Tropical Storm IRWIN

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TROPICAL STORM IRWIN DISCUSSION NUMBER  15
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP112011
200 PM PDT SUN OCT 09 2011
  
IRWIN APPEARS TO BE SLIGHTLY BETTER ORGANIZED. THE CYCLONE HAS BEEN
MAINTAINING DEEP CONVECTION IN A BAND WRAPPING AROUND THE SOUTHERN
SEMICIRCLE FOR ALMOST 12 HOURS IN AN EASTERLY SHEAR ENVIRONMENT.
DVORAK T-NUMBERS HAVE INCREASED SOME...AND THE INITIAL INTENSITY IS
RAISED TO 45 KT IN ACCORDANCE WITH THE DVORAK ESTIMATE FROM TAFB.
 
SHROUDED BY ITS CONVECTIVE CLOUD CANOPY...THE CENTER OF IRWIN
CONTINUES TO BE DIFFICULT TO LOCATE IN CONVENTIONAL SATELLITE
IMAGERY. MICROWAVE FIXES SUGGEST THAT IRWIN IS MOVING 060/04...A
TAD TO THE RIGHT OF THE PREVIOUS ESTIMATE. EMBEDDED IN LOW- TO
MID-LEVEL WESTERLY FLOW...IRWIN IS EXPECTED TO MOVE GENERALLY
EAST-NORTHEASTWARD FOR THE NEXT DAY OR SO. THE INTERACTION OF IRWIN
WITH A MID-TROPOSPHERIC SHORTWAVE TROUGH CUTTING OFF INTO A LOW
SOUTHWEST OF BAJA CALIFORNIA SHOULD CAUSE THE TRACK TO BEND
EAST-SOUTHEAST AND THEN NORTHEAST AROUND THE LOW IN 36-72 HOURS.
THE NORTHWARD MIGRATION OF THE PACIFIC ITCZ ALONG WITH A CONTINUED
WESTERLY MID-LEVEL STEERING SHOULD GUIDE IRWIN ON AN EASTWARD OR
EVEN EAST-SOUTHEASTWARD COURSE LATER ON. THE TRACK GUIDANCE HAS
COME INTO MUCH BETTER AGREEMENT ON THIS SCENARIO THIS CYCLE. THE
OVERALL EASTWARD SHIFT IN THE GUIDANCE REQUIRES A SIZABLE
ADJUSTMENT TO THE PREVIOUS OFFICIAL FORECAST AT DAYS 4-5 BUT IS
STILL TO THE LEFT OF THE MULTI-MODEL CONSENSUS.
 
INTENSITY-WISE...IRWIN MAY HAVE SOME STRUGGLES AHEAD.  THE STORM
COULD BE TAPPING A MORE STABLE AIR MASS TO ITS NORTHWEST WHICH...IN
COMBINATION WITH PERSISTENT EASTERLY SHEAR...MAY DIMINISH ITS
CHANCE FOR INTENSIFICATION IN THE SHORT TERM. A PERSISTENCE OF
EASTERLY SHEAR AND THE POTENTIAL ADVERSE EFFECTS OF THE SST WAKE
ASSOCIATED WITH JOVA COULD BE NEGATIVE FACTORS FOR INTENSIFICATION
LATER IN THE FORECAST PERIOD.  THE STATISTICAL-DYNAMICAL GUIDANCE IS
BETTER AGREEMENT THAN BEFORE...BOTH SUGGESTING LITTLE CHANGE IN
INTENSITY FOLLOWED BY A SLOW DECAY. THE OFFICIAL FORECAST IS
SIMILAR TO THE PREVIOUS ONE AS IN GENERAL AGREEMENT WITH THE
INTENSITY CONSENSUS AIDS...ALBEIT SLIGHTLY LOWER AT DAYS 4-5.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  09/2100Z 15.2N 119.3W   45 KT  50 MPH
 12H  10/0600Z 15.7N 118.4W   45 KT  50 MPH
 24H  10/1800Z 15.8N 117.0W   40 KT  45 MPH
 36H  11/0600Z 15.6N 115.5W   40 KT  45 MPH
 48H  11/1800Z 15.4N 113.8W   40 KT  45 MPH
 72H  12/1800Z 16.0N 110.0W   40 KT  45 MPH
 96H  13/1800Z 17.5N 106.5W   40 KT  45 MPH
120H  14/1800Z 18.0N 105.0W   45 KT  50 MPH
 
$$
FORECASTER KIMBERLAIN
 
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