5/31/2005 Florida Everglades Supercell

Hello, everyone!

I was out in the Plains May 15-27 where I struck out - including the May 21 Convective Inhibition box in eastern Nebraska. :) However, I somewhat made up for that this afternoon when the mesoscale aspects of South Florida weather delivered a supercell over the Everglades.

If you look at the Miami sounding this evening, you might be wondering how a supercell developed. While the CAPE of 1573 is reasonable (and the actual CAPE near the storm may have been somewhat higer), there are no winds greater than 15 kt below 600 mb. Also, the mean storm motion would produce a rather low storm-relative helicity value. These conditions aren't that unusual here this time of year.

However, during South Florida summers we get a lot of boundary collisions - colliding sea breezes, sea breezes colliding with lake breezes, and those boundaries colliding with various outflow boundaries.
Sometimes when this happens (and it's hard to predict when it will), the resulting thunderstorm has a very deviant motion - which with a wind profile like today's can cause it to rotate. The storm I saw today moved slowly southward against the mean flow, which was in sharp contrast to other nearby storms.

The storm began to develop at roughly 5 PM and I intercepted it at Shark Valley along US 41 at about 6 PM. At that time, it had a classic supercell appearance with a tilted updraft, good base, a ragged wall cloud, low and mid-level inflow bands, inflow surface wind, a vault, and good visual rotation. I watched it for about an hour-and-a-half, during which time it went through cycles of organization and disorganization. No tornado genesis occurred (I guess that needed a few more knots on the low level winds), but three times there were scud tags trying to become funnels. The storm started to die about 8 PM and dissipated by 9 PM.

The WFO Miami issued a Severe Thuderstorm Warning on this storm based on strong rotation seen in 88D winds. I can't verify that the winds reached severe criteria, as the RFD part of the storm was inaccessable.
I didn't encounter any hail, which given my position just east of the vault may have been just as well. :) (If this had been a typical Oklahoma or Kansas storm I'd probably be looking for a new car right now.) There was a tremendous amount of CG lightning even by Florida standards - so much that I didn't want to get out of the car.

All things considered, this was a pretty good chase or intercept. The one sour note is that I didn't have a camera. :(

Jack Beven
 
Nice Jack,

The weather you describe is very, very similar to what I have here in sern China, with the difference that we get even more contrasts sometimes due to extreme low level moisture (dews nearly 80F).

However, here storms are turning more "tropical" now with the upper level jet reverting from west to east. Anyway, easterly storms are also not bad here, especially when the easterly jet meet a strong sfc boundary of dry and very hot air from the north (it happens when a low pressure pass in the South China Sea, quite often during summer). In this case we can have very severe straight line winds and hail, with CAPE often exceeding 6-7.000.

:wink:
 
Found the sounding that preceed the storms by 4 hours:

17402.gif


:wink:
 
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