What was once a quiet tropical pattern is set to start ramping up over the next couple of weeks. A lot has changed over the past 24 hours, and it’s trending in a direction we don’t want to see.
Now, before getting into any details, I want to make sure everyone knows this: There is not any threat to the mainland US as far as we know. The systems that have the best chance of forming are out in the deep tropics, and probably won’t enter our side of the ocean for at least seven more days. The National Hurricane Center currently has only a 20-percent chance of development for one tropical wave.
With that disclaimer, let’s get into the tropics! Since there is a good deal to discuss out in the Atlantic Ocean, and Tropical Storm Celia isn’t forecast to directly impact land, this discussion is going to focus exclusively on the Atlantic basin.
Above is the infrared satellite imagery from last night. There are four systems of interest circled, and the numbers will be referenced throughout this post.
1 is Tropical Storm Celia, which we said we won’t discuss.
2 is a weak tropical wave generating storms over Hispaniola, Jamaica, and Cuba.
3 and 4 are both tropical waves moving off of the African coastline, and are both interesting enough to devote the remainder of this update to.
These are labeled the same way as Jake’s update yesterday, to avoid confusion.
This map is the GFS lower level vorticity map for the same time. Vorticity is a parameter defined by winds rotating cyclonically (counter clockwise in the Northern Hemisphere), and since tropical cyclones rotate in that same direction, you can spot potential areas of cyclone formation on a lower level vorticity map.
System 1/TS Celia has the strongest low level signature, after all, it has already formed and is currently strengthening. Area 2 is virtually non-existent, hardly more than a wind shift. Areas 3 and 4 don’t look like much yet, but they do have a lot of ocean in front of them. Area 4 already has a good amount of curvature in the wind field, but not enough to signify an already formed system. It is also associated with stronger and more widespread thunderstorms (see satellite).
Sometimes, multiple systems in a row can help the one further back. Thinking back to 2020, one of the reasons that Hurricane Laura got to be so strong, was that Hurricane Marco moved over the same area. Marco didn’t produce much adverse weather for the Gulf, but it did push dry air out of the way, leaving a more humid and better environment for Laura to follow. This is just an example of the process, so please remember:
THIS SYSTEM WILL NOT BE LIKE HURRICANE LAURA.
Any storm that comes out of this mess will not be as strong or destructive, as Laura was a very rare situation. That being said, models are starting to indicate potential development of this system, so it’s a good idea to pay attention to it.
Above are two maps – both are different models showing potential paths for our two systems. The one labeled “EURO” is the European Ensembles, and the one labeled “GEFS” is the American Ensembles. Though it seems cluttered, I have marked out the general paths for both Area 3 and 4 – the systems we’re watching.
This is NOT exactly where the systems will go, in fact, this is to show you that there is still a lot of uncertainty on where they will go, and how strong they may be.
With that being said, both models show system 3 taking a very Southerly track, potentially bringing impacts to the Venezuelan coast and Trinidad and Tobago. The models also generally show Area 4 taking a slightly further North track, which could put it in the Western Caribbean by some time next week.
The reason for this can be found in the upper levels, which are largely responsible for “steering”, or pushing storms in a certain direction. The main steering is a series of High pressure ridges across the North Atlantic, directing storms to the West.
The red line is a trough. Troughs can allow for weaknesses in the ridge, and allow for a tropical cyclone to “slip” through the ridges instead of riding along the edge. The European ensembles generally show the ridge holding up, while the American models show a stronger trough. This, in turn, is why the American model tracks start to turn more to the North. This is a super specific detail that the models will have a hard time sniffing out, which makes this all highly variable.
As far as intensity goes, both models are showing a fairly weak storm, though these global ensembles tend to do that this far out. Of all the lines on the maps earlier, only green lines are tropical storm strength or greater, and most are blue – indicating tropical depression strength. American models show a stronger system 4, while the European models don’t intensify it as much. As long as this continues, I’ll be rooting for Team Euro. I’ll talk about this difference once we go over the influencing factors.
Sea surface temperatures are a great way of looking at the heat content of the ocean, and since warm waters are needed for tropical cyclone development, we can see the areas that are the best for them. The areas in yellow have water temperatures above 26C, which is sufficient for development. Ideally, you would want temperatures closer to 29C/30C, but those won’t be found until later in the hurricane season.
Lastly, tropical storms need a lack of wind shear. The same mechanism that generates severe weather and tornadoes will rip a hurricane into shreds. As the systems approach the Caribbean, wind shear is generally unfavorable for development, largely due to that trough I showed earlier. Shear is stronger to the North, and weaker to the South, which tells us that the storms path will have a strong influence on intensity.
Generally speaking, if Area 4 can stay to the South, it will encounter warmer waters, less shear (since it’s further away from that upper level trough), and less dry air (since it can stay in the path of Area 3). This would be more favorable for development, and IF the storm can take a southern path, it would have to be watched as it enters the Eastern Atlantic.
If conditions are favorable to the South, then why does the American model show a stronger system farther to the North? After all, the American model had more orange and red lines, and less blue and green. The answer may actually be simple. A stronger storm will have taller clouds, and if they get tall enough, they can get caught in the upper level jet stream, which is blowing West to East. This can exert an eastward force on the system, pushing it further East and North.
So, with all that being said: We simply don’t know the exact track details. Look at the satellite yourself, there’s not a defined system at all to even track. This whole discussion depends on if the system develops any further at all, which there are a lot of questions about. After all, it is crucial to remember that the National Hurricane Center only shows a 20-percent chance of tropical cyclone development in the next 5 days.
One thing is for certain, something looks more likely to come out of the deep tropics than at this time yesterday, so we’ll just have to keep waiting and watching. This is a long way away from even thinking about impacting the US, so I really wouldn’t worry about too much. Just keep checking in and staying informed about the current tropical shenanigans.
