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Tropical Storm SONIA Forecast Discussion Number 9
2013-11-03 09:44:20| National Hurricane Center (East Pacific)
Issued at 100 AM PST SUN NOV 03 2013 000 WTPZ43 KNHC 030844 TCDEP3 TROPICAL STORM SONIA DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182013 100 AM PST SUN NOV 03 2013 AFTER HAVING GONE THROUGH SEVERAL PULSING PHASES OF CONVECTIVE DEVELOPMENT DURING THE PAST COUPLE OF DAYS...MORE PERSISTENT AND ORGANIZED DEEP CONVECTION HAS OCCURRED SINCE THE PREVIOUS ADVISORY DUE TO A SHARP DECREASE IN THE VERTICAL WIND SHEAR. ASCAT-A AND ASCAT-B OVERPASSES AT 0421Z AND 0514Z...RESPECTIVELY...INDICATED BELIEVABLE 30-34 KT WIND VECTORS IN THE NORTHWEST QUADRANT. THESE WINDS ARE ALSO SUPPORTED BY SATELLITE INTENSITY ESTIMATES OF 35 KT FROM TAFB AND 36 KT FROM THE UW-CIMSS SATCON. AS A RESULT...THE DEPRESSION HAS BEEN UPGRADED TO TROPICAL STORM SONIA. THE VERTICAL SHEAR IS FORECAST TO REMAIN LESS THAN 10 KT FOR THE NEXT 12 HOURS OR SO...WHICH SHOULD ALLOW FOR SOME ADDITIONAL STRENGTHENING DURING THAT TIME. HOWEVER...BY 24 HOURS AND BEYOND...THE WIND SHEAR IS EXPECTED TO INCREASE FROM THE SOUTHWEST AT MORE THAN 25 KT... CAUSING RAPID WEAKENING TO OCCUR...ESPECIALLY BY 36 HOURS WHEN THE SYSTEM IS INTERACTING WITH THE MOUNTAINOUS TERRAIN OF MEXICO. ALTHOUGH A POSITION IS SHOWN AT 48 HOURS...MAINLY FOR CONTINUITY... THE SYSTEM WILL LIKELY HAVE DISSIPATED INLAND BY THAT TIME. THE INITIAL MOTION ESTIMATE IS 360/06 KT. THE TWO AFOREMENTIONED ASCAT OVERPASSES...ALONG WITH PASSIVE MICROWAVE SATELLITE IMAGERY...HAVE HELPED SIGNIFICANTLY WITH THE CENTER LOCATION THIS MORNING. HOWEVER...SINCE THE OVERALL INNER-CORE WIND FIELD IS STILL BROAD AND CONVECTION CONTINUES TO DEVELOP OVER AND NORTH OF THE ALLEGED CENTER...SOME ERRATIC MOTION IN A GENERAL NORTHWARD DIRECTION COULD OCCUR DURING THE NEXT 6 HOURS OR SO. BY 12 HOURS AND BEYOND...SONIA WILL GRADUALLY COME UNDER THE INFLUENCE OF INCREASING SOUTHWESTERLY STEERING FLOW AHEAD OF AN APPROACHING BROAD MID-/UPPER-LEVEL TROUGH THAT IS CURRENTLY PASSING 120W LONGITUDE. AS A RESULT...SONIA SHOULD BEGIN TO ACCELERATE AND TURN TOWARD THE NORTH-NORTHEAST BY THIS AFTERNOON OR EVENING...AND CONTINUE TO ACCELERATE TO THE NORTH-NORTHEAST OR NORTHEAST UNTIL LANDFALL OCCURS ON MONDAY. THE NHC MODELS ARE NOW IN EXCELLENT AGREEMENT ON THIS SCENARIO....AND THE NEW TRACK FORECAST IS SIMILAR TO BUT SLIGHTLY TO THE RIGHT OF THE PREVIOUS ADVISORY TRACK AND TO THE LEFT OF THE CONSENSUS MODEL TVCE. BASED ON THE UPDATED TRACK AND INTENSITY FORECASTS...THE GOVERNMENT OF MEXICO HAS ISSUED A TROPICAL STORM WARNING FOR THE COAST OF WEST-CENTRAL MEXICO FROM MAZATLAN TO ALTATA. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 18.8N 110.0W 35 KT 40 MPH 12H 03/1800Z 20.3N 109.7W 40 KT 45 MPH 24H 04/0600Z 22.6N 108.3W 35 KT 40 MPH 36H 04/1800Z 24.9N 106.6W 30 KT 35 MPH...INLAND 48H 05/0600Z 27.0N 105.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 72H 06/0600Z...DISSIPATED $$ FORECASTER STEWART
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