Good morning! This tropical update will be similar to the other discussions, as there isn’t a ton of stuff to talk about-which is great news! After a year like 2020 or 2021, you learn to appreciate quiet in the Tropics.
Later on in this post, I have a bit of an educational segment, mostly because I have spare time since I’m writing on a Saturday night, and there aren’t any storms to talk about. Feel free to read a bit about the science behind forming hurricanes!
So, with that being said, let’s take a quick look at what’s going on in the tropics!
Looking at the satellite, there isn’t much noteworthy to speak of in the Atlantic Basin.
Out on the left-hand side of the screen, Hurricane Estelle is rapidly intensifying in the Eastern Pacific Ocean. Estelle has a pretty satellite presentation, and is forecast to strengthen into a Category 3 hurricane a few hundred miles SW of the Mexican State of Jalisco.
Just to put this in perspective, the average Eastern Pacific Hurricane Season features 4 Major Hurricanes (Cat 3 or higher). As of July 17, we’ve already seen Bonnie (Cat 3) and Darby (Cat 4) reach that criteria, and Estelle is forecast to become number 3! This is why I’m considering this July to be hyper-active, though it may not meet the official criteria.
The NOAA seasonal outlook predicted 0-3 Major Hurricanes, so that might get blown out of the water as well. It’s just very interesting to see such an active early season during a La Nina, which usually means a less active EPAC season.
Estelle is going to stay far away from any land interests in SW Mexico, and shouldn’t have much of an impact on anybody outside of boating or travel.
Former Hurricane Darby, out in the Central Pacific, passed South of the Hawaiian Islands last night, and weakened enough to lose it’s title as a tropical system. It has lost most of it’s deep convection and thunderstorm activity, so it won’t pose much more of a threat to land either.
Finally, looking out to the Atlantic, the main feature sticking out is the ITCZ. The InterTropical Convergence Zone is a region that runs across the whole length of the globe. In the summer, it moves North of the Equator.
This zone is an area where generally, the low level winds meet and converge on a line around the Equator. Once the air is forced against itself, it has nowhere to go but up, and that rising air usually leads to thunderstorm activity.
All of the storms on satellite, at around 10 degrees North, are part of the ITCZ, not a tropical disturbance. Sometimes, a disturbance can form out of this belt of activity, but right now, everything is relatively calm.
Looking at the current conditions, it’s pretty clear that nothing big is going on.
The current vorticity map, measuring the turning of the winds at around one mile in the air, doesn’t show any significant systems in the Tropical Atlantic. Looking at Estelle in the Pacific, that is a great example of the kind of signal you want to look for in a vorticity map-that shows a strong and well-defined system.
Comparatively, the meanest looking system in the Atlantic, is located around 40 degrees West, and 10 degrees N. It has a red, linear appearance, which suggests a strung out “lobe” of vorticity. When the vorticity is strung out, it’s hard to strengthen, because everything needs to be circular and more gathered up.
This is indicative of maybe heavy rain and squally weather, but nothing significant in terms of tropical development.
The main reason for the shutdown of activity in the Tropical Atlantic is a lot of Saharan dry air.
The relative humidity map for this morning shows a huge mass of dry air across the Northern Atlantic. Compare the conditions around the Atlantic system to what it looks like on the SW Mexican coast- Estelle has a huge, expansive “bubble” of moist air, while the ITCZ storms in the Atlantic are exposed to lots of dry air, inhibiting any growth or development.
The shear across the Atlantic has actually relaxed quite a bit over the last few days, with more reasonable values across the Central Atlantic.
But, a large upper level trough (sometimes called a TUTT, or Tropical Upper Tropospheric Trough) is imparting a lot of wind shear over the Caribbean Sea, and would shred any forming systems that moved into the area.
Another piece of good news is the major ridge about to set up over the Southern 2/3 of the US this upcoming week-Although the heat it is going to generate is going to suck, it will do a great job steering any potential tropical cyclones away from the US.
Not that anything is even likely to form in the area, but should something pop up over these last 2 weeks of July, it is more likely to pass well to our South here in the Mainland US.
One signal over the next 4 days has been for a potential weak tropical cyclone to develop in the SW Caribbean, which could bring nasty weather to Northern Panama, Costa Rica, and Southern Nicaragua.
Like many of the potential systems we’ve seen this season, this is just a small handful of computer guidance, and it isn’t being monitored by the NHC. If anything comes out of this (which is very unlikely), it will be weak and short-lived, though it’s remnants may spark a new system in the Western Pacific, which has been hyper-active this July.
Honestly, if you were to take an industrial fan in Costa Rica and turn it towards the Pacific, it would probably generate enough energy to form a Hurricane. The Eastern Pacific Hurricane Season has been insanely active, and is forecast to stay that way.
A couple of members of the American computer model ensembles do throw a weak tropical depression into Central America, but we really shouldn’t have anything to worry about here, aside from some inclement weather towards the middle of this week.
In the upper levels of the atmosphere, there is converging air (coming together) above the potential system. When air converges at the surface, it has no place to go but up. At the top, the opposite is true, and air is forced to sink.
The 200 mb (usually around 7 miles above the ground) wind flow suggests that air is going to be piling in from all directions over our system, which is ultimately going to hurt it before it has a chance to develop.
Some of the Science Behind Hurricanes
So, earlier in the post, I mentioned that convergence can help thunderstorms form, but now I’m saying it kills thunderstorms. This might seem contradictory, but there is a reason for this, and this section might help you understand why this happens, as opposed to me just saying it will. Be warned, this is educational!
One crucial reason is actually a main quality of air-that when it sinks, it dries. Basically, and there are a lot of simplifications here, the atmosphere follows a pattern like this:
When there are lots of thunderstorms forming, they can work together to lower the pressure inside of a storm, which actually creates a “positive feedback loop”, where thunderstorms help lower the pressure, which causes air to rise and thunderstorms to form, which lowers the pressure, and so on.
Lower pressures also lead to higher winds in the storm system, and stronger winds can increase the atmospheric moisture content, since rough waves whip up really small water molecules, which generates more thunderstorms, and I bet by now you can see how things can get out of hand in really good conditions.
In addition, there is a second positive feedback loop caused by thunderstorms, if you’re still reading. Since thunderstorms turn a lot of water vapor into a liquid, there is a lot of heat released. Water loses heat when it condenses, and the heat has to go somewhere, so it warms the air around the water. That warm air rises in the center of the storm (which is why stronger hurricanes have eyes), and when it hits the top of our atmosphere, it flattens and spreads out in all directions. This is known as “outflow” since it’s leaving the storm. Very strong outflow can disrupt the jet stream pattern, and create a protective bubble around a storm. This “bubble” can do a decent job keeping the stronger wind shear away from the center of the storm, and helping the organization of a system. Increased organization will lead to more active thunderstorm development, and guess what, we’re right back at the beginning!
These are two ways that show how tropical storms can strengthen, until something disrupts the cycle. Obviously, not every disturbance grows and strengthens, so it takes just the right conditions early on. Strong wind shear will disturb the organization of the system, preventing it from establishing a center. Low humidity will suck the water out of the thunderstorms, and stop the process from happening. Without warm waters, there’s no instability, and the air isn’t warm enough to rise and produce storms. This is why in the early stages of a tropical system, everything has to be just right to get something big.
Well, I hope you at least learned something on this easy-going Sunday! Until something else interesting happens, I don’t have too much to talk about, so it’s a good time to learn a bit about the why, not just the what. Take care!
