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| #381975 (Received by flhurricane at: 4:39 AM 09.Oct.2010) TCDAT2 HURRICANE OTTO DISCUSSION NUMBER 13 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL172010 500 AM AST SAT OCT 09 2010 OTTO CONTINUES TO PRODUCE DEEP CONVECTION IN A CDO WITH CLOUD TOPS COLDER THAN -80C...HOWEVER THE CLOUD PATTERN IS BECOMING INCREASINGLY DISTORTED DUE TO 20 TO 25 KT OF SOUTHWESTERLY SHEAR. THIS SHEAR IS ALSO TILTING THE VORTEX NORTHEASTWARD WITH HEIGHT AS SEEN IN A 0021 UTC SSMIS PASS. THE INITIAL INTENSITY OF 75 KT IS BASED ON A BLEND OF DVORAK FINAL-T AND CI NUMBERS OF 4.0 TO 5.0 FROM TAFB AND SAB. SLOW WEAKENING IS EXPECTED OVER THE NEXT DAY OR SO WHILE OTTO REMAINS A TROPICAL CYCLONE DUE TO SHEAR AND DECREASING SEA SURFACE TEMPERATURES. GRADUAL WEAKENING SHOULD CONTINUE BEYOND THAT TIME AS OTTO UNDERGOES EXTRATROPICAL TRANSITION. THE INITIAL MOTION ESTIMATE OF 055/21 IS UNCERTAIN DUE TO A LACK OF RECENT MICROWAVE IMAGERY...AND IS BASED ON THE ASSUMPTION THAT THE LOW-LEVEL CENTER CONTINUES TO LAG BEHIND THE COLDEST CLOUD TOPS. OTTO WILL CONTINUE ACCELERATING NORTHEASTWARD OVER THE NEXT COUPLE OF DAYS BETWEEN A LARGE DEEP-LAYER TROUGH OFF THE COAST OF NORTH AMERICA AND A SUBTROPICAL RIDGE OVER THE EASTERN TROPICAL ATLANTIC. THE OFFICIAL FORECAST IS A BLEND OF THE PREVIOUS PACKAGE AND THE TVCN MULTI-MODEL CONSENSUS THROUGH 48 HOURS. BEYOND THAT TIME... MOST OF THE GLOBAL MODELS AND THE GFS ENSEMBLE MEAN SUGGEST THAT POST-TROPICAL OTTO WILL MOVE AROUND THE TOP OF A SHORTWAVE RIDGE AND TURN SOUTHEASTWARD IN THE VICINITY OF THE AZORES. HOWEVER... THERE ARE DIFFERENCES IN BOTH THE SHARPNESS OF THE SOUTHEASTWARD TURN AND THE FORWARD SPEED. THE OFFICIAL FORECAST HAS BEEN ADJUSTED SOUTHWARD AND WESTWARD AT DAYS 4 AND 5 TOWARD A BLEND OF THE UKMET AND GFS MODELS...BUT CONFIDENCE IS LOWER THAN NORMAL AT THESE TIMES DUE TO THE LARGE SPREAD IN THE GUIDANCE. THE INITIAL 34-KT WIND RADII WERE ADJUSTED BASED ON A 0052 UTC ASCAT PASS. FORECAST POSITIONS AND MAX WINDS INITIAL 09/0900Z 29.2N 58.5W 75 KT 12HR VT 09/1800Z 31.1N 54.8W 70 KT 24HR VT 10/0600Z 34.3N 48.3W 70 KT 36HR VT 10/1800Z 37.7N 40.8W 65 KT 48HR VT 11/0600Z 41.3N 33.4W 55 KT...POST-TROP/EXTRATROP 72HR VT 12/0600Z 43.0N 27.0W 45 KT...POST-TROP/EXTRATROP 96HR VT 13/0600Z 40.5N 24.5W 40 KT...POST-TROP/EXTRATROP 120HR VT 14/0600Z 37.0N 22.0W 40 KT...POST-TROP/EXTRATROP $$ FORECASTER BRENNAN |
