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