000 WTPZ43 KNHC 080848 TCDEP3 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 000 WTPZ43 KNHC 080848 TCDEP3 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