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Tropical Storm ALVIN Forecast Discussion Number 5
2013-05-16 16:32:21| National Hurricane Center (East Pacific)
Issued at 800 AM PDT THU MAY 16 2013 000 WTPZ41 KNHC 161432 TCDEP1 TROPICAL STORM ALVIN DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012013 800 AM PDT THU MAY 16 2013 ALVIN APPEARS TO HAVE DEGRADED IN STRUCTURE OVERNIGHT. INFRARED SATELLITE IMAGERY AND SCATTEROMETER DATA INDICATE THAT THE CIRCULATION HAS HAD DIFFICULTY SEPARATING FROM THE ITCZ...AND THE LOW-LEVEL CENTER IS LIKELY LOCATED ON THE WESTERN EDGE OF THE DEEP CONVECTION. THE INTENSITY IS BEING HELD AT 45 KT BASED ON THE EARLIER ASCAT DATA...BUT SATELLITE ESTIMATES SUGGEST THAT ALVIN COULD BE A BIT WEAKER. ALTHOUGH THE HISTORICALLY TWO BEST GLOBAL MODELS...THE GFS AND ECMWF...HAVE HAD SOME DISAGREEMENT ON ALVIN...EACH APPEARS TO HAVE BEEN RIGHT TO SOME DEGREE. THE GFS HAD A BETTER HANDLE ON GENESIS...BUT THE ECMWF MAY HAVE BEEN RIGHT THAT ALVIN WOULD NOT STRENGTHEN SIGNIFICANTLY. AS OPPOSED TO YESTERDAY...THE SHIPS GUIDANCE NOW INDICATES THAT 15 TO 20 KT OF VERTICAL SHEAR WILL AFFECT ALVIN DURING THE NEXT FIVE DAYS...AND NEITHER OF THE STATISTICAL MODELS NOW SHOWS THE CYCLONE REACHING HURRICANE STRENGTH. THE PROSPECTS FOR SIGNIFICANT INTENSIFICATION APPEAR TO BE DWINDLING...AND THE OFFICIAL FORECAST ESSENTIALLY HOLDS THE INTENSITY STEADY FOR THE NEXT 48 HOURS. A MORE PRONOUNCED INCREASE IN WESTERLY SHEAR SHOULD BEGIN A DEFINITE WEAKENING TREND BY DAY 3...AND ALVIN COULD DEGENERATE TO A REMNANT LOW NEAR THE END OF THE FORECAST PERIOD. NEEDLESS TO SAY...THERE IS STILL LOW CONFIDENCE IN THE INTENSITY FORECAST. SINCE THE OFFICIAL INTENSITY FORECAST HAS BEEN LOWERED...THE NHC TRACK FORECAST HAS BEEN SHIFTED A BIT FARTHER SOUTH AND WEST WITH THE ASSUMPTION THAT LOWER-LEVEL FLOW WILL HAVE A GREATER INFLUENCE ON STEERING. THE TRACK MODELS ARE IN BETTER AGREEMENT ON THE GENERAL DIRECTION TODAY ALTHOUGH THERE IS STILL A SPEED DISCREPANCY...ESPECIALLY BETWEEN THE GFS AND ECMWF. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 9.4N 107.7W 45 KT 50 MPH 12H 17/0000Z 9.9N 108.8W 50 KT 60 MPH 24H 17/1200Z 10.7N 110.5W 50 KT 60 MPH 36H 18/0000Z 11.2N 112.3W 50 KT 60 MPH 48H 18/1200Z 11.6N 113.6W 50 KT 60 MPH 72H 19/1200Z 13.0N 116.0W 45 KT 50 MPH 96H 20/1200Z 13.5N 118.5W 30 KT 35 MPH 120H 21/1200Z 13.5N 120.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER BERG
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