Forecast Insight – T.S. Isaac

Forecast Hydromet Insight

• T.S. Isaac seems to be showing some sign of organization as of mid-morning.  There are increasing signs of enhanced upper outflow and convection.  Still, overall, the system is weak and generally unorganized. 
• The movement of Isaac, as of 11 a.m., was west-northwest.  This is significant.  Models have been strongly predicting a turn to the northwest.  This – might – be the start of this northwest turn.  Once Isaac turns northwest, there will be an increased confidence in the forecast.
• Isaac will move over land (Cuba) over the next day or so.  Increases in strength and organization will likely be slow until it moves back over the Gulf of Mexico.
• The rainfall gradient will be extremely tight over Florida.  Heavy rain is likely over South Florida as Issac will near the coastline.  As it pulls away from the central Florida coast, there will be a very tight gradient from 8 inches of rain (or more) to only a couple of inches of rain.  Where this rainfall gradient establishes will determine the eventual threat for river flooding.
• Central Florida rivers are already running very high.  Any rain above 2 or 3 inches would cause more widespread and significant flooding.
• Impacts from Isaac will likely continue through much of next week – and well inland.  The most likely path for Issac will be a landfall near Pensacola before being picked up and lifted northeast.  While some parts of the Southeast U.S. can handle 3 to 4 inches (or more) of rain – other spots, including Mississippi, Alabama, and the Carolinas have received more rainfall.  We need to keep alert for inland flooding over portions of the Southeast U.S. next week as there is a very large degree of uncertainty once (or if) Isaac moves inland.