[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 150230
TCDAT4
HURRICANE IRENE DISCUSSION NUMBER  42
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SUN AUG 14 2005

AN AIR FORCE RESERVE UNIT RECONNAISSANCE AIRCRAFT ON A TEST FLIGHT
MEASURED STRONG ENOUGH WINDS AT 850 MB TO JUSTIFY UPGRADING IRENE
TO A HURRICANE. PEAK FLIGHT LEVEL WINDS WERE 88 KT...WHICH IN FACT
CORRESPONDS TO ABOUT 70 KT AT THE SURFACE...AND THAT IS THE
ASSIGNED ADVISORY INTENSITY. IRENE HAS GOOD OUTFLOW TO THE
NORTHEAST...ALTHOUGH THE WESTERLIES ARE BEGINNING TO IMPINGE ON THE
NORTHWEST QUADRANT. IRENE WILL BE OVER WARM WATERS FOR ANOTHER 24
HOURS OR SO...AND SO SOME ADDITIONAL STRENGTHENING IS POSSIBLE.
GLOBAL MODELS SUGGEST THAT THE SHEAR SHOULD INCREASE SHARPLY AFTER
THAT TIME AS WELL. IRENE IS LIKELY TO BECOME EXTRATROPICAL AND
MERGE WITH A LARGER BAROCLINIC LOW LATE IN THE FORECAST PERIOD.

THE INITIAL MOTION IS 025/10. IRENE HAS ROUNDED THE SUBTROPICAL
RIDGE AND WILL SOON BE DEFLECTED TO THE RIGHT BY THE MID-LATITUDE
WESTERLIES.  THE FLOW IS FAIRLY ZONAL HOWEVER...AND IF IRENE TURNS
SHARPLY TO THE RIGHT IT MAY TAKE A LITTLE WHILE FOR ANY RAPID
ACCELERATION TO OCCUR.  THE OFFICIAL FORECAST SHOWS ONLY A MODEST
ACCELERATION UNTIL A SIGNIFICANT MID-LATITUDE TROUGH APPROACHES IN
ABOUT 72 HOURS.  THERE IS CONSIDERABLE VARIATION IN THE SPEED OF
THE GUIDANCE MODELS...WITH THE GFS BEING THE FASTEST. THE OFFICIAL
FORECAST IS NOT NEARLY THAT FAST...BUT IS FAIRLY CLOSE TO THE
PREVIOUS ADVISORY AND IS NEAR THE FSU SUPERENSEMBLE.

IRENE BECOMES THE SEASON'S THIRD HURRICANE.  THE NORMAL NUMBER OF
HURRICANES FORMED BY THIS DATE IS ONE.  ONLY ONE YEAR...1966...
HAD MORE HURRICANES FORMED BY THIS POINT IN THE SEASON.

FORECASTER FRANKLIN


FORECAST POSITIONS AND MAX WINDS

INITIAL      15/0300Z 35.3N  69.2W    70 KT
 12HR VT     15/1200Z 36.4N  67.8W    75 KT
 24HR VT     16/0000Z 37.6N  65.1W    70 KT
 36HR VT     16/1200Z 38.8N  62.2W    60 KT
 48HR VT     17/0000Z 40.0N  59.0W    55 KT
 72HR VT     18/0000Z 45.0N  51.0W    50 KT...EXTRATROPICAL
 96HR VT     19/0000Z 54.0N  40.0W    40 KT...EXTRATROPICAL
120HR VT     20/0000Z...ABSORBED


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