Tropical Storm ALVIN

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TROPICAL STORM ALVIN DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP012013
800 PM PDT WED MAY 15 2013
 
ALVIN IS STRENGTHENING. SATELLITE DATA DURING THE LAST SEVERAL HOURS
SHOWS A WELL-DEFINED BAND WRAPPING A LITTLE MORE THAN HALFWAY
AROUND THE CIRCULATION. A BURST OF CONVECTION HAS ALSO RECENTLY
FORMED NEAR THE CENTER...POSSIBLY THE BEGINNINGS OF A CENTRAL DENSE
OVERCAST. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB WERE 2.5
AT 0000 UTC. SINCE THAT TIME...HOWEVER...THE CONVECTIVE
ORGANIZATION OF ALVIN HAS INCREASED FURTHER. ON THIS BASIS...THE
INITIAL INTENSITY IS RAISED TO 40 KT.
 
THE INITIAL MOTION ESTIMATE IS 290/11. ALVIN SHOULD CONTINUE MOVING
WEST-NORTHWESTWARD AROUND THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL
RIDGE CENTERED OVER SOUTHERN MEXICO DURING THE NEXT COUPLE OF DAYS.
AFTER THAT TIME...THE MODEL GUIDANCE DIVERGES RATHER SIGNIFICANTLY
AS A RESULT OF DIFFERING MODEL SOLUTIONS REGARDING THE STRENGTH OF
THE VORTEX AND THEIR HANDLING OF A MID- TO UPPER-LEVEL TROUGH
PASSING THROUGH THE SOUTHWESTERN UNITED STATES. THE GFS DEPICTS A
STRONGER SYSTEM THAT FEELS THE EFFECT OF A MORE AMPLIFIED EXTENSION
OF THE ABOVE TROUGH TO THE NORTHWEST OF ALVIN.  ON THE OTHER HAND...
THE UKMET AND ECMWF MAINTAIN A WEAKER SYSTEM AND A LESS AMPLIFIED
TROUGH NORTHWEST OF THE CYCLONE...AND HENCE HAVE A MORE WESTERLY
COURSE.  ALTHOUGH THE OFFICIAL FORECAST GENERALLY SPLITS THE
DIFFERENCE BETWEEN THE GUIDANCE...IT CONTINUES TO LEAN SOMEWHAT
MORE ON THE STRONGER GFS SOLUTION...PLACING THE TRACK FORECAST
SLIGHTLY RIGHT OF THE PREVIOUS ONE AND NEAR THE MULTI-MODEL
CONSENSUS TVCE. GIVEN THE DISPARATE TRACK GUIDANCE...HOWEVER...THE
CONFIDENCE IN THE TRACK FORECAST IS LOWER THAN NORMAL.
 
ALVIN IS FORECAST TO REMAIN IN A FAVORABLE LOCATION TO THE SOUTH OF
AN UPPER-LEVEL RIDGE AXIS DURING THE NEXT DAY OR TWO. THIS SHOULD
PROVIDE A LOW-SHEAR ENVIRONMENT AS THE CYCLONE MOVES OVER VERY WARM
WATERS...LIKELY RESULTING IN ADDITIONAL INTENSIFICATION. IN FACT...
THE SHIPS RAPID INTENSIFICATION INDICATES A NEARLY 1 IN 2 CHANCE OF
A 30-KT INCREASE IN INTENSITY DURING THE NEXT 24 HOURS. AFTER
THAT...THE GFS KEEPS ALVIN IN A LOW SHEAR ENVIRONMENT OVER SLOWLY
DECREASING SEA SURFACE TEMPERATURES UNTIL DAYS 4-5...WHEN THE SHEAR
INCREASES ABRUPTLY. THE ECMWF/UKMET SHOW ALVIN ENCOUNTERING
WESTERLY SHEAR MUCH SOONER...WHICH WOULD STIFLE ANY SIGNIFICANT
INTENSIFICATION. THE NHC INTENSITY FORECAST PLACES MORE WEIGHT ON
THE STRONGER GFS SOLUTION AND REPRESENTS A BLEND OF THE LATEST
SHIPS...DYNAMICAL...AND FSSE GUIDANCE.


FORECAST POSITIONS AND MAX WINDS
 
INIT  16/0300Z  9.0N 105.9W   40 KT  45 MPH
 12H  16/1200Z  9.5N 107.3W   50 KT  60 MPH
 24H  17/0000Z 10.2N 109.0W   60 KT  70 MPH
 36H  17/1200Z 10.9N 110.5W   70 KT  80 MPH
 48H  18/0000Z 11.6N 111.9W   80 KT  90 MPH
 72H  19/0000Z 13.0N 114.0W   75 KT  85 MPH
 96H  20/0000Z 14.7N 116.0W   55 KT  65 MPH
120H  21/0000Z 16.0N 117.3W   35 KT  40 MPH
 
$$
FORECASTER KIMBERLAIN
 
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