Reply #7: Isabel is strengthening... but there is a debate about how much... [View All]

[althecat]

"IF FLIGHT-LEVEL OBSERVATIONS WERE ALL WE HAD...ISABEL WOULD BE A CATEGORY THREE HURRICANE. THE HURRICANE HUNTER AIRCRAFT THIS AFTERNOON FOUND A NUMBER OF SPOTS OF WINDS OF 110-120 KT. THIS WOULD NORMALLY CORRESPOND TO SURFACE WINDS OF 100-105 KT. HOWEVER...NUMEROUS DROPSONDE PROFILES IN THE HIGH WIND REGIONS OF THE CIRCULATION SHOW A CONSISTENT AND UNUSUALLY STEEP FALL-OFF OF WIND IN THE BOUNDARY LAYER. THIS IS CONSISTENT WITH THE MEAGER CONVECTION IN THE HURRICANE CORE. BASED ON THESE PROFILES...THE INITIAL INTENSITY IS SET AT 90 KT. THE UPPER-LEVEL OUTFLOW PATTERN HAS BECOME FAVORABLE...AS WAS FORECAST BY THE GLOBAL MODELS...AND IN FACT THE CIRCULATION ALOFT IS STRENGTHENING. HOWEVER... THERMODYANAMIC FACTORS ARE LIMITING THE ABILITY OF ISABEL TO COMPLETELY RESPOND TO THE FAVORABLE UPPER-LEVEL FORCING. THE OFFICIAL FORECAST DOES NOT ANTICIPATE ANY SIGNIFICANT INCREASE IN STRENGTH PRIOR TO LANDFALL...BUT SHOULD THERE BE A SUBSTANTIAL INCREASE IN DEEP CONVECTION ISABEL COULD QUICKLY REACH CATEGORY THREE STATUS. "

For more including new GFS rainfall forecasts...

http://www.scoop.co.nz/mason/stories/HL0309/S00163.htm