Tropical Storm IRENE

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TROPICAL STORM IRENE DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 PM AST SUN AUG 21 2011
 
IRENE IS GRADUALLY BECOMING BETTER ORGANIZED IN ITS APPEARANCE ON
SATELLITE IMAGES...WITH CURVED BANDS BECOMING BETTER DEFINED.  THE
CURRENT INTENSITY IS HELD AT 45 KT IN ACCORDANCE WITH OBSERVATIONS
EARLIER THIS AFTERNOON FROM THE AIR FORCE HURRICANE HUNTERS.
ANOTHER HURRICANE HUNTER PLANE IS SCHEDULED TO INVESTIGATE IRENE
AROUND 0000 UTC.  WITH A WELL-DEFINED UPPER-LEVEL OUTFLOW
ANTICYCLONE SITUATED OVER THE STORM...THE PRIMARY IMPEDIMENT TO
STRENGTHENING OVER THE NEXT COUPLE OF DAYS SHOULD BE LAND
INTERACTION.  IF IRENE MOVES OVER MORE OF HISPANIOLA OR OVER PARTS
OF EASTERN CUBA IT WILL LIKELY BE WEAKER THAN INDICATED
HERE...HOWEVER IF THE SYSTEM ENDS UP MOVING TO THE NORTH OF BOTH OF
THOSE LAND MASSES IT COULD STRENGTHEN MORE THAN EXPECTED.  THE
OFFICIAL INTENSITY FORECAST IS SOMEWHAT HIGHER THAN THE LATEST LGEM
STATISTICAL-DYNAMICAL GUIDANCE.
 
THE FORWARD MOTION HAS SLOWED A BIT AND IS NOW NEAR 285/15.  IRENE
CONTINUES TO BE STEERED BY THE FLOW ON THE SOUTH SIDE OF A
MID-LEVEL SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC.  THE
WEST-NORTHWESTWARD MOTION IS LIKELY TO CONTINUE FOR 1 TO 2 DAYS
WHICH WOULD BRING THE CENTER NEAR OR OVER PUERTO RICO...AND NEAR OR
OVER THE DOMINICAN REPUBLIC.  OVER THE NEXT FEW DAYS...A COUPLE OF
TROUGHS ARE FORECAST TO CREATE A WEAKNESS IN THE RIDGE NEAR THE
SOUTHEAST U.S. COAST WHICH SHOULD INDUCE A TURN TO THE RIGHT AROUND
DAY 3.  SEVERAL OF THE RELIABLE TRACK GUIDANCE MODELS SUCH AS THE
ECMWF AND GFS HAVE SHIFTED EASTWARD FROM THEIR PREVIOUS RUNS AND SO
HAS THE DYNAMICAL CONSENSUS.  THE OFFICIAL TRACK FORECAST HAS BEEN
SHIFTED A LITTLE TO THE RIGHT OF THAT FROM THE PREVIOUS ADVISORY
AND LIES ON THE WESTERN SIDE OF THE GUIDANCE ENVELOPE.  IT IS
IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK...ESPECIALLY AT
DAYS 4 TO 5 SINCE THE MOST RECENT 5-YEAR AVERAGE ERRORS AT THOSE
FORECAST TIMES ARE 200 AND 250 MILES RESPECTIVELY.
   
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/2100Z 17.7N  64.4W   45 KT  50 MPH
 12H  22/0600Z 18.2N  66.6W   60 KT  70 MPH...INLAND
 24H  22/1800Z 18.9N  69.3W   65 KT  75 MPH...INLAND
 36H  23/0600Z 19.6N  71.5W   50 KT  60 MPH...INLAND
 48H  23/1800Z 20.3N  73.5W   50 KT  60 MPH...OVER WATER
 72H  24/1800Z 22.7N  76.7W   60 KT  70 MPH
 96H  25/1800Z 25.5N  79.5W   75 KT  85 MPH
120H  26/1800Z 28.5N  81.5W   50 KT  60 MPH...INLAND
 
$$
FORECASTER PASCH
 
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