First Subtropical Blob of the Season

While I was watching the deep tropics in the long range models, an area of low pressure developed this afternoon into a sheared dry subtropical low pressure system. This system is located just north of Puerto Rico and east of the Turks and Caicos islands. It seems as though this will likely be dead within the next 24 hours due to shear.

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Synoptically, this isn’t the most beautiful system to look at, but for the month of May, this is what should be expected. The system is mainly in the mid levels, however it does have a surface reflection with a sea level pressure of 1014 mb. The low level cyclone seems to be pulling away to the west. It is a closed system, however it’s core temperature is relatively the same as the environment around it, which is what makes it a subtropical system. The sea surface temperatures which would assist in warming the core are slightly less than marginally favorable. The system is shrouded in an area of very dry air, which is centered over the Bahamas. In the upper levels, winds are out of the west at 10-20 knots, which is semi-favorable for development. The system has a rather robust eastern (downshear) side, but it’s core has only had intermittent thunderstorm activity.

Shear 24 hours from 2pm 5/11


The forecast above calls for deep layer shear to increase into the very unfavorable category, which also continues for the future. I also believe that the upper level support which allowed for any development in the first place will be gone within 12 hours or so. Dry air will make its intrusion into the core with help from the increasing shear by mid to late afternoon tomorrow. I do believe, that if the diabatic effects are strong overnight that an invest may be declared by the National Hurricane Center for modeling purposes. The chances of this are rather low since the NHC likes to declare interest areas that will last for a while, kinda like your interest in buying a car that will last 40 mpg rather than a car that will only last 20 mpg. The analogy  will stand throughout the season.

Climatologically, as I posted earlier in the week, this isn’t quite in the area one would expect for pre-season storms. That’s not to say that storms cannot form there.

What’s next?

The long range (La La Land range) models are persistent with a feature in the southern Caribbean in about 8-11 days. So far, the GFS has had the same system for 8 consecutive runs, and weaker reflections of the same system are shown on the GEM and Euro. The GEFS also shows this with expected considerable spread. The exact timing has been sliding backward. Generally this slide means that the system will never form, however with a strong MJO pulse expected in the same region this will have to be watch. Right now, this has a near 0% chance of happening, but keep watching here for the latest.

As always, you can follow me on twitter @JonathanBelles for intermediate comments. Good things are coming!


Posted on Saturday, May 11th, 2013, in Tropical Weather. Bookmark the permalink. Leave a comment.

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