Invest area 99L forms in tropical Atlantic as conditions become more favorable

The NHC is monitoring an area of low pressure well to the south and west of the Cape Verde Islands for possible development. It appears that conditions across the region are becoming more conducive for tropical cyclone formation. The dry, dusty air seen in recent weeks has significantly decreased and water temps are just warm enough to support development.

Vertical wind shear in the tropical Atlantic

Vertical wind shear in the tropical Atlantic

Looking at some of the parameters typically associated with tropical cyclone formation, we see that vertical wind shear, the difference in wind speed and direction with height in the atmosphere, is right where it should be for this time of year. In other words, shear is not a factor. It is running at about the climatological average. This should allow for a steady growth in deep tropical thunderstorms or convection. In turn, this will allow the pressures to continue to fall as the fairly large envelope of energy gradually consolidates as it moves westward.

Vertical instability in the tropical Atlantic

Vertical instability in the tropical Atlantic

On the other hand, vertical instability, which is more or less a way of saying how stable is the atmosphere. Yet another way to put it is how difficult is it to lift the air and get the vertical motion needed to create tropical convection? Right now, vertical instability is running quite a bit below the average for the tropical Atlantic. This means that we will not see rapid development of 99L. However, this is not necessarily good news. The reason? Typically, the sooner a system develops, the more chance it has to be picked up by a weakness in the subtropical ridge and track out to sea. The later the development takes place, the farther west we usually see storms and hurricanes track. So even though vertical instability is running below normal right now, it likely only means a delay in development and should not be enough to limit it completely.

Looking at the global computer models, the GFS seems to be the most consistent with development and an eventual track through the Windward Islands. The ECMWF has basically no development from this system while the Canadian CMC model seems a little too aggressive and thus has a more northerly track over the next five to six days. It during these early stages of what is called cyclogenesis that the models will waver and not be of much use. The good news is that 99L is way out in the tropical Atlantic and we will have several days to monitor its progress.

I do think that it is a good reminder that we are entering the busy months of the hurricane season. Whether or not 99L develops, August is fast approaching and the need to be ready for what the next 90 days or so brings is critical. For the next few days, folks in the Lesser Antilles should be watching 99L closely. It has a chance to develop and at least bring inclement weather to the region. How much it develops remains to be seen. It is very early in the process and much will change over the week ahead. I’ll post regular updates here and on our Facebook and Twitter pages. Keep in mind that beginning Wednesday, August 1, you will be able to purchase our brand new HurricaneTrack app for iPhone/iPod Touch (it will work on an iPad though it is not formatted for that device per se). The app will feature an in-depth daily video blog that will keep you informed through the use of graphics and narration concerning any goings on in the tropics. I’ll have a special link and blog post on Wednesday once the app is available.

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