Tropical Depression IRWIN
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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
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