000 WTNT41 KNHC 291446 TCDAT1 TROPICAL STORM ARLENE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL012011 1000 AM CDT WED JUN 29 2011 THE CLOUD PATTERN OF THE TROPICAL STORM IS GRADUALLY BECOMING BETTER ORGANIZED THIS MORNING...WITH MORE EVIDENCE OF CONVECTIVE BANDING. THE CURRENT INTENSITY IS SET AT 45 KT...WHICH IS IN CLOSE AGREEMENT WITH SFMR-OBSERVED SURFACE WIND MEASUREMENTS FROM THE AIR FORCE HURRICANE HUNTERS. WATER VAPOR IMAGERY INDICATES THAT THE UPPER-LEVEL WINDS ARE BECOMING MORE CONDUCIVE FOR STRENGTHENING. THE CURRENT LACK OF A WELL-DEFINED INNER CORE WOULD ARGUE AGAINST SIGNIFICANT STRENGTHENING OVER THE NEXT 24 HOURS. HOWEVER...THE SHIPS RAPID INTENSIFICATION INDEX SHOWS A SIGNIFICANTLY HIGH PROBABILITY OF A 25 TO 30 KT INCREASE IN INTENSITY OVER THE NEXT 24 HOURS. THEREFORE THE OFFICIAL INTENSITY FORECAST IS ABOVE MOST OF THE GUIDANCE AND NOW SHOWS ARLENE APPROACHING HURRICANE STRENGTH AT LANDFALL. BASED ON THE NEW INTENSITY FORECAST...A HURRICANE WATCH HAS BEEN ISSUED FOR A PORTION OF THE COAST OF NORTHEASTERN MEXICO. CENTER FIXES FROM THE AIRCRAFT INDICATE THAT ARLENE WAS LOCATED FARTHER SOUTH THAN PREVIOUSLY ESTIMATED...WHICH REQUIRES SOME SOUTHWARD RELOCATION FOR THIS ADVISORY. BASED ON THE LATEST FIXES...THE INITIAL MOTION ESTIMATE IS NOW WEST OR 270/7. A DEEP-LAYER RIDGE TO THE NORTH AND NORTHWEST OF ARLENE SHOULD INDUCE A WESTWARD OR SLIGHTLY SOUTH OF WESTWARD TRACK FOR THE NEXT DAY OR TWO. SOME OF THE MODEL GUIDANCE SUGGESTS EVEN MORE OF A TURN TO THE LEFT AS THE CENTER NEARS THE COAST. THE OFFICIAL TRACK FORECAST IS MORE OR LESS BETWEEN THE GFS AND ECMWF TRACKS. GIVEN THE LARGE SIZE OF THE CIRCULATION OF ARLENE...ONE SHOULD NOT FOCUS ON THE EXACT FORECAST TRACK...AS IMPACTS WILL LIKELY BE FELT OVER A LARGE PORTION OF NORTHEASTERN MEXICO WELL AWAY FROM THE CENTER. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 21.2N 95.7W 45 KT 50 MPH 12H 30/0000Z 21.2N 96.6W 50 KT 60 MPH 24H 30/1200Z 21.2N 97.7W 60 KT 70 MPH...INLAND 36H 01/0000Z 21.0N 98.8W 35 KT 40 MPH...INLAND 48H 01/1200Z 20.8N 100.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 02/1200Z...DISSIPATED $$ FORECASTER PASCH/BEVEN 000 WTNT41 KNHC 291446 TCDAT1 TROPICAL STORM ARLENE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL012011 1000 AM CDT WED JUN 29 2011 THE CLOUD PATTERN OF THE TROPICAL STORM IS GRADUALLY BECOMING BETTER ORGANIZED THIS MORNING...WITH MORE EVIDENCE OF CONVECTIVE BANDING. THE CURRENT INTENSITY IS SET AT 45 KT...WHICH IS IN CLOSE AGREEMENT WITH SFMR-OBSERVED SURFACE WIND MEASUREMENTS FROM THE AIR FORCE HURRICANE HUNTERS. WATER VAPOR IMAGERY INDICATES THAT THE UPPER-LEVEL WINDS ARE BECOMING MORE CONDUCIVE FOR STRENGTHENING. THE CURRENT LACK OF A WELL-DEFINED INNER CORE WOULD ARGUE AGAINST SIGNIFICANT STRENGTHENING OVER THE NEXT 24 HOURS. HOWEVER...THE SHIPS RAPID INTENSIFICATION INDEX SHOWS A SIGNIFICANTLY HIGH PROBABILITY OF A 25 TO 30 KT INCREASE IN INTENSITY OVER THE NEXT 24 HOURS. THEREFORE THE OFFICIAL INTENSITY FORECAST IS ABOVE MOST OF THE GUIDANCE AND NOW SHOWS ARLENE APPROACHING HURRICANE STRENGTH AT LANDFALL. BASED ON THE NEW INTENSITY FORECAST...A HURRICANE WATCH HAS BEEN ISSUED FOR A PORTION OF THE COAST OF NORTHEASTERN MEXICO. CENTER FIXES FROM THE AIRCRAFT INDICATE THAT ARLENE WAS LOCATED FARTHER SOUTH THAN PREVIOUSLY ESTIMATED...WHICH REQUIRES SOME SOUTHWARD RELOCATION FOR THIS ADVISORY. BASED ON THE LATEST FIXES...THE INITIAL MOTION ESTIMATE IS NOW WEST OR 270/7. A DEEP-LAYER RIDGE TO THE NORTH AND NORTHWEST OF ARLENE SHOULD INDUCE A WESTWARD OR SLIGHTLY SOUTH OF WESTWARD TRACK FOR THE NEXT DAY OR TWO. SOME OF THE MODEL GUIDANCE SUGGESTS EVEN MORE OF A TURN TO THE LEFT AS THE CENTER NEARS THE COAST. THE OFFICIAL TRACK FORECAST IS MORE OR LESS BETWEEN THE GFS AND ECMWF TRACKS. GIVEN THE LARGE SIZE OF THE CIRCULATION OF ARLENE...ONE SHOULD NOT FOCUS ON THE EXACT FORECAST TRACK...AS IMPACTS WILL LIKELY BE FELT OVER A LARGE PORTION OF NORTHEASTERN MEXICO WELL AWAY FROM THE CENTER. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 21.2N 95.7W 45 KT 50 MPH 12H 30/0000Z 21.2N 96.6W 50 KT 60 MPH 24H 30/1200Z 21.2N 97.7W 60 KT 70 MPH...INLAND 36H 01/0000Z 21.0N 98.8W 35 KT 40 MPH...INLAND 48H 01/1200Z 20.8N 100.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 02/1200Z...DISSIPATED $$ FORECASTER PASCH/BEVEN