemble are not showing very many strong solutions. Weather models have biases where they tend to overdo or underdo certain features that influence the overall forecast, sometimes significantly. I don't know a lot about these, but my understanding from a trusted source is that is what we may be seeing here. The Euro has a bias that in this case may be showing more intensification and the GFS a bias that is leading to weaker solutions. That doesn't mean that these solutions should be thrown out, they represent the spectrum of possibilities with varying likelihood. Unfortunately a tropical cyclone development that will likely bring impacts to somewhere is very likely at this point. I'm hoping we'll see a middle of the road solution, with maybe (hopefully) a low end to moderate hurricane impacting the Caribbean and/or Mexico or Central America, but we need to watch for a curve to the north and perhaps a stronger storm.
There are a lot of possibilities for the track solution, but looking out a week from now it seems fairly certain that a track through the Caribbean is most likely over the next week. You can see this on the track density map below. After that the track possibilities are much broader. If one of the solutions from the Euro that shows more rapid strengthening is correct, that should cause the storm to be pulled more to the north, possibly out into the Atlantic before it can make it very far to the west. A weaker storm will stay on a more westerly track much longer. The average solution seems to be one that takes the storm mostly west for a while, with a lot of divergence after that. Right now, there aren't too many tracks that would bring the storm into the central or eastern portion of the northern Gulf, but the track is very uncertain after about 7 days.
At this point we just have to wait and see how the forecast evolves. This looks like the start of what is still expected to be a very busy year for storms forming close to this same location. I'll send out another update some time this weekend or early next week, hopefully we know more about the long term track by then.
Have a good rest of the week and a good weekend.
Chris
