[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 202100
TCDAT3
TROPICAL STORM LISA DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT MON SEP 20 2004

ALTHOUGH BANDING FEATURES HAVE CONTINUED TO IMPROVE...LISA STILL
REMAINS A SMALL TROPICAL CYCLONE. THE BANDING EYE FEATURE OBSERVED
EARLIER TODAY HAS DISSAPEARED UNDER A STRONG BURST OF DEEP
CONVECTION OVER THE CENTER. THE INCREASED CONVECTIVE STRUCTURE...
THE INCREASE IN THE CENTRAL DEEP CONVECTION...AND A 20/1547Z AQUA1
OVERPASS SHOWING A MID- AND LOW-LEVEL EYE FEATURE ARE MY REASONS
FOR REMAINING HIGHER THAN THE DVORAK SATELLITE INTENSITY ESTIMATES
OF 45 KT FROM BOTH TAFB AND SAB...AND 35 KT FROM AFWA.

THE INITIAL MOTION ESTIMATE IS 280/10.  THERE REMAINS NO
SIGNIFICANT CHANGE TO THE PREVIOUS TRACK FORECAST OR REASONING.
LISA IS EXPECTED TO CONTINUE MOVING IN A WEST TO WEST-NORTHWESTWARD
DIRECTION THROUGHOUT THE FORECAST PERIOD AS THE SMALL CYCLONE MOVES
AROUND THE PERIPHERY OF A NARROW SUBTROPICAL RIDGE LOCATED BETWEEN
LISA AND KARL. THE RIDGE IS FORECAST BY MOST OF THE MODELS TO
REMAIN INTACT...DESPITE THE POOR INITIALIZATION OF THE CYCLONE BY
ALL OF THE MODELS EXCEPT FOR NOGAPS. HOWEVER...THE NOGAPS MODEL
APPEARS TO OVERDEVELOPMENT OF THE CYCLONE...WHICH ALLOWS IT TO
ERODE THE NARROW RIDGE AND MOVE NORTHWESTWARD THROUGH IT. ON THE
OTHER HAND...THE GFDL...GFDN...AND DEEP BAM MODELS MOVE LISA
WESTWARD FOR ABOUT 72 HOURS AND THEN SOUTHWESTWARD AS A RIDGE
DEVELOPS TO THE NORTHWEST. UNTIL THE MODELS COME INTO MORE
REASONABLE AGREEMENT...THE OFFICIAL FORECAST REMAINS CLOSE TO THE
PREVIOUS FORECAST TRACKS AND FOLLOWS THE SYNOPTIC PATTERN OF ENOUGH
RIDGING KEEPING THE VERY SMALL TROPICAL CYCLONE MOVING WESTWARD...
WITH A GRADUAL DECREASE IN FORWARD SPEED AS THE RIDGE WEAKENS SOME.

COMPACT TROPICAL CYCLONES LIKE CAN STRENGTHEN FAIRLY QUICKLY...BUT
CAN ALSO WEAKEN JUST AS FAST. THE VERTICAL SHEAR IS FORECAST TO
REMAIN AROUND 10 KT OR LESS FOR THE NEXT 12 TO 18 HOURS...WHICH MAY
ALLOW LISA TO STRENGTHEN INTO A HURRICANE LATER TONIGHT OR TUESDAY.
AFTERWARDS 36 HOURS...LOW TO MODERATE NORTHEAST TO EASTERLY
VERTICAL SHEAR IS EXPECTED TO INHIBIT THE INTENSIFICATION
INTENSIFICATION PROCESS...BUT NOT AS MUCH AS IF IT WAS WESTERLY
SHEAR. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS
INTENSITY FORECAST...WHICH IS CONSISTENT WITH THE SHIPS MODEL...BUT
MUCH HIGHER THAN THE GFDL MODEL.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      20/2100Z 13.8N  36.8W    55 KT
 12HR VT     21/0600Z 14.1N  38.2W    65 KT
 24HR VT     21/1800Z 14.6N  39.9W    70 KT
 36HR VT     22/0600Z 15.2N  41.6W    75 KT
 48HR VT     22/1800Z 15.9N  43.2W    75 KT
 72HR VT     23/1800Z 16.7N  46.0W    80 KT
 96HR VT     24/1800Z 17.0N  49.0W    75 KT
120HR VT     25/1800Z 17.0N  52.0W    75 KT


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