Hurricane CALVIN

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HURRICANE CALVIN DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP032011
200 AM PDT SAT JUL 09 2011
 
INFRARED SATELLITE IMAGERY INDICATES THAT CALVIN HAS MAINTAINED A
RAGGED AND IRREGULARLY SHAPED CENTRAL DENSE OVERCAST DURING THE
PAST SEVERAL HOURS. HOWEVER...THE COVERAGE AND INTENSITY OF THE
ASSOCIATED DEEP CONVECTION HAS BEEN DECREASING.  UW-CIMSS AND SHIPS
MODEL ANALYSES ALSO INDICATE MODEST EASTERLY SHEAR CONTINUING TO
AFFECT CALVIN...AND THE WESTWARD DISPLACEMENT OF THE MAIN
CONVECTIVE MASS RELATIVE TO THE CENTER IN CONVENTIONAL AND
MICROWAVE IMAGERY SEEMS TO CONFIRM THIS.  BASED UPON THE SLIGHTLY
DEGRADED SATELLITE PRESENTATION AND A BLEND OF DVORAK T- AND
CI-NUMBERS FROM TAFB/SAB...THE INITIAL INTENSITY IS LOWERED TO 65
KT.  CALVIN HAS ALREADY REACHED A STRONG GRADIENT OF SEA SURFACE
TEMPERATURES AND WILL BE MOVING OVER SSTS LESS THAN 25C AFTER 24
HOURS. THIS...IN COMBINATION WITH A MORE STABLE LOWER TROPOSPHERE
AND A CONTINUATION OF THE EASTERLY SHEAR...SHOULD RESULT IN STEADY
WEAKENING TO A REMNANT LOW IN ABOUT 48 HOURS AND DISSIPATION WITHIN
96 HOURS. THIS REASONING IS REFLECTED IN THE NHC OFFICIAL FORECAST
WHICH IS ADJUSTED DOWNWARD IN AGREEMENT WITH A BLEND OF DYNAMICAL
AND STATISTICAL MODEL OUTPUT.

LATEST CENTER FIXES SUGGEST THAT CALVIN HAS BEEN SLOWING DOWN....AND
THE INITIAL MOTION ESTIMATE IS 285/09. A MID-TROPOSPHERIC RIDGE
EXTENDING FROM THE SOUTHERN PLAINS TO THE SUBTROPICAL EASTERN
PACIFIC IS EXPECTED TO STEER CALVIN ON A GENERALLY WEST-
NORTHWESTWARD TRACK DURING THE NEXT DAY OR TWO.  AS CALVIN BECOMES
AN INCREASINGLY SHALLOW SYSTEM AFTER THAT...IT WILL DECOUPLE FROM
THE DEEP-LAYER FLOW AND DECELERATE FURTHER AS IT ENCOUNTERS WEAKER
LOW-LEVEL WINDS. THE NEW FORECAST IS BASICALLY AN UPDATE OF
THE PREVIOUS ONE AND IS VERY NEAR THE MULTI-MODEL TVCN CONSENSUS.

THE WIND RADII IN ALL QUADRANTS WERE MODIFIED BASED ON A 0505 UTC
ASCAT PASS.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  09/0900Z 16.9N 110.1W   65 KT  75 MPH
 12H  09/1800Z 17.3N 111.6W   55 KT  65 MPH
 24H  10/0600Z 17.7N 113.2W   45 KT  50 MPH
 36H  10/1800Z 18.2N 114.5W   35 KT  40 MPH
 48H  11/0600Z 18.7N 115.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  12/0600Z 19.5N 117.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  13/0600Z...DISSIPATED
 
$$
FORECASTER KIMBERLAIN
 
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