[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 230304
TCDAT3
TROPICAL STORM LISA DISCUSSION NUMBER  15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT WED SEP 22 2004

METEOSAT-8 IMAGERY DURING THE PAST FEW HOURS INDICATES THAT THE LOW
LEVEL CENTER OF LISA COMPLETELY SEPARATED FROM THE DEEP CONVECTION.
DURING THE PAST FEW HOURS...THE WELL-DEFINED LOW LEVEL CIRCULATION
HAS BEEN DRIFTING...AND IS NOW NEARLY STATIONARY. FURTHER...THIS
LOW LEVEL CENTER TUCKED UNDER CONVECTION ASSOCIATED WITH THE BROAD
CIRCULATION OF THE TROPICAL DISTURBANCE APPROACHING FROM THE EAST.
IN FACT...NEW CONVECTION IS NOW FORMING NEAR THIS LOW LEVEL
CENTER...AND THE CONVECTIVE BANDS ARRIVING FROM THE EAST ALSO SEEM
BE WRAPPING AROUND THE CENTER OF LISA. THEREFORE...THE MERGER OF
THE TWO SYSTEMS APPEARS TO BE IN PROGRESS. WHILE IT IS STILL
POSSIBLE THAT THE MERGED SYSTEM COULD BECOME FOCUSED ELSEWHERE
WITHIN THE BROAD EAST-WEST ORIENTED CIRCULATION...WE WILL FOR NOW
ASSUME THAT THIS WILL NOT OCCUR AND WILL MAINTAIN THE EXISTING LISA
CIRCULATION AS THE DOMINANT ENTITY.

NOW THAT THE DISTURBANCE MOVING IN FROM THE EAST HAS JUST ABOUT COME
INTO PHASE WITH THE CENTER OF LISA...WITH SOME UNCERTAINTY WE
EXPECT A GENERAL WESTWARD MOTION TO BEGIN WITHIN THE NEXT FEW HOURS
AND THEN CONTINUE THROUGH ABOUT 36 HOURS.  NOT SURPRISINGLY...THE
MODELS ARE HANDLING THIS MERGER/INTERACTION IN A VARIETY OF
WAYS AND IT IS DIFFICULT TO FOLLOW A MODEL CONSENSUS...ESPECIALLY
DURING THE FIRST TWO DAYS OF THE FORECAST.  THE MODELS DO GENERALLY
AGREE...HOWEVER...ON AN EVENTUAL TURN TO THE NORTHWEST INTO A
WEAKNESS IN THE NARROW SUBTROPICAL RIDGE TO THE NORTH...FOLLOWED BY
A STRONG UPPER-LEVEL TROUGH OVER THE CENTRAL ATLANTIC THAT SHOULD
INDUCE A NORTH-NORTHWESTWARD MOTION BY DAYS 4
AND 5.  THE OFFICIAL FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY
BEYOND ABOUT 48 HOURS.

LACKING ANY REASON TO CHANGE THE CURRENT INTENSITY...IT WILL BE HELD
AT 45 KNOTS. NORTHERLY SHEAR IS CURRENTLY IMPACTING LISA...BUT
SHIPS INDICATES THIS SHEAR SHOULD ABATE IN ABOUT 36 HOURS...WHICH
MAY ALLOW FOR SOME GRADUAL STRENGTHENING. THE OFFICIAL FORECAST
CLOSELY FOLLOWS SHIPS AND BRINGS LISA TO HURRICANE INTENSITY BY 72
HOURS.

FORECASTER KNABB/AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL      23/0300Z 13.2N  41.2W    45 KT
 12HR VT     23/1200Z 13.2N  41.8W    45 KT
 24HR VT     24/0000Z 13.3N  42.4W    45 KT
 36HR VT     24/1200Z 13.5N  43.2W    50 KT
 48HR VT     25/0000Z 14.0N  44.2W    55 KT
 72HR VT     26/0000Z 16.0N  45.5W    65 KT
 96HR VT     27/0000Z 18.5N  47.0W    70 KT
120HR VT     28/0000Z 21.0N  48.0W    70 KT


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