[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 270259
TCDAT3
TROPICAL STORM LISA DISCUSSION NUMBER  31
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SUN SEP 26 2004

LISA CONTINUES TO PRODUCE SPORADIC BURSTS OF DEEP CONVECTION ON THE
NORTHEAST SIDE OF AN OCCASIONALLY-EXPOSED LOW-LEVEL CENTER.  A 2337
UTC SSMI MICROWAVE PASS SHOWED THAT THE CYCLONE IS A LITTLE FARTHER
SOUTH THAN THOUGHT AND HAS BEEN MOVING RATHER SLOWLY.  DVORAK
INTENSITY ESTIMATES HAVE NOT CHANGED WITH A SHEARED TROPICAL
CYCLONE PATTERN PRESENT SO THE INITIAL INTENSITY REMAINS 45 KT.

MICROWAVE FIXES INDICATE THE STORM HAS BEEN MOVING GENERALLY TO THE
NORTH AROUND 5 KT FOR THE PAST 6-12 HOURS. THE OFFICIAL FORECAST IS
SHIFTED A LITTLE TO THE RIGHT IN THE NEAR-TERM TO ACCOUNT FOR THE
SLOWER AND MORE NORTHERLY MOTION.A MORE NORTHWESTERLY OR
NORTH-NORTHWESTERLY MOTION SHOULD COMMENCE SOON DUE TO A MIDDLE-
LEVEL RIDGE BUILDING TO THE NORTH AND NORTHEAST OF LISA. THE
FORECAST BEYOND 2 DAYS IS RATHER UNCERTAIN WITH CONSIDERABLE SPREAD
IN MODEL GUIDANCE. THERE SEEMS TO BE TWO CLUSTERS OF SOLUTIONS
EMERGING. THE UKMET/GFS MODELS WANT TO RECURVE LISA THRU A BREAK IN
THE SUBTROPICAL RIDGE ALONG 50W. THE OTHER CLUSTER COMPOSED OF THE
NOGAPS/GFDN/GFDL SUGGESTS THAT THE STORM WILL NOT RECURVE AND WILL
INSTEAD TAKE A WESTERLY TURN UNDER A BUILDING RIDGE OVER THE
WEST-CENTRAL ATLANTIC. IF THE CURRENT SLOW MOTION CONTINUES THE
MORE WESTERLY MOTION COULD BE CORRECT AS THE RIDGE WOULD HAVE MORE
TIME TO BUILD TO THE NORTH OF LISA. WITH SO MUCH UNCERTAINTY...THE
OFFICIAL FORECAST WILL SLOW THE MOTION CONSIDERABLY IN THE MEDIUM-
RANGE BETWEEN THE TWO CLUSTERS.

IN ADDITION TO ABOUT 15-20 KT OF SOUTHWESTERLY SHEAR...LISA HAS BEEN
MOVING OVER THE COOL WAKE OF KARL...FURTHER HINDERING ITS
DEVELOPMENT. LITTLE CHANGE IN STRENGTH IS LIKELY UNTIL AFTER 24
HOURS WHEN THE STORM MOVES OVER WARMER WATER WITH ABOUT THE SAME
AMOUNT OF SHEAR. GLOBAL MODEL GUIDANCE SUGGESTS THAT THE SHEAR WILL
DECREASE IN TWO OR THREE DAYS AS AN UPPER TROUGH CUTS OFF FROM THE
MID-LATITUDES WEST OF LISA. THIS PATTERN WOULD BE SLIGHTLY MORE
FAVORABLE FOR INTENSIFICATION OVER WARM WATER NEAR 28C BUT THERE IS
CONSIDERABLY UNCERTAINTY ON WHERE THE STORM WILL BE AT THAT POINT.
WITH SO MUCH AMBUIGUITY PRESENT THERE IS NO CHANGE TO THE PREVIOUS
INTENSITY FORECAST.

FORECASTER BLAKE/STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      27/0300Z 19.7N  46.1W    45 KT
 12HR VT     27/1200Z 20.8N  46.4W    45 KT
 24HR VT     28/0000Z 22.4N  47.4W    45 KT
 36HR VT     28/1200Z 24.0N  48.4W    50 KT
 48HR VT     29/0000Z 25.4N  49.1W    55 KT
 72HR VT     30/0000Z 27.5N  50.0W    65 KT
 96HR VT     01/0000Z 29.0N  50.5W    65 KT
120HR VT     02/0000Z 31.0N  51.0W    65 KT


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