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The tropical Atlantic is still in a lull state today. However, there are two areas that captivate me this afternoon.

Southwestern Caribbean

Numerous showers and thunderstorms activity located in the southwestern Caribbean enhanced by a weak area of low pressure near the Florida Keys has gotten better organized this afternoon. This system has failed sustain itself over the past couple days, as its thunderstorm activity increases during the daytime hours and decreases overnight****1. This primarily because, the atmospheric pressure around it is too low to support its lower level convergence and upper level divergence, which are momentous necessities for tropical cyclone development. Look at the 12z sea level pressure map. You will notice that there is no anticyclone nearby to support its lower level convergence, and that is the way it has been over the past few days. Nevertheless, a dynamic anticyclone is expected to build over the eastern U.S. about 72 hours from now. This will provide a more favorable environment for this system, and we may see possible tropical cyclone development indicated by NAM model.

Brief Tutorial

You may wonder why I said that “anticyclones help provide better lower level convergence”, since most people say that “anticyclones help provide “upper level divergence”. Yes, that is correct, but technically, an anticyclone helps provide better lower level convergence, which in turn provide good upper level divergence.

Let me explain how this works.

Air flows from an area of high pressure to low pressure (one of the most fundamental laws in weather). To give you a vivid imagery of this, imagine a bathtub where water is sinking into a draining hole, you will notice that the water will flow towards the area where it is the lowest (the hole). Sinking air from a high pressure system will move towards an area of low pressure in an attempt to fill it up. The sinking air will gradually become unstable as it nears the low pressure system, and eventually it will be forced to rise. As the air rises, it will condense at higher altitudes which generates the stormy cumulonimbus clouds, and that is lower level convergence ladies and gentlemen. Now as the air condenses, it will release latent heat, and allow itself to rise even farther in to the atmosphere. When the air reaches the apex altitude, it will finally condense into tiny ice particles (cirrus clouds) and diverge. This is why it always looks like that the white buzz saw shaped clouds always moving away from a Hurricane in satellite imagery, and that is upper level divergence. The diverging air will then converge on top of the high pressure system (it will no condense ort form clouds because it has already lost its moisture) and sink. Subsequently, the sinking air will diverge at the surface and moves towards the area of low pressure, thus repeating the process.

Please note that this is my opinion….if you have any questions, do not hesitate to ask me.

Another reason why I believe it is important to have an adjacent anticyclone nearby is because the sinking air warms adiabatically as it sinks from an anticyclone. That warmer air when flowed toward a cyclone, provide an extra boost. On the contrary, when a trough of low pressure is nearby produces rain, thus cooling the air, which proves to be a burden to the tropical cyclone. So, that is probably one of the reasons why the system in the SW Caribbean is incapable of sustaining itself. However if it does develop, it will likely be in the vicinity of Belize and Honduras.

Central Atlantic

A tropical wave located along 40 degrees west has gotten a bit more organized this afternoon, further development if any will likely be slow to occur over the next couple of days. This system will gradually moves towards the west-northwest over the next couple days. About 120 hours (5 days) from now, it will encounter a trough of low pressure, and might recurve out to sea depending on its intensity, or the potency of the trough. Regardless if this system develops or not, it is best to remain conservative and observe closely for the time being.

***1 I have been noticing thatsome systems actually get better organized during the day, and lose their thunderstorm activity during the night. Thi happened with invest 93L (Kyle), the system in the SW Caribbean, and the weak area of low pressure in the Gulf Of Mexico (GOM) a couple days ago. This kept happening numerous times, and I cannot understand why…..Anyone mind writing a Phd on this one?