Map: Gulf of Mexico Total Precipitable Water September 1-2, 2016
According to Jeff Masters and Bob Henson at Weather Underground:
Near record-warm ocean temperatures in the Gulf of Mexico are evaporating near-record amounts of water vapor into the atmosphere for Hermine to feed off of. At 8 am EDT Wednesday, the upper-air balloon sounding at Tampa, Florida measured 2.5” of total precipitable water (TPW)—the amount of water that would result if one condensed all the water vapor in a column above and precipitated it out. This value ranked in the upper 1% of all TPW measurements taken at the site since 1948.