Tropical Depression IRWIN
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TROPICAL DEPRESSION IRWIN DISCUSSION NUMBER 28
NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011
800 PM PDT WED OCT 12 2011
SATELLITE IMAGES INDICATE THAT IRWIN HAS WEAKENED...AND THE CYCLONE
IS NOW NEARLY DEVOID OF DEEP CONVECTION. DVORAK CLASSIFICATIONS
SUPPORT LOWERING THE INITIAL WIND SPEED TO 30 KT...AND THIS MAKES
IRWIN A TROPICAL DEPRESSION ONCE AGAIN. GIVEN THE RECENT DECLINE IN
THUNDERSTORM ACTIVITY AND BECAUSE THE SHEAR IS NOT EXPECTED TO
LESSEN MUCH ON THURSDAY...IRWIN IS NOW FORECAST TO BECOME A REMNANT
LOW BY 36 HOURS...BUT THIS COULD OCCUR EVEN SOONER. SOME OF THE
MODELS SHOW IRWIN RESTRENGTHENING BY THE END OF THE FORECAST
PERIOD. THE OFFICIAL FORECAST...HOWEVER...KEEPS IRWIN AS A REMNANT
LOW BEYOND 36 HOURS DUE TO THE HIGH UNCERTAINTY AT THE LONGER TIME
RANGE.
IRWIN IS MOVING TO THE NORTHEAST AT ABOUT 13 KT ON THE EAST SIDE OF
A CUTOFF LOW. THE DEPRESSION IS EXPECTED TO TURN TO THE EAST AND
SLOW DOWN DURING THE NEXT 12 TO 24 HOURS STEERED BY THE LOW-LEVEL
WESTERLY FLOW. BEYOND THAT TIME...IRWIN...OR ITS REMNANT LOW...IS
EXPECTED TO MAKE A CLOCKWISE LOOP AS A LOW- TO MID-LEVEL RIDGE
BUILDS TO ITS NORTH. THE OFFICIAL FORECAST IS SIMILAR TO THE
PREVIOUS ONE AND IS CLOSEST TO THE ECMWF MODEL AND THE HFIP MODEL
CONSENSUS.
FORECAST POSITIONS AND MAX WINDS
INIT 13/0300Z 17.8N 108.6W 30 KT 35 MPH
12H 13/1200Z 18.2N 107.0W 30 KT 35 MPH
24H 14/0000Z 18.1N 105.3W 30 KT 35 MPH
36H 14/1200Z 17.4N 104.4W 30 KT 35 MPH...POST-TROP/REMNT LOW
48H 15/0000Z 16.7N 104.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 16/0000Z 16.0N 105.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 17/0000Z 16.0N 108.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 18/0000Z 16.0N 111.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
$$
FORECASTER CANGIALOSI
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