23 September 2010

Lisa downgraded to TD, disturbance in southern Caribbean getting better organized...

Lisa has been plagued by a hostile environment with moderately strong vertical shear and moderately dry low-mid level air... a bad combination if you're a tropical cyclone.  As a result the storm was downgraded to a Depression at 09Z today, and remains so at 15Z.  However, there is a 1-2 day window of opportunity beginning now where the environment should improve before drier air invades again.  Regardless, Lisa will remain a weak storm and far from any land.

On the other hand, that area of disturbed weather that was skimming the Venezuelan coast the past couple of days is now located north of western Columbia and heading west toward Nicaragua.  The environment in which this system is embedded couldn't be any more conducive for significant development: 30C SSTs, 5 kts of vertical shear, and huge values of ocean heat content.  Though it has taken nearly a week to get spun up (not out of the norm), it appears that it is now nearly a Depression and could quickly intensify to TS Matthew.  As I mentioned before, a system like this must be watched very closely, because it WILL affect land, and probably have 1-3 landfalls in its lifetime.  I've been perusing the global model output regularly, and an overall trend and consensus is to bring the storm gradually WNW through much of the western Caribbean, then perhaps a NW turn to bring it up into the Yucatan Straights area by the middle of next week.
A recon plane left St. Croix early today and is conducting multiple penetrations through the system as I type this.  So far, a central pressure of 1008mb has been found, along with 36kt flight-level winds (corresponds to nearly tropical storm force at the surface).

Please visit my tropical Atlantic headquarters.

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