[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 270854
TCDAT3
TROPICAL STORM LISA DISCUSSION NUMBER  32
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT MON SEP 27 2004

LISA HAS REMAINED STEADY-STATE OVERNIGHT WITH LITTLE CHANGE IN THE
SHEARED CONVECTIVE PATTERN...WITH NO NET CHANGE IN THE DEPTH OF THE
CONVECTION WHICH HAS BEEN PULSATING NORTHEAST OF THE CENTER.  THE
INITIAL INTENSITY OF 45 KT IS UNCHANGED FROM THE PREVIOUS ADVISORY
AND IS BASED ON DVORAK CI NUMBERS OF 3.0 FROM TAFB...SAB...AND AFWA.

SHORTWAVE IR IMAGERY FROM GOES-12 AND METEOSAT-8 INDICATE A
CONTINUED SLOW MOTION...ESTIMATED TO BE JUST WEST OF DUE NORTH AT
ABOUT 5 KT.  LISA IS EMBEDDED WITHIN WEAK STEERING CURRENTS IN
BETWEEN RIDGING TO THE EAST AND WEST.  MOST OF THE DYNAMICAL
MODELS...WITH THE EXCEPTION BEING THE UKMET...INSIST THAT A TURN
TOWARD THE NORTH-NORTHWEST WILL BEGIN VERY SOON AS THE EASTERN
RIDGE BUILDS SLIGHTLY TO THE NORTH AND NORTHEAST OF LISA.  THE
OFFICIAL FORECAST FOLLOWS A CONSENSUS OF THE DYNAMICAL MODELS
THROUGH ABOUT 48 HOURS.  THE MODELS DIVERGE SIGNIFICANTLY AT DAYS
THREE THROUGH FIVE...WITH THE NOGAPS AND GFDL SHOWING A SLOW
NORTHWESTWARD MOTION...AND THE GFS AND UKMET DEPICTING RECURVATURE
FOLLOWED BY RAPID MOTION TO THE NORTHEAST.  THE UKMET SEEMS A BIT
FAST INITIALLY...AND THE GFS TRACK RESULTS FROM THE MODEL FORMING A
NEW VORTEX WELL TO THE NORTHEAST OF THE CURRENT ONE...SO WE ARE NOT
QUITE READY TO FOLLOW THESE SOLUTIONS.  THE OFFICIAL FORECAST IS
ADJUSTED SLIGHTLY TO THE EAST THROUGH 72 HOURS...AND THEREAFTER IS
VERY SIMILAR TO THE PREVIOUS ADVISORY.  THE UNCERTAINTY IN THIS
FORECAST REMAINS LARGE.

UNTIL THE CURRENT SOUTHWESTERLY SHEAR RELAXES IN 36 TO 48 HOURS...AS
FORECAST BY THE GFS/SHIPS...THE INTENSITY SHOULD REMAIN FAIRLY
STEADY.  THEREAFTER...WITH WEAKER SHEAR AND SSTS STILL GREATER THAN
27 DEGREES CELSIUS...BOTH SHIPS AND GFDL FORECAST SHOW
INTENSIFICATION TO HURRICANE STRENGTH BY 72 HOURS.  THE OFFICIAL
FORECAST FOLLOWS THIS SCENARIO.

FORECASTER KNABB/FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL      27/0900Z 20.2N  46.2W    45 KT
 12HR VT     27/1800Z 21.4N  46.5W    45 KT
 24HR VT     28/0600Z 22.8N  47.3W    45 KT
 36HR VT     28/1800Z 24.2N  48.1W    50 KT
 48HR VT     29/0600Z 25.6N  48.9W    55 KT
 72HR VT     30/0600Z 28.0N  50.1W    65 KT
 96HR VT     01/0600Z 30.0N  51.0W    65 KT
120HR VT     02/0600Z 31.5N  51.5W    65 KT


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