Tropical Storm ISAAC

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TROPICAL STORM ISAAC DISCUSSION NUMBER  17
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
500 AM EDT SAT AUG 25 2012
 
THE CIRCULATION OF ISAAC HAS REMAINED RELATIVELY INTACT AFTER MOVING
ACROSS THE SOUTHWESTERN PENINSULA OF HAITI OVERNIGHT. BEFORE THE
CENTER MOVED INLAND...HURRICANE HUNTER AIRCRAFT DATA SUGGESTED THAT
THE CYCLONE HAD PEAK WINDS OF ABOUT 55 KT. ASSUMING THE CYCLONE
WEAKENED A LITTLE AFTER ENCOUNTERING THE HIGH TERRAIN...THE INITIAL
INTENSITY IS LOWERED TO 50 KT FOR THIS ADVISORY.
 
THE INITIAL MOTION ESTIMATE IS 320/12. AS A MID-LEVEL TROUGH LIFTS
OUT OF THE SOUTHEASTERN UNITED STATES...ISAAC WILL MOVE GENERALLY
WEST-NORTHWESTWARD AROUND THE WEST SIDE OF THE SUBTROPICAL RIDGE
FOR THE NEXT THREE DAYS OR SO...AND THEN TURN NORTHWARD LATE IN THE
PERIOD AS A SHORTWAVE TROUGH AMPLIFIES OVER THE EASTERN UNITED
STATES. THERE HAS BEEN LITTLE CHANGE TO THE NHC FORECAST THIS
CYCLE...AND THE NEW TRACK FORECAST IS CLOSE TO THE MIDDLE OF THE
GUIDANCE ENVELOPE AND LIES CLOSE TO THE GFS AND THE TVCA
MULTI-MODEL CONSENSUS THROUGH 96 HOURS. BY DAY 5 THERE IS SOME
DISAGREEMENT AS TO WHETHER ISAAC WILL TURN NORTHEASTWARD AHEAD OF
THE SHORTWAVE TROUGH AS SHOWN BY THE GFS...UKMET...AND THE GFDL OR
BE LEFT BEHIND AS SHOWN BY THE ECMWF AND HWRF. THE NHC DAY 5 POINT
IS BETWEEN THE TWO CAMPS SHOWING A SLOW NORTHWARD MOTION.
 
GIVEN THAT THE CYCLONE HAS FARED RATHER WELL AFTER MOVING ACROSS
HAITI...AND THAT THE TRACK FORECAST HAS ONLY MINIMAL INTERACTION
WITH CUBA...THE INTENSITY FORECAST AFTER 12 HOURS HAS BEEN ADJUSTED
UPWARD FOLLOWING THE TREND OF THE LATEST INTENSITY GUIDANCE. ISAAC
IS EXPECTED TO BECOME A HURRICANE IN ABOUT 36 HOURS...WITH
ADDITIONAL INTENSIFICATION EXPECTED AS THE CYCLONE MOVES INTO THE
EASTERN GULF OF MEXICO IN A FAVORABLE ENVIRONMENT. THE NEW NHC
INTENSITY FORECAST IS CLOSE TO THE INTENSITY CONSENSUS AIDS THROUGH
72 HOURS AND FOLLOWS A BLEND OF THE DECAY SHIPS AND LGEM AFTERWARD.
 
THE NEW NHC FORECAST NECESSITATES THE ISSUANCE OF A HURRICANE
WARNING FOR THE FLORIDA KEYS AND A PORTION OF THE SOUTHWEST COAST
OF FLORIDA AT THIS TIME.
 
IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK OF ISAAC DUE TO THE
UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE
AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT.
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  25/0900Z 19.0N  73.3W   50 KT  60 MPH
 12H  25/1800Z 20.4N  75.0W   50 KT  60 MPH...INLAND
 24H  26/0600Z 22.2N  77.6W   55 KT  65 MPH...OVER WATER
 36H  26/1800Z 23.8N  80.0W   65 KT  75 MPH
 48H  27/0600Z 25.0N  81.8W   70 KT  80 MPH
 72H  28/0600Z 27.7N  84.9W   80 KT  90 MPH
 96H  29/0600Z 30.5N  86.0W   70 KT  80 MPH...INLAND
120H  30/0600Z 32.5N  86.0W   35 KT  40 MPH...INLAND
 
$$
FORECASTER BRENNAN
 
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