https://phys.org/news/2018-09-nasa-noaa-satellite-tropical-depression-isaac.html

On Sept. 14 at 1:36 a.m. EDT (0536 UTC) the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard NASA-NOAA's Suomi NPP satellite captured an infrared image of Tropical Depression Isaac in the eastern Caribbean Sea. VIIRS showed wind shear was tearing the storm apart. The coldest cloud top temperatures of strongest thunderstorms were as cold as minus 70 degrees Fahrenheit/minus 56.6 degrees Celsius and were limited to one area of the storm.

The National Hurricane Center or NHC said "Although the system is still producing areas of deep convection, [satellite imagery] indicated that the circulation had become even less defined.