000
WTPZ41 KNHC 120232
TCDEP1
 
TROPICAL STORM IRWIN DISCUSSION NUMBER  24
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP112011
800 PM PDT TUE OCT 11 2011
 
THE CONVECTIVE PATTERN OF IRWIN HAS CHANGED CONSIDERABLY DURING THE
LAST SEVERAL HOURS. AROUND 1800 UTC...A FAIRLY CIRCULAR AREA OF
CONVECTION EXISTED NEAR THE ESTIMATED LOW-LEVEL CENTER.  SINCE THAT
TIME...THE CONVECTION HAS BECOME MUCH MORE SPREAD OUT WITH THE MAIN
AREA IN A RAGGED-LOOKING CLUSTER TO THE NORTH OF THE CENTER. THE
INITIAL WIND SPEED IS HELD AT 40 KT...WHICH IS IN AGREEMENT WITH
THE DVORAK CI NUMBERS FROM TAFB AND SAB...AND ADT ESTIMATES FROM
UW-CIMSS.
 
IRWIN CONTINUES TO MOVE JUST SOUTH OF DUE EAST...AND THE INITIAL
MOTION ESTIMATE IS ABOUT THE SAME AS BEFORE...095/8. WATER VAPOR
IMAGERY INDICATES THAT THE ADVERTISED MID-LEVEL LOW IS BEGINNING TO
DEVELOP A FEW HUNDRED MILES TO THE SOUTHWEST OF THE BAJA PENINSULA.
THIS FEATURE IS EXPECTED TO CAUSE IRWIN TO TURN EAST-NORTHEASTWARD
WITH SOME INCREASE IN FORWARD SPEED DURING THE NEXT 36 TO 48 HOURS.
BEYOND THAT TIME...IRWIN IS FORECAST TO SLOW DOWN AND MAKE A
CLOCKWISE LOOP AS A LOW- TO MID-LEVEL RIDGE BUILDS TO THE NORTH OF
THE CYCLONE. THE OFFICIAL FORECAST IS SIMILAR TO THE PREVIOUS ONE
AND LIES NEAR THE MULTI-MODEL CONSENSUS.
 
THE ENVIRONMENT AHEAD OF IRWIN IS NOT FAVORABLE FOR STRENGTHENING.
THE INTERACTION WITH THE AFOREMENTIONED MID-LEVEL LOW AND THE
EXPECTED SIGNIFICANT INCREASE IN EASTERLY SHEAR BY THE END OF THE
FORECAST PERIOD SHOULD LIMIT THE STORM FROM INTENSIFYING MUCH...IF
AT ALL. THEREFORE...THE OFFICIAL FORECAST GENERALLY SHOWS LITTLE
CHANGE IN STRENGTH FOR THE NEXT 36 HOURS...FOLLOWED BY GRADUAL
WEAKENING. THIS FORECAST IS A LITTLE LOWER THAN THE PREVIOUS ONE
AND IS IN BEST AGREEMENT WITH THE LGEM GUIDANCE.

FORECAST POSITIONS AND MAX WINDS
 
INIT  12/0300Z 14.8N 113.3W   40 KT  45 MPH
 12H  12/1200Z 15.5N 111.8W   40 KT  45 MPH
 24H  13/0000Z 16.5N 109.8W   45 KT  50 MPH
 36H  13/1200Z 17.1N 107.9W   40 KT  45 MPH
 48H  14/0000Z 17.1N 106.2W   35 KT  40 MPH
 72H  15/0000Z 16.2N 104.2W   30 KT  35 MPH
 96H  16/0000Z 15.5N 105.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  17/0000Z 15.5N 107.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER CANGIALOSI