Tropical Storm CALVIN

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TROPICAL STORM CALVIN DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP032011
200 AM PDT FRI JUL 08 2011
 
SATELLITE IMAGES INDICATE THAT CALVIN HAS MAINTAINED A LARGE AREA OF
COLD CONVECTIVE TOPS DURING THE PAST SEVERAL HOURS...BUT THE SHAPE
OF THE MAIN CONVECTIVE MASS APPEARS DEFORMED.  NEVERTHELESS...THE
OVERALL CLOUD PATTERN APPEARS TO BE A LITTLE MORE ORGANIZED THAN
BEFORE...IN ADDITION TO THE RECENT DEVELOPMENT OF SLIGHTLY BETTER
DEFINED CURVED BANDING FEATURES.  A 0344 UTC ASCAT PASS ALSO SHOWED
SEVERAL BELIEVABLE WIND VECTORS OF AT LEAST 40 KT.  THE CURRENT
INTENSITY ESTIMATE IS INCREASED TO 45 KT FOR THIS ADVISORY IN
AGREEMENT WITH THE LATEST DVORAK SATELLITE ESTIMATES OF 3.0 FROM
TAFB/SAB AND THE EARLIER ASCAT PASS.  ALTHOUGH CALVIN REMAINS IN AN
ENVIRONMENT OF MODEST EASTERLY SHEAR...THE SHEAR IS FORECAST TO
DECREASE SOMEWHAT WITHIN THE NEXT 24 HOURS.  AT THE SAME TIME...
CALVIN WILL BE MOVING AWAY FROM 28-29C WATERS AND TOWARD A REGION OF
SHARPLY LOWER SEA SURFACE TEMPERATURES.  THESE FACTORS SHOULD ALLOW
FOR A NARROW WINDOW OF OPPORTUNITY FOR STRENGTHENING IN THE SHORT-
TERM...FOLLOWED BY A GENERAL WEAKENING TREND.  THE OFFICIAL NHC
INTENSITY IS LITTLE HIGHER THAN BEFORE AND REPRESENTS A BLEND OF
LGEM AND THE INTENSITY MODEL CONSENSUS IVCN.
 
THE INITIAL MOTION IS HARD TO DETERMINE.  BASED UPON A BLEND OF
FIXES FROM GEOSTATIONARY AND MICROWAVE IMAGERY...THE INITIAL MOTION
IS ESTIMATED TO BE 285/13. CALVIN SHOULD BE STEERED ON A WESTWARD TO
WEST-NORTHWESTWARD COURSE DURING THE NEXT FEW DAYS...ON THE SOUTH
SIDE OF A BROAD MID-TROPOSPHERIC RIDGE EXTENDING FROM THE SOUTHERN
PLAINS WESTWARD TO THE SUBTROPICAL EASTERN PACIFIC.  DURING THIS
TIME...THE CYCLONE SHOULD ALSO BEGIN TO DECELERATE AS IT WEAKENS
AND BECOMES SHALLOWER...STEERED BY THE RELATIVELY SLOWER LOW-LEVEL
EASTERLY FLOW.   ALTHOUGH GLOBAL MODELS ARE GENERALLY IN GOOD
AGREEMENT ON THIS SCENARIO...THERE HAS BEEN A SOUTHWARD SHIFT IN
THE GUIDANCE THIS CYCLE. THE NEW FORECAST FOLLOWS THIS SOUTHWARD
TREND AND IS NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE...CLOSE TO
THE DYNAMICAL MODEL CONSENSUS.
  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  08/0900Z 16.3N 105.9W   45 KT  50 MPH
 12H  08/1800Z 16.7N 107.6W   55 KT  65 MPH
 24H  09/0600Z 17.3N 109.4W   60 KT  70 MPH
 36H  09/1800Z 17.9N 111.0W   50 KT  60 MPH
 48H  10/0600Z 18.5N 112.4W   40 KT  45 MPH
 72H  11/0600Z 19.5N 115.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  12/0600Z 20.0N 117.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  13/0600Z...DISSIPATED
 
$$
FORECASTER KIMBERLAIN
 
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