Friday, October 23, 2015

Major Flood Threat This Weekend

Nearly two-thirds of the state of Texas along with almost the lower half of Louisiana could see some astonishing rainfall this weekend. The green-shaded areas depicted above are under flash flood watches. 

It is possible that over a foot of rain could fall, bringing dangerous conditions to locations that have been very dry for weeks. Remnants of record-setting hurricane Patricia will combine with a cold front progressing across the central Plains, setting the stage for widespread misery.

When I first saw the blaring headlines that the Pacific hurricane named Patricia was the "strongest on record", I thought it was more media hyperbole. However, this time, it's fact. The two main measures of hurricane potency are maximum winds and central pressure. The lower the pressure, the stronger the storm. Here's what it looked like. when it made landfall Friday evening:

This is different than impact, because a storm could strengthen over warm water, far from harming anyone. However, when that danger looms, it certainly gets our attention.

Here's an idea of how strong Patricia is compared to its predecessors:

STORM         YEAR        MAX WINDS  (mph)       CENTRAL PRESSURE (mb)
Patricia        2015               200                              879
Wilma          2005               185                              882
Gilbert        1988                185                              888
Labor Day    1935                185                             892
Rita             2005                180                             895
Allen           1980                190                             899

The storm will weaken with regard to those two parameters as it encounters the mountains of central Mexico, but the moisture from the storm will be drawn into southern and central Texas by Saturday. Here's what computer models show for Saturday afternoon:

By late Sunday, here's the projection for accumulated rainfall. The purple shading indicates amounts that could easily exceed one foot:

Residents in the watch areas should stay alert to rapidly changing conditions as rain will fall repeatedly over the same areas, leading to the flash flood threat. Remember the live-saving adage - turn around, don't drown. The majority of the fatalities from the catastrophic South Carolina flooding earlier this month occurred in cars. People either got trapped in rapidly rising water or they ignored "road closed" signs and drove around barricades.

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