The tropics continue to heat up, as we continue to monitor some disturbances in the early stages of the Atlantic Hurricane Season. Get buckled in, because this is gonna be an in-depth discussion for all things tropics.
First, let’s look at the current conditions before breaking down each item of interest individually.
Going from East to West, we have a few notable things we want to pay attention to.
Above is the 850 mb vorticity, which measures the curvature in the low-level wind, which can help detect potential disturbances. The infrared satellite is also posted, which shows the intensity of thunderstorms associated with the disturbances.
Disturbance 1 is an African tropical wave coming off the coast of Africa. Some development of this wave is possible in the future, and models are now starting to pick up on it’s development into next week.
The red circle labeled 94L is what’s called an Invest, or investigative area. Invest 94L currently has a 70-percent chance of developing in the next 5 days, and needs to be monitored as it approaches the Caribbean Islands and the South Caribbean Sea. It also has a 40-percent chance of formation in the next 48 hours, per the 1am NHC update.
Disturbance 2 is a weak tropical wave approaching the Windward Islands, but is not likely to develop. In past updates, it looked like it may have had a chance to develop, but that has become much less likely in the past few days. I won’t be going into much detail on this.
Disturbance 3 is associated with a frontal system passing through the Southeast US, and is about to detach and stall in the gulf of Mexico. The NHC gives this a 20-percent chance of developing over the next 5 days, and should be monitored as it meanders West towards the Texas coastline.
As has been the case, I will refer to these storms given the numbers above – Invest 94L, and disturbances 1, 2, and 3.
Lets start to take a look at the current conditions across the Atlantic Basin.
We like to show Sea Surface temperatures a lot, but for the deep ocean, a better tool to use to look at the potential energy from warm waters is called OHC, or Ocean Heat Content. OHC, in a really basic sense, measures how hot the water is, and how deep the heat stretches. If the water on the surface of the ocean is very hot, but cold a few dozen meters below the surface, then rough waves can cool off the waters very fast by mixing the cold and hot water together.
But, if there is a deep warm layer, it is harder to cool off that water. That’s what the OHC is looking for.
Yesterday’s OHC shows that most of the Atlantic isn’t super hot. The light blues and yellows indicate that there is probably enough heat energy for development, but it’s still very early in the season. That map will look a lot brighter in 2 months.
One thing that’s worth noting is how much more heat the Caribbean has. This is typical, and more or less expected. The Caribbean sea usually has some of the hottest waters in the Atlantic Ocean, which is one reason that this area is so heavily favored for development in the early season.
What does this tell us? It means that the storms out in the far East Atlantic don’t have nearly as much energy to work with, and probably won’t develop super fast. In the 3 days since I wrote my last update, not much has changed for 94L. But, once it hits the Caribbean Sea, it may start to strengthen a little bit faster than it has before.
The same is true for Disturbance 1. It’s in pretty cool waters right now, so there isn’t much of a threat for strengthening during the next few days. Once it progresses further West, this may start to change.
Speaking of hot waters, it’s definitely worth looking at the Gulf of Mexico right now.
OHC doesn’t work as well in the shallow waters of the Gulf Coast, so I’m going to switch back to the Sea Surface Temperature map for this one. Just a reminder, tropical storms really need to have waters above 26C. 28C waters are very conducive for development, and when you hit 30C, even more so. Check out the color table. In this map, even the blue colors are supportive of tropical storm development. Basically, the entire Gulf of Mexico is more than warm enough to support a tropical system.
The water up by the Louisiana coast might as well be bathwater, reaching around 32C / 90F. Let’s not get carried away, there is way more than one factor for storm development, but we should definitely keep tabs on Disturbance 3 for this reason. After all, it’s going to be moving across some of the hottest water on this half of the planet. I’ll get into some of the reasons why this system may not form or strengthen, but the Gulf temperature is the strongest signal for development.
Wind shear is another huge factor. This next chart has a lot of info on it, but we’ll break it down here.
The coloring on the map represents wind shear. That will kill a hurricane, so it’s important to have low amounts of it. Ideally less than 20 kt, which is colored in black, blue, or green. The yellows and reds are areas which are unfavorable.
This map also shows how the shear is changing with time, over the last 24 hours. The white circles show areas where shear is increasing, and the blue dashed circles show areas where shear is decreasing.
As Invest 94L tracks towards the West, it will encounter an area of high shear over the Lesser Antilles which may inhibit development temporarily. But, right past that, there is an area where shear is actually decreasing pretty significantly. That indicates that the areas in the South Caribbean Sea is becoming more favorable for tropical storm development as we speak. It honestly does look like this system will have pretty good conditions over the next few days.
One negative is that the unusually strong trade winds over the Caribbean Sea will give 94L a fast forward motion. That means that even though the winds aloft haven’t changed, the system will “feel” more shear than a system otherwise would, which could hurt it’s development. A good recent example of this is Tropical Storm Bret in 2017, which moved at speeds close to 30 mph!
Disturbance 1 is in a similar boat, except you can see that shear is pretty relaxed over the Eastern Atlantic. It will move into a more hostile environment soon, and this is another reason why any formation will probably have to wait.
As for Disturbance 3, it’s in a pretty good area of low shear as well. It may be ramping up ever so slightly, but it’s not too strong right now. The ridge of High Pressure over the Southern United states is going to help keep the shear relatively low, so this system won’t be getting ripped apart like early systems can sometimes tend to do in the Gulf.
Everything seems to be really favorable for tropical development. Is there going to be anything that might limit these systems?
Yeah, of course there is. Let’s look at the relative humidity values.
Wow, that is a lot of dry air out there.
Disturbance 3 is currently located in an area of high moisture, but a lot of the Gulf of Mexico is very dry. Large scale ridging supports sinking air. When air in the atmosphere sinks, it warms, and it loses some moisture. That’s why a very large portion of the Tropical Atlantic is looking pretty dry.
I consider this dry air to be the main reason that Disturbance 3 may not develop or amount to much. It takes a while for tropical systems to fully saturate their environment. Once that happens, they can travel in their own “bubble” of moist air, blocking out influences from their surroundings, but that won’t be possible for a weak system surrounded by dry air so close to the coast. This is usually a feature seen in strong hurricanes that effectively control their own environment in what’s known as a positive feedback loop.
Looking back at Invest 94L, you could say a lot of the same things about it’s environment. The Atlantic and the Caribbean are pretty dry right now. There is a difference though, and it’s one that I’ve mentioned before. Disturbance 2 is not likely to form into a tropical system. But, one thing it will do, is moisten the environment ahead of 94L, making it much more conducive to strengthening. That’s happening right now, as 94L is traveling in a plume of higher moisture behind the disturbance. This is likely to continue, and the environment probably won’t be too terrible moving forward.
As for Disturbance 1, it has a long way to go before really getting into the favorable areas. It has a lot more distance between itself and the system ahead of it, so the dry air is probably much more likely to infiltrate this system.
So, what does the future hold?
For this section, I’m going to break it down between the 3 main systems, and give my thoughts on each one.
Invest 94L
Invest 94L has the best chance of formation of all of these systems, both in the short and medium term. This storm seems to have the best combination of parameters, and definitely doesn’t look too bad as it moves to the West. Let’s look at the potential track and see what we can learn.
The upper level flow is going to push this storm to the West. As I’ve mentioned before, a stronger storm is going to deviate to the North, since it’s going to stretch higher in the atmosphere and feel the force from the jet stream aloft. The practical implications of this is that if the storm begins to rapidly intensify more than we expect (Which is unlikely, to be fair), then we should see the track shift further North. Probably not North enough to get it into the Gulf of Mexico, but still further North.
It currently looks like this storm will bring some strong storms, gusty winds, and rough surf to the Windward Islands, the Leeward Antilles, and the Northern Venezuelan/Columbian coast. There is a potential for it to strengthen in the Caribbean, before potentially bringing impacts to Nicaragua and Honduras. A stronger storm that deviates to the North may impact Belize or the Yucatán Peninsula of Mexico.
These track details are variable and not set in stone, but it appears that this is the most likely scenario.
As far as intensity is concerned, it should be made clear that intensity is by far the hardest part of hurricane forecasting, and this is usually the least accurate aspect of it. But, there are a decent number of models that bring 94L to close to hurricane strength by Wednesday or Thursday, as it moves into the open waters. This storm has decent potential to become a hurricane, but there are certainly limiting factors.
Disturbance 3
Since this storm has not been classified as an invest, there aren’t the same kind of detailed track maps. If we zoom in to the Gulf, we can see some semblance of a track idea.
These are the European Ensemble members, showing the potential track. You’ll notice that many of them are very short, because not every member of this model thinks there will be a storm. The development chance is only at 20% right now. But, if a system does develop, it will probably be weak and short lived. This cluster of tracks indicate that there is a lot of uncertainty here, so don’t latch on to this map. Just use it to know that the storm may drift to the West.
There may be enhanced rain across portions of the Texas and Louisiana coastline through the middle of this week, but realistically speaking, this storm isn’t super likely to cause major impacts. Given the hot ocean waters, we can’t ignore this completely, and should stay updated with the NHC forecasts. Impacts can arise from unorganized systems, so whether or not this is named, there may be a flooding threat. The “strength” or category only tells you a small bit about a system. In these weaker tropical scenarios, a Flash Flood Watch is just as serious as a Tropical Storm Watch.
Disturbance 1
This is the farthest from land, and doesn’t warrant a ton of concern right now. The only reason it’s in the discussion so much, is that the American model ensembles started to pick up on some strengthening later into this week, and I wanted to make sure it was covered in some capacity.
This is forecast to follow a very similar path to 94L, but there are more roadblocks preventing it’s strengthening. The NHC does not have this system set for any development, so this is just something to keep an eye on. This is very far away from potentially impacting land. There is a reason that we don’t usually see deep tropical systems develop in June-the environment is very harsh for development.
As always, please follow your National Weather Service office and the NHC for official advice, but thanks for reading my deep dive into the Tropics! More great interns are gonna pick up on these starting Tuesday, so keep tuning in for more on the latest!
Great thorough explanation of the tropical activity.