ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM TROPICAL DEPRESSION IRWIN DISCUSSION NUMBER 40 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 800 PM PDT SAT OCT 15 2011 THE STRUCTURE OF IRWIN CONTINUES TO DETERIORATE. THE LOW-LEVEL CENTER RE-FORMED A LITTLE CLOSER TO THE CONVECTION THIS EVENING... BUT THE CONVECTION HAS BEEN SHRINKING WITH ONLY A SMALL AREA OF -50C CLOUD TOPS REMAINING. A DELAYED 1708 UTC ASCAT PASS RECEIVED JUST A FEW HOURS AGO SHOWED MAXIMUM WINDS OF ONLY 20-25 KT IN THE SOUTHWESTERN QUADRANT...AND THE INTENSITY IS CONSERVATIVELY LOWERED TO 30 KT. IRWIN IS NOW MOVING AWAY FROM THE COLD WAKE LEFT BEHIND FROM JOVA TOWARD WARMER WATER...BUT THE DAMAGE MAY ALREADY BE DONE. EAST-NORTHEASTERLY TO EASTERLY SHEAR IS EXPECTED TO INCREASE OVER THE NEXT COUPLE OF DAYS...AND GIVEN THE CURRENT STRUCTURE OF THE DEPRESSION...RE-INTENSIFICATION IS NOT EXPECTED. THE NEW OFFICIAL FORECAST NOW MAKES IRWIN A REMNANT LOW WITHIN 48 HOURS...BUT THIS COULD OCCUR AS EARLY AS SUNDAY IF SUFFICIENT DEEP CONVECTION DOES NOT RE-DEVELOP. THE ECMWF IS THE ONLY MODEL TO DISSIPATE THE SYSTEM...WHICH IT DOES BY DAY 3...SO THE FORECAST CONTINUES TO HOLD OFF DISSIPATION UNTIL DAY 5. IRWIN IS MOVING 200 DEGREES AT 8 KT...CAUGHT BETWEEN A LOW-LEVEL RIDGE THAT EXTENDS FROM NORTHWESTERN MEXICO SOUTHWESTWARD ACROSS THE PACIFIC...AND BROAD CYCLONIC FLOW OVER CENTRAL AMERICA. THE LOW-LEVEL STEERING IS EXPECTED TO COLLAPSE OVER THE NEXT COUPLE OF DAYS...AND IRWIN IS THEREFORE FORECAST TO BECOME NEARLY STATIONARY BY 48 HOURS. THE REMNANT LOW COULD THEN BEGIN TO MOVE A LITTLE FASTER TOWARD THE SOUTHEAST BY DAY 4 AS IT BECOMES INFLUENCED BY STRENGTHENING SOUTHWESTERLY CROSS-EQUATORIAL FLOW. THE NEW OFFICIAL FORECAST IS RELATIVELY UNCHANGED FROM THE PREVIOUS ONE THROUGH 48 HOURS BUT THEN IS A LITTLE FARTHER SOUTHEAST ON DAYS 3 AND 4. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 14.8N 107.3W 30 KT 35 MPH 12H 16/1200Z 14.2N 108.0W 25 KT 30 MPH 24H 17/0000Z 14.0N 108.8W 25 KT 30 MPH 36H 17/1200Z 14.1N 109.5W 25 KT 30 MPH 48H 18/0000Z 14.2N 109.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 19/0000Z 13.5N 109.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 20/0000Z 13.0N 108.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 21/0000Z...DISSIPATED $$ FORECASTER BERG NNNN
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Page last modified: Tuesday, 17-Jul-2012 13:44:20 UTC