000
WTPZ41 KNHC 151446
TCDEP1
 
TROPICAL STORM IRWIN DISCUSSION NUMBER  38
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP112011
800 AM PDT SAT OCT 15 2011
 
THE AREA OF DEEP CONVECTION OVER THE SOUTHWESTERN PORTION OF THE
CIRCULATION HAS CONTINUED TO EXPAND SINCE THE PREVIOUS
ADVISORY...AND IRWIN HAS THE APPEARANCE OF A SHEARED TROPICAL
CYCLONE. ALTHOUGH DVORAK INTENSITY ESTIMATES SUPPORT A SLIGHTLY
LOWER WIND SPEED...THE INITIAL INTENSITY IS MAINTAINED AT 35 KT...
DUE TO THE RECENT INCREASE IN CONVECTION.  NEGATIVE ENVIRONMENT
CONDITIONS CONSISTING OF MODERATE NORTHEASTERLY SHEAR....DRY
MID-LEVEL AIR...AND COOLER WATERS OF THE WAKE OF JOVA...ARE LIKELY
TO CAUSE WEAKENING OF IRWIN IN THE SHORT-TERM.  LATER IN THE PERIOD
SOME OF THE INTENSITY GUIDANCE SUGGESTS RE-STRENGTHENING COULD
OCCUR...HOWEVER IRWIN IS STILL EXPECTED TO BE OVER ANOMALOUSLY COOL
WATERS AND VERTICAL SHEAR IS FORECAST TO INCREASE FURTHER.  AS A
RESULT...THE NHC INTENSITY FORECAST CONTINUES THE TREND SET BY THE
PREVIOUS ADVISORY AND SHOWS IRWIN BECOMING A TROPICAL DEPRESSION
VERY SOON AND DEGENERATING TO A REMNANT LOW WITHIN 72 HOURS.
 
IRWIN IS MOVING SOUTHWARD OR 185/6 KT.  THE CYCLONE IS FORECAST TO
TURN SOUTHWESTWARD THEN WESTWARD DURING THE NEXT COUPLE OF DAYS
AS A HIGH PRESSURE RIDGE BUILDS TO THE NORTH AND NORTHWEST OF THE
SYSTEM.  LATER IN THE PERIOD...THE STEERING CURRENT ARE EXPECTED TO
WEAKEN AND IRWIN IS FORECAST TO SLOW DOWN.  THE UPDATED FORECAST
TRACK IS SIMILAR TO THE PREVIOUS ADVISORY BUT SHOWS A SLIGHTLY
FASTER MOTION DURING THE NEXT 2 TO 3 DAYS.  THE NHC FORECAST...
HOWEVER...REMAINS SLOWER THAN THE GFS AND TVCE CONSENSUS IN
DEFERENCE TO THE MUCH SLOWER ECMWF SOLUTION.
   
FORECAST POSITIONS AND MAX WINDS
 
INIT  15/1500Z 16.5N 106.6W   35 KT  40 MPH
 12H  16/0000Z 15.8N 107.0W   30 KT  35 MPH
 24H  16/1200Z 14.9N 107.9W   30 KT  35 MPH
 36H  17/0000Z 14.7N 108.8W   30 KT  35 MPH
 48H  17/1200Z 14.7N 109.8W   30 KT  35 MPH
 72H  18/1200Z 14.7N 110.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  19/1200Z 14.7N 111.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  20/1200Z...DISSIPATED
 
$$
FORECASTER BROWN