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Hurricane LISA


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HURRICANE LISA DISCUSSION NUMBER  19
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142010
500 AM AST SAT SEP 25 2010
 
INFRARED SATELLITE IMAGES INDICATE THAT LISA HAS MAINTAINED A
CENTRAL MASS OF COLD-TOPPED CONVECTION DURING THE LAST SEVERAL
HOURS. HOWEVER...THE CONVECTIVE STRUCTURE ASSOCIATED WITH THE
HURRICANE IS LESS SYMMETRIC THAN IT WAS EARLIER...AND THE OUTFLOW
HAS BECOME RESTRICTED TO THE WEST. AN 0347 UTC AMSU-B PASS ALSO
INDICATED THAT THE LOW- AND MID-LEVEL WERE BEGINNING TO DECOUPLE.
DVORAK T-NUMBERS WERE 3.5 AND 4.5 AT 0600 UTC FROM SAB AND TAFB...
RESPECTIVELY...AND A BLEND OF THESE VALUES IS THE BASIS FOR AN
INITIAL INTENSITY OF 65 KT.  THE RECENT DEGRADATION OF THE CLOUD
PATTERN SUGGESTS THAT UPPER-LEVEL SOUTHWESTERLY FLOW IS IN THE
PROCESS OF INCREASING...AND UW-CIMSS ANALYSES SHOW CLOSE TO 20 KT
OF SHEAR. AS THE CYCLONE GAINS LATITUDE IN THE NEXT DAY OR TWO...IT
SHOULD ENCOUNTER A FURTHER INCREASE IN THE SHEAR AS WELL AS A
DRIER/MORE STABLE AIR MASS AND A COOLER OCEAN SURFACE.  THESE
FACTORS SHOULD CONTRIBUTE TO WEAKENING WHICH COULD POTENTIALLY
OCCUR AT A RAPID PACE. THE NEW NHC INTENSITY FORECAST IS REDUCED
FROM THE PREVIOUS ONE NOW THAT LISA HAS PEAKED AND IS CLOSEST TO
THE DYNAMICAL GUIDANCE.
 
LISA APPEARS TO BE MOVING JUST WEST OF DUE NORTH...AND THE INITIAL
MOTION ESTIMATE IS 355/08. GLOBAL MODELS SHOW THE CYCLONE
SANDWICHED BETWEEN MID-LEVEL HIGH PRESSURE OVER NORTHWEST AFRICA
AND A MID- TO UPPER-LEVEL TROUGH ALONG 35W.  THIS SYNOPTIC PATTERN
SHOULD STEER LISA ON A GENERAL NORTHWARD TRACK DURING THE NEXT
SEVERAL DAYS SO LONG AS IT MAINTAINS VERTICAL INTEGRITY.  AN
ALTERNATE SCENARIO IS FOR A WEAKER LISA...HAVING BECOME A MORE
SHALLOW SYSTEM SOONER THAN FORECAST...TO SLOW AND THEN TURN
SOUTHWESTWARD IN THE LOW-LEVEL TRADES AS DEPICTED IN THE UKMET.  THE
OFFICIAL NHC TRACK FORECAST IS VERY NEAR THE PREVIOUS ONE...
IMMEDIATELY LEFT OF THE MULTI-MODEL CONSENSUS.
  
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      25/0900Z 21.6N  28.1W    65 KT
 12HR VT     25/1800Z 23.1N  28.3W    60 KT
 24HR VT     26/0600Z 24.7N  28.5W    55 KT
 36HR VT     26/1800Z 26.1N  28.6W    50 KT
 48HR VT     27/0600Z 27.4N  28.7W    45 KT
 72HR VT     28/0600Z 29.5N  29.0W    30 KT...POST-TROP/REMNT LOW
 96HR VT     29/0600Z 31.6N  29.5W    25 KT...POST-TROP/REMNT LOW
120HR VT     30/0600Z...DISSIPATED
 
$$
FORECASTER KIMBERLAIN
 
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