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TROPICAL STORM LISA DISCUSSION NUMBER   2
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT MON OCT 05 1998

LOCATING THE CENTER ON SHEARED TROPICAL CYCLONES WITH INFRARED
IMAGERY IS USUALLY QUITE DIFFICULT...AND THIS ONE IS NO EXCEPTION. 
HOWEVER THE TROPICAL PREDICTION CENTERS INFRARED COMBINATION CHANNEL
IMAGERY REVEALS ENOUGH OF THE LOW CLOUD LINES OVER THE WESTERN
SEMICIRCLE SO THAT THE CENTER IS ESTIMATED NEAR THE SOUTHWEST EDGE
OF THE MAIN DENSE OVERCAST.  THIS LOCATION GIVES A SLIGHTLY SLOWER
FORWARD SPEED...305/10.  THE NCEP GLOBAL MODEL SHOWS A HIGH
AMPLITUDE MID-TROPOSPHERIC PATTERN...WITH A MAJOR TROUGH DIGGING IN
THE WEST-CENTRAL ATLANTIC DURING THE NEXT COUPLE OF DAYS. 
CONSISTENT WITH THIS STEERING PATTERN...THE TRACK GUIDANCE MODELS
SHOW A TURN TOWARD THE NORTH AND NORTHEAST...AND SO DOES THE
OFFICIAL FORECAST.  THIS IS QUITE SIMILAR TO THE TRACK FORECAST FROM
THE PREVIOUS PACKAGE. 

AN UPPER-LEVEL LOW IN THE VICINITY OF 21N 54W IS CONTRIBUTING TO
SOUTHWESTERLY VERTICAL SHEAR OVER THE TROPICAL STORM.  CURRENT
INTENSITY ESTIMATE REMAINS NEAR 40 KNOTS.  LISA HAS A FAIRLY LARGE
CIRCULATION AND IT MAY BE MORE RESILIENT TO SHEAR THAN A VERY SMALL
STORM...WHICH WOULD PROBABLY BE DISSIPATING IN SUCH AN ENVIRONMENT. 
HOWEVER THE SHEARING IS NOT EXPECTED TO RELAX SO STRENGTHENING IS
NOT LIKELY.  LATE IN THE FORECAST PERIOD OR BEYOND...LISA MAY BE
INTERACTING WITH A FRONTAL ZONE AND COULD UNDERGO SOME BAROCLINIC
DEVELOPMENT.

PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     06/0300Z 16.7N  49.7W    40 KTS
12HR VT     06/1200Z 17.5N  51.0W    40 KTS
24HR VT     07/0000Z 19.5N  52.0W    35 KTS
36HR VT     07/1200Z 21.5N  50.5W    35 KTS
48HR VT     08/0000Z 23.0N  48.5W    35 KTS
72HR VT     09/0000Z 26.5N  43.0W    35 KTS
 
 
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