000 WTPZ43 KNHC 090841 TCDEP3 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 000 WTPZ43 KNHC 090841 TCDEP3 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