Tropical Storm IRWIN

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TROPICAL STORM IRWIN DISCUSSION NUMBER  37
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP112011
200 AM PDT SAT OCT 15 2011
 
CONVECTION HAS REDEVELOPED IN THE SOUTHEASTERN QUADRANT OF THE STORM
DURING THE PAST FEW HOURS.  HOWEVER THIS CONVECTION IS NOT AS
EXTENSIVE OR ORGANIZED AS YESTERDAY...AND DVORAK ESTIMATES ARE
DECREASING.  THE INITIAL WIND SPEED IS SET TO 35 KT WHICH MATCHES
THE CI NUMBERS FROM TAFB/SAB.  WATER VAPOR IMAGES SHOW DRY AIR
ALOFT POURING INTO THE CIRCULATION OF IRWIN...SO THE RECENT
CONVECTIVE BURST WILL PROBABLY BE SHORT-LIVED.  THIS DRY
AIR...COMBINED WITH THE CYCLONE SOON MOVING OVER THE COLD WAKE OF
JOVA AND AN INCREASE IN NORTHEASTERLY SHEAR... SHOULD CAUSE THE
SYSTEM TO WEAKEN INTO A TROPICAL DEPRESSION LATER TODAY.  ALMOST
ALL OF THE GUIDANCE BESIDES THE GFS NOW SHOW THIS SOLUTION...SO THE
OFFICIAL FORECAST IS LOWERED FROM THE PREVIOUS ONE.  SOME OF THE
GUIDANCE STILL SHOW SOME RESTRENGTHENING IN A COUPLE OF DAYS...BUT
THIS SEEMS UNLIKELY DUE TO THE FORECAST TRACK MOVING RIGHT OVER THE
WATERS UPWELLED FROM JOVA AND NORTHEASTERLY SHEAR ONLY LIKELY TO
GET STRONGER.  IRWIN IS FORECAST TO BECOME A REMNANT LOW BY DAY
3...AND I WOULD NOT BE SURPRISED IF IT HAPPENED SOONER.  

ALTHOUGH THE CENTER HAS BEEN A BIT DIFFICULT TO LOCATE...THE CYCLONE
APPEARS TO HAVE TURNED TOWARD THE SOUTH AT ABOUT 6 KT.  BUILDING
HIGH PRESSURE TO THE NORTHWEST OF IRWIN SHOULD CAUSE THE STORM TO
TURN TOWARD THE SOUTHWEST AND WEST OVER THE NEXT COUPLE OF DAYS. 
STEERING CURRENTS BECOME RATHER LIGHT AFTER THAT TIME...WITH THE
GLOBAL MODELS IN POOR AGREEMENT IN THE MEDIUM RANGE.  A COMPROMISE
IS TO SHOW LITTLE MOTION AFTER 48 HOURS...WHICH RESULTS IN THE NEW
FORECAST BEING BASICALLY AN UPDATE OF THE PREVIOUS ONE...ON THE
SLOW END OF THE GUIDANCE SUITE.  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  15/0900Z 17.2N 106.6W   35 KT  40 MPH
 12H  15/1800Z 16.3N 106.8W   30 KT  35 MPH
 24H  16/0600Z 15.3N 107.4W   30 KT  35 MPH
 36H  16/1800Z 14.7N 108.1W   30 KT  35 MPH
 48H  17/0600Z 14.7N 109.0W   30 KT  35 MPH
 72H  18/0600Z 15.0N 110.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  19/0600Z 15.0N 110.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  20/0600Z...DISSIPATED
 
$$
FORECASTER BLAKE
 
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