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Hurricane HERNAN


ZCZC MIATCDEP4 ALL
TTAA00 KNHC DDHHMM
HURRICANE HERNAN DISCUSSION NUMBER  14
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP092008
800 PM PDT SAT AUG 09 2008
 
HERNAN CONTINUES TO SHOW A WELL-DEFINED 20 N MI WIDE EYE IN
SATELLITE IMAGERY.  HOWEVER...THE CLOUD TOPS IN THE EYEWALL HAVE
WARMED AS THE HURRICANE MOVES OVER COOLER SEA SURFACE TEMPERATURES. 
SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB REMAIN 102 KT...
ALTHOUGH THE FINAL DVORAK T-NUMBERS HAVE DECREASED.  BASED ON THESE
DATA...THE INITIAL INTENSITY IS LOWERED TO 100 KT.  THE CIRRUS
OUTFLOW IS GOOD IN THE SOUTHWESTERN SEMICIRCLE AND POOR ELSEWHERE.

THE INITIAL MOTION IS 300/10.  MID-LEVEL RIDGING TO THE NORTHEAST OF
THE HURRICANE IS STEERING IT TOWARD AN UPPER-LEVEL TROUGH SEEN IN
WATER VAPOR IMAGERY NEAR 30N140W.  THE LARGE-SCALE MODELS FORECAST
THIS TROUGH TO WEAKEN AND BE REPLACED BY A WEAK RIDGE DURING THE
NEXT 36-48 HR...WHICH SHOULD RESULT IN HERNAN TURNING MORE
WESTWARD.  ALL TRACK GUIDANCE AGREES WITH THIS SCENARIO...AND THE
NEW FORECAST TRACK FOLLOWS THE MODEL CONSENSUS.  AFTER 72 HR...A
WEAKENING HERNAN SHOULD TURN MORE SOUTHWESTWARD IN THE
NORTHEASTERLY LOW/MID-LEVEL FLOW.  THERE IS SOME SPREAD IN THE
GUIDANCE AT THIS POINT...WITH THE BAM MODELS AND THE NOGAPS CALLING
FOR A MORE WESTERLY MOTION...AND THE UKMET AND ECMWF CALLING FOR A
SOUTHWESTERLY MOTION.  THE FORECAST TRACK IS BETWEEN THESE TWO
EXTREMES AND NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE.

HERNAN SHOULD STEADILY WEAKEN OVER COOLER SSTS DURING AT LEAST THE
NEXT 72 HR....WITH THE SYSTEM BECOMING A TROPICAL STORM IN ABOUT 36
HR.  WHILE THE FORECAST TRACK DOES BRING THE CENTER OVER SLIGHTLY
WARMER...25C...WATER AFTER 72 HR...THE INTENSITY GUIDANCE CONTINUES
TO SHOW A WEAKENING TREND.  THUS...THE INTENSITY FORECAST ALSO
CALLS FOR CONTINUED WEAKENING...BUT NOT A DECAY INTO A
NON-CONVECTIVE REMNANT LOW.  HOWEVER...IF THE CYCLONE MOVES NORTH
OF THE FORECAST TRACK...IT COULD DISSIPATE OVER THE COLD WATER.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      10/0300Z 16.7N 124.9W   100 KT
 12HR VT     10/1200Z 17.2N 126.1W    90 KT
 24HR VT     11/0000Z 17.7N 127.5W    75 KT
 36HR VT     11/1200Z 17.9N 128.8W    60 KT
 48HR VT     12/0000Z 18.0N 130.0W    50 KT
 72HR VT     13/0000Z 17.5N 132.0W    40 KT
 96HR VT     14/0000Z 17.0N 134.0W    30 KT
120HR VT     15/0000Z 16.0N 136.5W    25 KT
 
$$
FORECASTER BEVEN
 
NNNN


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Page last modified: Tuesday, 21-Apr-2009 12:09:38 UTC