Tropical Storm CALVIN

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TROPICAL STORM CALVIN DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
8 AM PDT MON JUN 27 2005
 
ON SATELLITE IMAGES...THE ORGANIZATION OF THE DEEP CONVECTION IS NOT
IMPRESSIVE AT THIS TIME. HOWEVER...RADAR IMAGES FROM THE COMISION
NACIONAL DEL AGUA ACAPULCO REVEAL A RATHER WELL-DEFINED SPIRAL RAIN
BAND STRUCTURE. THE INTENSITY IS INCREASED TO 45 KT FOR THIS
ADVISORY IN AGREEMENT WITH THE LATEST DVORAK ESTIMATES.  CALVIN IS
IN A MODERATE EASTERLY SHEAR ENVIRONMENT...SO ONLY SLOW
STRENGTHENING IS EXPECTED. THE OFFICIAL WIND SPEED FORECAST IS
SIMILAR TO THAT FROM THE PREVIOUS PACKAGE AND IS IN GENERAL
AGREEMENT WITH THE SHIPS GUIDANCE. BY 72 HOURS...THE CYCLONE WILL
BEGIN TO MOVE OVER COOLER WATERS...SO WEAKENING IS PROBABLE AFTER
THAT TIME.

CALVIN HAS BEGUN TO TURN TOWARD THE LEFT AND THE MOTION ESTIMATE IS
NOW 310/7.  SYNOPTIC REASONING FOR THE TRACK FORECAST IS ABOUT THE
SAME AS IN THE PREVIOUS ADVISORY.  A MID-LEVEL RIDGE TO THE NORTH
OF THE TROPICAL CYCLONE SHOULD INDUCE A MOSTLY WEST-NORTHWESTWARD
MOTION UNTIL LATE IN THE PERIOD...WHEN A MORE WESTWARD TRACK OF THE
WEAKENING CYCLONE...FOLLOWING THE LOW-LEVEL EASTERLIES...IS LIKELY.
 
THE LEFTWARD TURN REDUCES THE THREAT TO THE COAST...AND IF A MORE
WEST-NORTHWESTWARD MOTION IS ESTABLISHED...THE TROPICAL STORM WATCH
COULD BE DISCONTINUED LATER TODAY.  LOCALLY HEAVY RAINFALL IS
EXPECTED TO CONTINUE TO AFFECT PORTIONS OF THE SOUTHERN COAST OF
MEXICO TODAY.
 
FORECASTER PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/1500Z 14.8N  99.5W    45 KT
 12HR VT     28/0000Z 15.3N 100.2W    50 KT
 24HR VT     28/1200Z 15.9N 102.1W    50 KT
 36HR VT     29/0000Z 16.5N 104.3W    55 KT
 48HR VT     29/1200Z 17.1N 106.5W    55 KT
 72HR VT     30/1200Z 18.0N 110.0W    55 KT
 96HR VT     01/1200Z 18.5N 113.5W    35 KT
120HR VT     02/1200Z 18.5N 116.5W    25 KT
 
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