[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 150902
TCDAT1
TROPICAL STORM JEANNE DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT WED SEP 15 2004

SAN JUAN RADAR DEPICTS A TIGHT CIRCULATION AND A WELL-DEFINED OUTER
CURVED BAND IN THE SOUTHEASTERN SEMICIRCLE....AND SATELLITE IMAGERY
INDICATES THE CIRCULATION LIES WELL WITHIN THE MASS OF DEEP
CONVECTION AND ALSO REVEALS THE OUTER CURVED BAND.  DVORAK
INTENSITY ESTIMATES ARE 55 KT FROM BOTH TAFB AND SAB.  OUTFLOW IS
GOOD IN ALL DIRECTIONS EXCEPT THE WEST.  BASED ON THE IMPROVING
SATELLITE AND RADAR PRESENTATION...THE INITIAL INTENSITY IS
INCREASED TO 55 KT.  AIRCRAFT RECONNAISSANCE WILL NOT BE AVAILABLE
FOR JEANNE UNTIL 18Z TODAY.

THE INITIAL MOTION...BASED PRIMARILY ON TRACKING A POORLY-DEFINED
CENTER ON SAN JUAN RADAR...IS ESTIMATED AT 295/7. JEANNE IS
CURRENTLY ON THE SOUTHERN PERIPHERY OF A DEEP LAYER RIDGE...AND
MODEL GUIDANCE AGREES THAT THIS RIDGE SHOULD PERSIST AND MOVE
JEANNE ON A CONTINUED WEST-NORTHWEST MOTION THROUGH ABOUT 48 HOURS.
BEYOND THAT TIME...THE SOLUTIONS DIVERGE...OWING TO DIFFERENCES IN
HOW EACH MODEL HANDLES A WEAKENING IVAN OVER THE SOUTHEASTERN
UNITED STATES AND HOW MUCH RIDGING WILL REMAIN OVER THE EXTREME
WESTERN ATLANTIC. THE GFS HAS NOW MOVED MORE TO THE WEST IN BETTER
AGREEMENT WITH THE REMAINDER OF THE GUIDANCE SUITE...BUT THE GFDL
HAS ALSO MOVED FARTHER LEFT AND IS NOW THE WESTERN OUTLIER. AS A
RESULT...THE CONSENSUS OF THE MODELS HAS NUDGED SLIGHTLY WESTWARD
AT DAYS THREE THROUGH FIVE...AND THE OFFICIAL FORECAST IS ALSO
ADJUSTED JUST SLIGHTLY WEST...AND A BIT FASTER THAN...THE PREVIOUS
ADVISORY.

THE INTENSITY FORECAST IS A CHALLENGE.  THROUGH 36 HOURS...MODEL
GUIDANCE SUGGESTS ENOUGH ANTICYCLONIC FLOW ALOFT TO SUPPORT
INTENSIFICATION...BUT INTERACTION WITH LAND WILL LIKELY LIMIT THE
INTENSIFICATION RATE.  ONCE JEANNE EMERGES NORTH OF THE GREATER
ANTILLES...IT MAY STRUGGLE UNDER STRONGER NORTHERLY SHEAR.
HOWEVER...BOTH THE SHIPS AND GFDL GUIDANCE INSIST JEANNE WILL
SURVIVE THE SHEAR...UNTIL CONDITIONS BECOME MORE FAVORABLE VERY
LATE IN THE FORECAST PERIOD.  THEREFORE...THE OFFICIAL FORECAST
INDICATES SLOW INTENSIFICATION FOR THE FIRST 36 HOURS...LEVELLING
OFF THROUGH 72 HOURS...THEN RESUMING GRADUAL STRENGTHENING ON DAYS
FOUR AND FIVE.

FORECASTER KNABB/AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL      15/0900Z 17.5N  65.1W    55 KT
 12HR VT     15/1800Z 18.1N  66.5W    60 KT...OVER PUERTO RICO
 24HR VT     16/0600Z 19.1N  68.2W    65 KT
 36HR VT     16/1800Z 20.0N  69.9W    65 KT
 48HR VT     17/0600Z 20.8N  71.3W    65 KT
 72HR VT     18/0600Z 22.5N  74.0W    70 KT
 96HR VT     19/0600Z 24.5N  76.0W    75 KT
120HR VT     20/0600Z 27.0N  77.5W    80 KT


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