ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM IRWIN DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 800 PM PDT THU OCT 06 2011 IRWIN HAS CONTINUED TO STRENGTHEN DURING THE PAST SEVERAL HOURS. A TRMM OVERPASS NEAR 2000 UTC INDICATED A WELL-ORGANIZED LOW-LEVEL CIRCULATION CENTER...AND SINCE THAT TIME THE CLOUD TOPS HAVE BEEN COOLING IN WHAT APPEARS TO BE A DEVELOPING EYEWALL. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE NOW 55 KT. THE INITIAL INTENSITY IS THUS INCREASED TO 55 KT...AND THIS COULD BE CONSERVATIVE. THE CIRRUS OUTFLOW IS GOOD TO EXCELLENT OVER THE NORTHWESTERN SEMICIRCLE. THE INITIAL MOTION IS AGAIN A LITTLE FASTER THAN BEFORE AT 295/9. IRWIN IS ON THE SOUTH SIDE OF A MID-LEVEL RIDGE THAT IS FORECAST TO WEAKEN AS A LARGE DEEP-LAYER TROUGH OVER THE WESTERN UNITED STATES DIGS SOUTHWARD. THIS...IN COMBINATION WITH A LARGE AREA OF DEVELOPING WESTERLY LOW-LEVEL FLOW ASSOCIATED WITH IRWIN AND TROPICAL STORM JOVA TO THE EAST...IS EXPECTED TO STOP THE CURRENT MOTION WITHIN 24-36 HOURS. AFTER THAT...THE TRACK FORECAST GUIDANCE IS IN GOOD AGREEMENT THAT IRWIN SHOULD MOVE EAST-NORTHEASTWARD...ALTHOUGH THERE IS A SIGNIFICANT SPREAD IN THE SPEED BETWEEN THE FASTER GFS AND THE SLOWER ECMWF/UKMET. THE NEW FORECAST TRACK IS SHIFTED TO THE WEST DURING THE FIRST 48 HOURS BASED ON THE CURRENT POSITION AND MOTION. AFTER THAT...IT IS SIMILAR TO THE PREVIOUS FORECAST. AT THIS TIME...IT APPEARS THAT IRWIN AND JOVA ARE FAR ENOUGH APART THAT THERE WILL NOT BE ANY DIRECT INTERACTION BETWEEN THE STORMS TO AFFECT THE MOTION. IRWIN IS CURRENTLY IN A LIGHT/MODERATE VERTICAL WINDS SHEAR ENVIRONMENT OVER SEA SURFACE TEMPERATURES OF 28C. THESE...COMBINED WITH THE CURRENT CONVECTIVE ORGANIZATION...ARE FAVORABLE CONDITIONS FOR RAPID INTENSIFICATION. THE RAPID INTENSIFICATION INDEX OF THE SHIPS MODEL SHOWS A 40 PERCENT CHANCE OF OF 25 KT OF STRENGTHENING DURING THE NEXT 24 HOURS...AND THE SHIPS MODEL ITSELF FORECASTS AN 80 KT INTENSITY IN 24 HOURS. BASED ON THIS...THE INTENSITY FORECAST DURING THE FIRST 48 HOURS IS INCREASED CONSIDERABLY FROM THE PREVIOUS FORECAST. AFTER THAT TIME...THE INTENSITY GUIDANCE NOW SUGGESTS THAT INCREASING EASTERLY SHEAR WILL CAUSE IRWIN TO WEAKEN. BASED ON THIS...THE INTENSITY FORECAST NOW SHOWS A SLOW WEAKENING AFTER 48 HOURS. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 13.4N 119.0W 55 KT 65 MPH 12H 07/1200Z 13.7N 119.3W 65 KT 75 MPH 24H 08/0000Z 14.1N 119.4W 80 KT 90 MPH 36H 08/1200Z 14.4N 119.4W 85 KT 100 MPH 48H 09/0000Z 14.5N 119.0W 85 KT 100 MPH 72H 10/0000Z 14.5N 117.0W 80 KT 90 MPH 96H 11/0000Z 15.5N 113.5W 75 KT 85 MPH 120H 12/0000Z 16.5N 110.5W 70 KT 80 MPH $$ FORECASTER BEVEN NNNN
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Page last modified: Tuesday, 17-Jul-2012 13:44:19 UTC