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Tropical Storm ALVIN Forecast Discussion Number 3
2013-05-16 04:47:46| National Hurricane Center (East Pacific)
Issued at 800 PM PDT WED MAY 15 2013 000 WTPZ41 KNHC 160247 TCDEP1 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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