000
WTNT44 KNHC 220233
TCDAT4
TROPICAL STORM LISA DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142010
1100 PM EDT TUE SEP 21 2010
  
CONVENTIONAL SATELLITE AND MICROWAVE IMAGES INDICATE THAT LISA HAS
GENERALLY CHANGED LITTLE IN STRUCTURE DURING THE PAST FEW
HOURS...ALTHOUGH CLOUD TOPS HAVE WARMED SOME.  SATELLITE INTENSITY
ESTIMATES ARE 45 KT AND 35 KT FROM TAFB AND SAB...RESPECTIVELY...
AND THE THE INITIAL WIND SPEED IS HELD AT 40 KT FOR THIS ADVISORY.
LISA HAS AN OPPORTUNITY TO STRENGTHEN DURING THE NEXT COUPLE OF
DAYS AS IT REMAINS IN A RELATIVELY LOW WIND SHEAR ENVIRONMENT AND
OVER SEA SURFACE TEMPERATURES NEAR 27 C. WESTERLY SHEAR...
ASSOCIATED WITH A MID- TO UPPER-LEVEL TROUGH...IS EXPECTED TO
INCREASE SIGNIFICANTLY IN ABOUT 3 DAYS.  THIS...COMBINED WITH DRY
AIR...SHOULD CAUSE STEADY WEAKENING BY THE END OF THE FORECAST
PERIOD.  THE OFFICIAL FORECAST IS HIGHER THAN ALL OF THE GUIDANCE
FOR THE NEXT COUPLE DAYS...GIVEN THE APPARENTLY FAVORABLE
ENVIRONMENTAL CONDITIONS IN THE SHORT TERM...AND THEN FOLLOWS A
BLEND OF THE LGEM AND SHIPS MODELS. 

LISA APPEARS TO HAVE JOGGED TO THE EAST OVER THE PAST FEW
HOURS...AND THE LATEST 12-HOUR INITIAL MOTION ESTIMATE IS 040/2. 
THE STORM REMAINS IN WEAK STEERING CURRENTS NEAR THE BASE OF A
LARGE AND AMPLIFIED DEEP-LAYER TROUGH OVER THE EASTERN ATLANTIC.  A
SLOW AND LIKELY ERRATIC NORTH TO NORTH-NORTHWESTWARD MOTION IS
EXPECTED DURING THE NEXT DAY OR SO AS THE UPPER TROUGH REMAINS IN
PLACE.  BEYOND A COUPLE OF DAYS...A GRADUAL TURN TO THE
WEST-NORTHWEST IS FORECAST AS THE TROUGH CUTS OFF AND LOW- TO
MID-LEVEL RIDGING BUILDS TO THE NORTH OF LISA.  THE TRACK MODEL
GUIDANCE REMAINS IN POOR AGREEMENT AND THIS FORECAST IS OF LOW
CONFIDENCE.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      22/0300Z 18.2N  31.3W    40 KT
 12HR VT     22/1200Z 18.3N  31.3W    50 KT
 24HR VT     23/0000Z 18.5N  31.4W    55 KT
 36HR VT     23/1200Z 18.7N  31.6W    60 KT
 48HR VT     24/0000Z 19.1N  32.3W    65 KT
 72HR VT     25/0000Z 19.7N  33.5W    55 KT
 96HR VT     26/0000Z 20.5N  35.5W    45 KT
120HR VT     27/0000Z 21.0N  38.0W    35 KT
 
$$
FORECASTER CANGIALOSI