[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 280832
TCDAT3
TROPICAL STORM LISA DISCUSSION NUMBER  36
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT TUE SEP 28 2004

THE CENTER REMAINS HARD TO LOCATE ON NIGHT-VIS AND INFRARED
IMAGERY...AND SATELLITE FIXES FROM TAFB AND SAB ARE ABOUT 75 MILES
APART.  AMBIGUITIES FROM THE QUIKSCAT PASS AT 2142Z SHOWED THAT THE
CIRCULATION OF LISA WAS ELONGATED ALONG A NNE/SSW AXIS...PERHAPS AS
A RESULT OF THE PERSISTENT ASYMMETRY IN THE DEEP CONVECTION...WHICH
IS CONFINED TO THE NORTHEAST QUADRANT OF THE CYCLONE.  THE
FIRST GOES-12 IMAGES AFTER ECLIPSE ALSO SUGGEST AN ELONGATED
CIRCULATION.  THE INTENSITY FOR THIS ADVISORY WILL BE HELD AT 35
KT...IN BETWEEN THE DVORAK T NUMBERS FROM TAFB AND SAB...AND THE
INITIAL MOTION REMAINS 350/7.

LISA IS MOVING SLOWLY THROUGH A WEAKNESS IN THE SUBTROPICAL
RIDGE...AND THIS IS EXPECTED TO CONTINUE FOR THE NEXT 24 HOURS.
AFTER THAT...MODEL GUIDANCE DIVERGES SOMEWHAT...WITH THE NOGAPS AND
GFDL THE OUTLIERS TO THE WEST AND EAST RESPECTIVELY.  THE GFDL
SEEMS TO WANT TO MAKE LISA FOLLOW THE CONVECTION...AND THE APPARENT
ELONGATION OF THE CIRCULATION MAKES ME THINK THAT THIS COULD BE
STARTING TO OCCUR.  MODEL GUIDANCE HAS BEEN CONSISTENTLY TRENDING
EASTWARD OVER THE PAST FEW FORECAST CYCLES...AND SO I HAVE ADJUSTED
THE OFFICIAL FORECAST EASTWARD OF AND FASTER THAN THE PREVIOUS
ADVISORY.  THE NEW FORECAST IS NEAR A CONSENSUS OF THE
GFS...GFDL...AND UKMET MODELS.

WATER VAPOR IMAGERY SHOWS A WELL-DEFINED UPPER-LEVEL TROUGH
APPROACHING LISA FROM THE NORTHWEST...AND GLOBAL MODEL GUIDANCE
SUGGESTS THAT THIS TROUGH WILL CUT OFF A SHORT DISTANCE WEST OF THE
CYCLONE IN ABOUT 48 HOURS.  IN THE SHORT RUN THIS WILL INCREASE THE
SHEAR OVER LISA...BUT A MORE FAVORABLE UPPER PATTERN FOR
INTENSIFICATION COULD DEVELOP AFTER THE UPPER LOW CUTS OFF AND
MOVES SOUTHWESTWARD.  THIS WOULD BE PARTICULARLY TRUE IF LISA TAKES
THE MORE EASTWARD TRACK FORECAST BY THE GFDL.  LATE IN THE FORECAST
PERIOD LISA IS EXPECTED TO ENCOUNTER COOLER WATERS AND WEAKEN.  THE
OFFICIAL FORECAST IS CLOSE TO THE SHIPS GUIDANCE...BUT CONSIDERABLY
BELOW THAT OF THE GFDL.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL      28/0900Z 23.1N  46.5W    35 KT
 12HR VT     28/1800Z 24.3N  46.6W    35 KT
 24HR VT     29/0600Z 26.3N  46.4W    40 KT
 36HR VT     29/1800Z 28.7N  46.2W    45 KT
 48HR VT     30/0600Z 31.0N  46.0W    55 KT
 72HR VT     01/0600Z 35.0N  45.5W    60 KT
 96HR VT     02/0600Z 38.0N  41.5W    60 KT
120HR VT     03/0600Z 39.0N  36.0W    50 KT


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