Aug 29, 2016

Invest 99L Finally Develops Into Tropical Depression 9 in the Florida Straits

Big Pine Key, FL
USA
by
Jeff Masters
,
Weather Underground
MODIS visible satellite image of Tropical Depression Nine (formerly 99L) forming in the Florida Straits on Sunday afternoon, August 28, 2016. Image: NASA
MODIS visible satellite image of Tropical Depression Nine (formerly 99L) forming in the Florida Straits on Sunday afternoon, August 28, 2016. Image: NASA

After spending ten days in meteorological limbo-land frustrating forecasters as an “Invest”, 99L finally developed into Tropical Depression Nine, confirmed a NOAA hurricane hunter aircraft late Sunday afternoon. But the storm isn’t done perplexing us yet—the model predictions for the future intensity of the storm remain wildly divergent, even if we now have growing confidence that this storm will track into the coast of Florida north of Tampa on Thursday.

Satellite images on Sunday evening showed a steady increase in the intensity and areal coverage of TD 9’s heavy thunderstorms, though Key West radar showed only a few spiral bands trying to form near the center. The depression is not likely to organize quickly, as it was dealing with wind shear that was a moderately high 15 - 20 knots. TD 9 was also struggling with dry air, as seen on water vapor satellite imagery. Sea surface temperatures (SSTs) remained favorable for development, though, near 30 - 30.5°C (86 - 87°F).

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I support a forecast of TD 9 being a strong tropical storm near hurricane strength at landfall—70 mph winds—until the models come into better alignment