Tropical Storm CALVIN

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TROPICAL STORM CALVIN DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP032011
800 PM PDT THU JUL 07 2011
 
CONVENTIONAL SATELLITE IMAGERY INDICATES THE CLOUD PATTERN WENT
THROUGH A BRIEF BURSTING PHASE EARLIER THIS AFTERNOON...BUT HAS
SINCE DECREASED IN BOTH VERTICAL EXTENT AND AREAL COVERAGE.
SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE T3.0/45 KT AND
T2.5/35 KT...RESPECTIVELY...AND UW-CIMSS ADT VALUES ARE T2.9/43 KT.
MICROWAVE SATELLITE DATA INDICATE THE MID-LEVEL CIRCULATION CENTER
IS SHEARED AT LEAST 45 NMI TO THE NORTHWEST OF THE LOW-LEVEL
CENTER. THEREFORE...THE INITIAL INTENSITY HAS ONLY BEEN INCREASED TO
35 KT DESPITE THE HIGHER INTENSITY ESTIMATES...WHICH STILL MAKES
THE CYCLONE THE THIRD TROPICAL STORM OF THE SEASON. UPPER-LEVEL
OUTFLOW REMAINS GOOD IN THE WESTERN SEMICIRCLE BUT RESTRICTED
ELSEWHERE.
 
THE INITIAL MOTION ESTIMATE OF 290/12 IS BASED ON EXTRAPOLATION...
CONTINUITY WITH THE PREVIOUS FORECAST...AND EARLIER MICROWAVE FIXES.
CALVIN IS EXPECTED TO REMAIN EMBEDDED WITHIN DEEP-LAYER
EAST-SOUTHEASTERLY FLOW ALONG THE SOUTHERN PERIPHERY OF A LARGE
SUBTROPICAL RIDGE THAT EXTENDS FROM THE U.S. SOUTHERN PLAINS
WESTWARD ACROSS NORTHERN AND CENTRAL MEXICO. THE GLOBAL MODELS
BASICALLY MAINTAIN THE STRENGTH AND POSITION OF THE RIDGE
THROUGHOUT THE FORECAST PERIOD...WHICH SHOULD KEEP CALVIN MOVING IN
A GENERAL WEST-NORTHWESTWARD DIRECTION. AS MENTIONED IN THE
PREVIOUS DISCUSSION...THE HWRF...GFDL...AND GFDN MODELS TAKE THE
CYCLONE NORTHWARD INTO A WEAKENING RIDGE BY 36 HOURS...WHICH
APPEARS UNLIKELY GIVEN THE CURRENT STRENGTH OF THE RIDGE. THESE
MODELS ARE...THEREFORE...CONSIDERED TO BE OUTLIER SOLUTIONS. BY 72
HOURS...CALVIN IS EXPECTED TO WEAKEN INTO A SHALLOW REMNANT LOW
PRESSURE SYSTEM AS IT MOVES OVER 23C SSTS...AND BE STEERED MORE
WESTWARD BY LOW-LEVEL EASTERLY TRADE WINDS. THE OFFICIAL FORECAST
TRACK IS JUST AN EXTENSION OF THE PREVIOUS ADVISORY TRACK AND LIES
NEAR THE MIDDLE OF THE GLOBAL MODELS ENVELOPE.
 
EASTERLY VERTICAL WIND SHEAR OF 20 KT IS FORECAST TO WEAKEN TO NEAR
10 KT BY 24-36 HOURS...WHICH SHOULD ALLOW THE CYCLONE TO GRADUALLY
STRENGTHEN. HOWEVER...THE MOST FAVORABLE UPPER-LEVEL OUTFLOW
PATTERN IS NOT EXPECTED TO OCCUR UNTIL AFTER 48 HOURS...AT WHICH
TIME CALVIN IS FORECAST TO BE OVER MUCH COOLER WATER. THE OFFICIAL
INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND IS A
BLEND OF THE SHIPS AND LGEM INTENSITY MODELS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  08/0300Z 16.0N 104.3W   35 KT  40 MPH
 12H  08/1200Z 16.6N 105.7W   40 KT  45 MPH
 24H  09/0000Z 17.4N 107.6W   50 KT  60 MPH
 36H  09/1200Z 18.0N 109.2W   55 KT  65 MPH
 48H  10/0000Z 18.5N 110.4W   45 KT  50 MPH
 72H  11/0000Z 19.4N 112.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  12/0000Z 20.5N 116.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  13/0000Z...DISSIPATED
 
$$
FORECASTER STEWART
 
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