[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 280223
TCDAT3
TROPICAL STORM LISA DISCUSSION NUMBER  35
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT MON SEP 27 2004

LISA REMAINS IN A SHEARED STATE...BUT THE CYCLONE HAS MANAGED TO
KEEP GENERATING NEW CONVECTION NEAR AND TO THE NORTHEAST OF THE
TIGHT LOW-LEVEL CIRCULATION CENTER. THE INITIAL INTENSITY ESTIMATE
OF 35 KT IS BASED ON NUMEROUS 30-34 KT NON-RAINFLAGGED WIND VECTORS
NOTED IN A 27/2142Z QUIKSCAT OVERPASS. WIND SPEEDS OBVIOUSLY COULD
BE HIGHER IN THE DEEPER CONVECTION IN THE NORTHEAST QUADRANT...BUT
I HAVE OPTED TO KEEP THE INTENSITY A LITTLE LOWER DUE TO THE RAPID
FLUCTUATIONS IN THE CONVECTION IN THAT REGION. THIS LOWER INTENSITY
IS ALSO CONSISTENT WITH THE 1006 MB PRESSURE AND 34 KT WIND
ESTIMATES OBTAINED FROM A 27/2046Z AMSU OVERPASS.

THE INITIAL MOTION ESTIMATE IS 350/07. THE INITIAL POSITION WAS
ADJUSTED SLIGHTLY EASTWARD BASED ON AMSU OVERPASS AND QUIKSCAT
POSITION ESTIMATES. OTHER THAN THAT...THERE IS NO SIGNIFICANT
CHANGE TO THE PREVIOUS FORECAST TRACK REASONING. LISA IS EXPECTED
TO MOVE SLOWLY NORTHWARD BETWEEN A RIDGE TO THE EAST AND A WEAK
TROUGH TO THE WEST. BY 72 HOURS...A SHORTWAVE TROUGH IS FORECAST TO
APPROACH LISA FROM THE WEST AND GRADUALLY RECURVE THE CYCLONE
NORTHEASTWARD. ALL OF THE NHC MODEL GUIDANCE AGREES ON THIS
SCENARIO...AND THE TIMING OF THE NORTHEASTWARD TURN IS THE ONLY
DIFFERENCE BETWEEN THE MODELS. THE OFFICIAL FORECAST TRACK IS
SIMILAR TO THE NHC MODEL CONSENSUS.

LISA IS FORECAST TO REMAIN UNDER SOUTH TO SOUTHWESTERLY VERTICAL
SHEAR FOR THE NEXT 36 HOURS SO LITTLE...IF ANY...SIGNIFICANT
INTENSIFICATION IS EXPECTED DURING THAT TIME. HOWEVER...BY 48-96
HOURS...THE SHEAR IS EXPECTED TO WEAKEN TO LESS THAN 10 KT WHILE
LISA IS STILL OVER 27+ CELSIUS SSTS. THIS SHOULD ALLOW FOR SOME
STRENGTHENING TO OCCUR AND LISA COULD POSSIBLY EVEN REACH MINIMAL
HURRICANE STRENGTH BEFORE INCREASING WESTERLY SHEAR AND COOLER SSTS
INITIATE A WEAKENING TREND BY 120 HOURS.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      28/0300Z 22.3N  46.4W    35 KT
 12HR VT     28/1200Z 23.4N  46.6W    35 KT
 24HR VT     29/0000Z 24.9N  46.9W    35 KT
 36HR VT     29/1200Z 27.0N  47.2W    40 KT
 48HR VT     30/0000Z 29.0N  47.3W    45 KT
 72HR VT     01/0000Z 32.0N  47.8W    55 KT
 96HR VT     02/0000Z 35.5N  47.0W    60 KT
120HR VT     03/0000Z 37.5N  44.5W    55 KT


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