[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 012033
TCDAT2

TROPICAL STORM PHILIPPE DISCUSSION NUMBER  31
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL172011
500 PM AST SAT OCT 01 2011

AN ASCAT SWATH PARTIALLY CAUGHT PHILIPPE AT 1331 UTC...AND SOMEWHAT
SURPRISINGLY...IT SHOWED A COUPLE OF 55-KT WIND BARBS LOCATED TO
THE NORTH OF THE CENTER.  THIS IS BEING SET AS THE INITIAL
INTENSITY...AND IT COULD BE CONSERVATIVE DUE TO A POTENTIAL LOW
BIAS IN THE DATA...AND BECAUSE THE ENTIRE WIND FIELD WAS NOT
MEASURED BY THE INSTRUMENT.  GIVEN THE HIGHER INITIAL INTENSITY...
THE NEW OFFICIAL FORECAST HAS BEEN INCREASED THROUGHOUT THE
FORECAST PERIOD BUT INDICATES THE SAME GENERAL PATTERN OF WEAKENING
AND RE-STRENGTHENING AS BEFORE.  THE REASONING FOR THIS INTENSITY
FORECAST HAS NOT CHANGED.  STRONG NORTHERLY SHEAR IS EXPECTED TO
IMPACT PHILIPPE FOR THE NEXT 3 DAYS OR SO AND SHOULD INDUCE SOME
GRADUAL WEAKENING.  THE SHEAR COULD RELAX BY DAY 4 WHEN PHILIPPE
REACHES A NARROW UPPER-LEVEL RIDGE AXIS...AND THE STATISTICAL
MODELS...AS WELL AS THE GFDL...ARE SUGGESTING THAT SOME
STRENGTHENING COULD OCCUR.

THE INITIAL MOTION REMAINS 300 DEGREES AT 8 KT.  A LOW- TO MID-LEVEL
AREA OF HIGH PRESSURE OVER THE SUBTROPICAL CENTRAL ATLANTIC IS
FORECAST TO BUILD SOUTHWESTWARD IN THE WAKE OF HURRICANE OPHELIA...
AND THAT SHOULD TURN PHILIPPE WESTWARD OVER THE NEXT 24 TO 48
HOURS.  THE GLOBAL MODELS AGREE THAT A WEAKNESS WILL DEVELOP IN THE
RIDGE BY DAY 3 WITH PHILIPPE RESPONDING BY SLOWING DOWN AND TURNING
TOWARD THE NORTH.  THERE CONTINUES TO BE DISAGREEMENT AMONG THE
MODELS ABOUT WHETHER OR NOT PHILIPPE WILL BE PICKED UP BY THE FLOW
AHEAD OF A LARGE CUT-OFF LOW NEAR THE NEW ENGLAND COAST.  THE GFS
IS STILL A SLOWER AND SOUTHERN OUTLIER...HAVING PHILIPPE MISS THE
TROUGH AND GETTING STUCK TO THE SOUTH OF A POST-FRONTAL HIGH
PRESSURE SYSTEM.  DUE TO THE LARGE SPREAD IN THE GUIDANCE...THE
OFFICIAL FORECAST IS STILL SLOWER THAN THE MODEL CONSENSUS ON DAYS
4 AND 5.

BASED ON THE ASCAT DATA...ADJUSTMENTS TO THE WIND RADII AND THE
12-FT SEAS RADII WERE REQUIRED ON THIS FORECAST ADVISORY.

FORECAST POSITIONS AND MAX WINDS

INIT  01/2100Z 25.2N  49.1W   55 KT  65 MPH
 12H  02/0600Z 25.6N  50.6W   55 KT  65 MPH
 24H  02/1800Z 25.9N  52.6W   50 KT  60 MPH
 36H  03/0600Z 25.8N  54.9W   45 KT  50 MPH
 48H  03/1800Z 25.7N  57.1W   40 KT  45 MPH
 72H  04/1800Z 26.5N  61.0W   40 KT  45 MPH
 96H  05/1800Z 28.5N  61.0W   45 KT  50 MPH
120H  06/1800Z 32.0N  57.0W   50 KT  60 MPH

$$
FORECASTER BERG



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