My, Paloma!

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Paloma OHC
Mike Moss

I avoided a complete allusion to the Knack by leaving off the "Muh-muh-muh-" I could have put at the beginning of the title, but any way you state it the latter part of last week and the weekend brought a remarkable late season hurricane to the southwestern Caribbean and eventually into the Caymans and Cuba. Thankfully, there have so far been no reported deaths associated with the storm, but it certainly caused significant damage and destruction for parts of the Caymans (especially the more easterly Cayman Brac and Little Cayman) as well as southern parts of eastern Cuba.

This is a storm that lingered for a few days last week as a poorly organized area of low pressure before undertaking a rapid intensification heading into the weekend, one that carried it from initial designation as a minimal hurricane Thursday evening at 7 pm to a category 4 monster with 145 mph maximum sustained winds by 6 am on Saturday. This rapid run-up occurred while the storm was in a location featuring low vertical wind shear (that is, not much difference in speed and/or direction in large scale winds around and across the storm from the lower atmosphere into the upper parts of the storm) and high oceanic heat content (a measure of both the temperature of the ocean water below the storm, and the depth of that warm water). Generally, storms do best with shear values of less than 20 knots or so and significant increases in heat content along their path.

A Paloma page from the University of Wisconsin Cooperative Institute for Mesoscale Meteorological Studies (CIMMS) satellite blog has some very nice animations of Paloma at the peak of its power on Saturday, with both infrared and visible wavelength satellite loops, and also a map of ocean heat content compared to the path of the storm. I've posted a larger copy of that image here. Note that the storm moved north from an area with heat content values of less than 25 to greater than 100 (these are in units of Kilojoules per square centimeter), a very rapid increase in this important energy source.

Also note how rapidly those values fall near Cuba, and you'll see one reason the storm decayed at an even more rapid clip than it had strengthened. Other factors involved in the speedy weakening trend were interaction with the terrain of Cuba and an increase in vertical wind shear associated with the upper level trough that moved into the eastern U.S. over the weekend. That trough helped push a cold front across our area that took us from high temperatures near 80 on Friday down to the mid 60s on Sunday. It also sent vertical wind shear over the storm up to near 40 knots by 7 am Sunday morning, as shown in the second image, a CIMMS depiction of the direction and intensity of deep wind shear. On the map, values in the range of 25 knots or so are shown in yellow (sort of a "caution" color for tropical cyclones, while 40 knots and up is getting into the red zone indicating a very poor environment for these storms). By Sunday morning, this difference in lower and upper level winds had separated the surface circulation center of Paloma from virtually all of it's upper level moisture and deep convection, and left the system to rapidly decay to a very weak remnant low which remains in place today just north of Cuba.



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