[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 270306
TCDAT2
TROPICAL STORM GUSTAV DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL072008
1100 PM EDT TUE AUG 26 2008

BETWEEN 21Z AND 01Z THIS EVENING...RADAR IMAGERY FROM THE CUBAN
RADAR SITE AT GRAN PIEDRA DEPICTED A NICE DOUGHNUT SHAPED MID- TO
UPPER-LEVEL EYE FEATURE ALONG THE NORTH COAST OF THE SOUTHWESTERN
PENINSULA OF HAITI. HOWEVER...SINCE THAT TIME BOTH RADAR AND
SATELLITE DATA INDICATE THE EYE FEATURE HAS DEGENERATED INTO A
RAGGED AND POORLY DEFINED FEATURE. THEREFORE...GUSTAV HAS BEEN
DOWNGRADED TO A TROPICAL STORM AND THE INTENSITY LOWERED TO 60
KT...WHICH IS ONLY SLIGHTLY BELOW THE T4.0/65 KT SATELLITE
INTENSITY ESTIMATES DERIVED AT 00Z. UPPER-LEVEL OUTFLOW IS SLIGHTLY
RESTRICTED BUT IMPROVING IN THE NORTHWESTERN QUADRANT... AND IS
EXCELLENT IN THE OTHER THREE QUADRANTS.

THE AVERAGE MOTION OVER THE PAST 6 HOURS IS 290/07...ALTHOUGH THE
MOTION OVER THE PAST 3 HOURS HAS BEEN ALMOST DUE WEST. THE PRIMARY
STEERING MECHANISM FOR THE NEXT 5 DAYS WILL BE THE LARGE MID- TO
UPPER-LEVEL ANTICYCLONE CENTERED OVER THE FLORIDA STRAITS...WHICH
IS FORECAST TO AMPLIFY NORTHWARD OVER THE SOUTHEASTERN U.S. AND AN
UPPER-LEVEL TROUGH OVER THE NORTHWESTERN GULF IS ALSO EXPECTED TO
BE A PLAYER AND ACT TO SLOW DOWN GUSTAV BY DAY 5. THE EXCEPTIONS
ARE THE GFDL AND ECMWF MODELS...WHICH BLAST GUSTAV NORTHWESTWARD
THROUGH THE UPPER-TROUGH TO THE TEXAS COAST.  THIS SEEMS PHYSICALLY
UNLIKELY AT THIS JUNCTURE. THE OFFICIAL FORECAST CALLS FOR GUSTAV
TO GRADUALLY MOVE AROUND THE SOUTHERN PERIPHERY OF THE MID-LEVEL
RIDGE TO THE NORTH AND MOVE OUT INTO THE CENTRAL GULF OF MEXICO BY
DAYS 4 AND 5. THE OFFICIAL FORECAST TRACK IS CLOSE TO THE PREVIOUOS
ADVISORY TRACK...AND REMAINS ON THE RIGHT SIDE OF THE GUIDANCE
ENVELOPE IN THE EXPECTATION THAT THE SOUTHWESTERLIES ASSOCIATED
WITH THE UPPER TROUGH WILL PLAY A MORE PROMINENT ROLE THAN
INDICATED BY THE GFDL AND ECMWF.

GUSTAV IS ON THE EAST SIDE OF A LARGE UPPER-LEVEL ANTICYCLONE...
WHICH IS INDUCING SOME LIGHT NORTHERLY SHEAR ON THE CYCLONE.
HOWEVER...THE FLOW IS ALSO STRONGLY DIFLUENT...WHICH SHOULD AID THE
RE-INTENSIFICATION PROCESS ONCE GUSTAV CLEARS THE WESTERN PORTION
OF HAITI. BOTH THE UPPER-LEVEL FLOW AND OCEANIC CONDITIONS OVER THE
NORTHWESTERN CARIBBEAN BETWEEN 36 AND 72 HOURS ARE EXPECTED TO BE
CONDUCIVE FOR SIGNIFICANT INTENSIFICATION TO OCCUR...AND THIS IS
REFLECTED IN THE OFFICIAL FORECAST BY BRINGING GUSTAV TO JUST BELOW
CATEGORY 4 STRENGTH BY 72 HOURS. AFTER THAT...POSSIBLE EYEWALL
REPLACEMENT CYCLES AND SOUTHWESTERLY WIND SHEAR MAY CREATE
INTENSITY FLUCTUATIONS IN THE LATTER FORECAST PERIODS.

FORECAST POSITIONS AND MAX WINDS

INITIAL      27/0300Z 18.6N  73.6W    60 KT
 12HR VT     27/1200Z 18.9N  74.5W    65 KT
 24HR VT     28/0000Z 19.0N  75.7W    75 KT
 36HR VT     28/1200Z 19.2N  77.1W    85 KT
 48HR VT     29/0000Z 19.4N  78.5W    95 KT
 72HR VT     30/0000Z 20.5N  82.2W   110 KT
 96HR VT     31/0000Z 23.0N  86.0W   110 KT
120HR VT     01/0000Z 26.5N  89.5W   110 KT

$$
FORECASTER STEWART/FRANKLIN



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