Tropic Watch 10/21/11

By: SouthDadeFish , 4:11 PM GMT on October 21, 2011

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Well it is the last third of October and according to climatology, what you have to look for this time of year are stalled cold fronts over the Western Caribbean that develop a surface low. Well, this is exactly what we see today. A piece of energy has broken off of the cold front that pushed through South Florida two days ago and is sustaining convection over the SW Caribbean. This entity has been declared invest 96L and appears to be trying to tighten up a currently broad surface circulation.



Figure 1.1: 15:45Z Visible image of Invest 96L showing convection with possible spiral bands trying to develop in the northern semicircle of the circulation. I would place the location of the surface center around 12.8N 81.5W.

Wind shear is currently at a relatively favorable 10 knots over the disturbance as shown here:



Also note that shear tendency analysis from CIMSS shows dropping wind shear levels over the past 24 hours, which shows 96L's environment is becoming more conducive for tropical cyclone formation:



850mb vorticity analysis from CIMSS shows vorticity has been increasing over the past 24 hours and is starting to become more concentrated in the SW Caribbean. One thing I think may be helping 96L is forced convergence due to the shape of coastline surrounding 96L. This is a similar situation as to what we see in the Bay of Campeche. 96L has been slowly but steadily organizing over the past few days and if current trends continue I believe recon will find a TD/TS when they fly in tomorrow. It should be noted that every reliable computer model (the dynamic global models such as the GFS, ECMWF, and UKMET) now develop this feature. This is a very good sign for tropical cyclone formation.

Current steering winds are very light, which makes the track forecast complex. It is possible that 96L moves west into Central America and weakens there, however the more reliable computer models are coming into better agreement of a northward drift over the next 3-4 days. I won't speculate on the track of an invest in weak steering currents after this time, but it should be noted that interests in the Western Caribbean, Florida, and the Bahamas should closely monitor the progress of 96L.

Hopefully 96L stays far enough away from Central America that it doesn't dump its heavy rains over the region. I'm afraid this won't be the case.

Also, if you are looking for links and images such as satellite imagery, computer models, etc. to help track Invest 96L and the rest of the tropics I suggest you check out this site for more information.

-Fish

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About SouthDadeFish

I have my B.S. in atmospheric science from Florida International University and am currently in graduate school conducting hurricane research.

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