ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM IRWIN DISCUSSION NUMBER 23 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 200 PM PDT TUE OCT 11 2011 A BALL OF COLD-TOPPED CONVECTION HAS PERSISTED NEAR THE ESTIMATED CENTER OF IRWIN FOR A WHILE NOW...WITH VISIBLE SATELLITE IMAGERY INDICATING SOME INCREASE IN THE ORGANIZATION OF BANDING FEATURES IN THE LAST FEW HOURS. DVORAK INTENSITY ESTIMATES HAVE INCREASED TO 35 KT AND 45 KT FROM SAB AND TAFB...RESPECTIVELY. GIVEN THAT A 1650 UTC ASCAT OVERPASS SHOWED A FEW 35 KT WIND VECTORS...THE INITIAL INTENSITY IS RAISED TO 40 KT. EVEN THOUGH IRWIN HAS MADE A COMEBACK...ITS LONGER-TERM FUTURE IS NOT AS PROMISING. THE REJUVENATED APPEARANCE OF IRWIN COINCIDES WITH ITS DEPARTURE FROM A NEARBY STRATOCUMULUS FIELD AND ASSOCIATED STABLE AIR MASS. WITH ONLY MODERATE SHEAR FORECAST DURING THE NEXT DAY OR SO...THERE IS SOME LIKELIHOOD OF SHORT-TERM INTENSIFICATION AND THE INTENSITY GUIDANCE REFLECTS THIS. THE CYCLONE IS THEN EXPECTED TO ENTER A HIGH SHEAR ENVIRONMENT DUE TO STRONG LOW-LEVEL WESTERLY FLOW AND EASTERLIES ALOFT IN 2 TO 5 DAYS. THIS PROLONGED EXPOSURE TO SHEAR WILL PROBABLY CAUSE IRWIN TO WEAKEN AND THE CYCLONE IS EXPECTED TO DEGENERATE TO A REMNANT LOW BY AROUND DAY 4. THE OFFICIAL INTENSITY FORECAST IS BASICALLY IN LINE WITH THE STATISTICAL AND INTENSITY CONSENSUS AIDS AND HIGHER THAN THE PREVIOUS ONE THROUGH 48 HOURS TO ACCOUNT FOR CURRENT TRENDS. BEYOND THAT TIME...IT IS ESSENTIALLY THE SAME. THE CENTER APPEARS TO BE FARTHER SOUTH RELATIVE TO THE PREVIOUS ESTIMATE...AND IT IS UNKNOWN WHETHER THIS REPRESENTS A REFORMATION OF THE CENTER OR AN ACTUAL MOVEMENT. THE LATEST FIXES YIELD A LONGER-TERM MOTION OF 095/05. THE INTERACTION OF IRWIN AND A MID-TROPOSPHERIC LOW SOUTHWEST OF BAJA CALIFORNIA SHOULD RESULT IN A BRIEF TURN TOWARD THE EAST-NORTHEAST OR NORTHEAST WITH AN INCREASE IN FORWARD SPEED DURING THE NEXT DAY OR TWO. THE GUIDANCE THEN DEPICTS IRWIN BEING PULLED EASTWARD AND THEN SOUTHEASTWARD INTO A BROAD MONSOON-TYPE FLOW TO THE SOUTH OF MEXICO. AFTER BECOMING A REMNANT LOW...MOST OF THE GLOBAL MODELS TURN THE SYSTEM BACK TO THE WEST AS A LOW-LEVEL RIDGE BUILDS TO THE NORTH. THE OFFICIAL FORECAST HAS BEEN MODIFIED TO INDICATE THIS SCENARIO AND IS NEAR BUT GENERALLY A LITTLE FASTER THAN THE PREVIOUS ONE BETWEEN 24-72 HOURS...TO THE RIGHT OF THE MULTI-MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 14.9N 114.2W 40 KT 45 MPH 12H 12/0600Z 15.2N 113.1W 45 KT 50 MPH 24H 12/1800Z 16.1N 110.9W 50 KT 60 MPH 36H 13/0600Z 17.1N 108.9W 40 KT 45 MPH 48H 13/1800Z 17.3N 107.0W 35 KT 40 MPH 72H 14/1800Z 16.7N 104.5W 30 KT 35 MPH 96H 15/1800Z 16.0N 105.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 16/1800Z 15.5N 106.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER KIMBERLAIN NNNN
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Page last modified: Tuesday, 17-Jul-2012 13:44:20 UTC