000
WTNT44 KNHC 210859
TCDAT4
 
TROPICAL STORM IRENE DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 AM AST SUN AUG 21 2011
 
SATELLITE IMAGES AND RADAR DATA FROM GUADELOUPE INDICATE THAT IRENE
HAS CHANGED LITTLE IN THE PAST 6 HOURS. THE CENTER REDEVELOPED
ABOUT 60 NMI FARTHER NORTH INTO THE DEEP CONVECTION. HOWEVER...A
NARROW WEDGE OF DRY AIR HAS BEEN ENTRAINED INTO THE NORTHERN AND
WESTERN QUADRANTS...WHICH HAS ERODED SOME OF THE INNER CORE
CONVECTION NEAR THE LOW-LEVEL CENTER. AS A RESULT...THE INITIAL
INTENSITY REMAINS AT 45 KT...WHICH IS SUPPORTED BY A SATELLITE
INTENSITY ESTIMATE OF T3.0/45 KT FROM TAFB. THE NEXT HURRICANE
HUNTER AIRCRAFT SCHEDULED TO RECONNOITER IRENE WILL BE 1200 UTC.
 
THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 280/18 DUE TO THE
UNCERTAINTY IN THE INITIAL POSITION. 00Z UPPER-AIR DATA FROM THE
NORTHERN CARIBBEAN ISLANDS AND BERMUDA INDICATE A FAIRLY STOUT
DEEP-LAYER SUBTROPICAL RIDGE EXISTS TO THE NORTH AND NORTHWEST OF
IRENE. THE RESULTANT MODERATE EASTERLY STEERING FLOW SHOULD KEEP
THE CYCLONE MOVING IN A GENERAL WESTWARD TO WEST-NORTHWESTWARD
DIRECTION FOR THE NEXT 72 HOURS OR SO. AFTER THAT...A WEAKNESS IN
THE RIDGE IS EXPECTED TO DEVELOP ACROSS THE EASTERN GULF OF
MEXICO...FLORIDA...AND THE EXTREME WESTERN ATLANTIC...WHICH SHOULD
ALLOW IRENE TO TURN NORTHWESTWARD ACROSS HAITI AND EASTERN CUBA AND
EMERGE OVER THE FLORIDA STRAITS IN ABOUT 96 HOURS. ALL OF THE
MODELS ARE IN EXCELLENT AGREEMENT ON THIS DEVELOPING TRACK SCENARIO
EXCEPT FOR THE UKMET AND GFDL MODELS. THOSE LATTER TWO MODELS KEEP
IRENE ON A WESTERLY TRACK SOUTH OF CUBA AND THROUGH THE YUCATAN
CHANNEL...DESPITE THEIR DEVELOPING A SIMILAR BREAK IN THE RIDGE
AXIS OVER FLORIDA BY DAYS 4 AND 5...AND ARE CONSIDERED OUTLIERS AT
THIS TIME. THE OFFICIAL FORECAST TRACK IS NORTH OF THE PREVIOUS
ADVISORY TRACK MAINLY DUE TO THE MORE NORTHWARD INITIAL POSITION...
AND LIES CLOSE TO THE CONSENSUS MODELS TVCN AND TVCA.

THE UPPER-LEVEL ENVIRONMENT IS EXPECTED TO BE QUITE FAVORABLE FOR
STRENGTHENING THROUGHOUT THE FORECAST PERIOD AS A RESULT OF LOW
SHEAR AND A MID-OCEANIC TROUGH TO THE EAST ACTING AS A MASS SINK
FOR THE OUTFLOW IN THE EASTERN SEMICIRCLE. HOWEVER...THE INTENSITY
FORECAST IS HEAVILY DEPENDENT ON HOW MUCH INTERACTION IRENE HAS
WITH THE MOUNTAINOUS TERRAIN OF HISPANIOLA AND WHAT THE INNER CORE
OF THE CYCLONE BECOMES AFTER IT EMERGES OFF THE NORTHEAST COAST OF
CUBA IN ABOUT 4 DAYS. ONCE OVER THE FLORIDA STRAITS...HOWEVER...
IRENE WILL HAVE AT LEAST 24 HOURS OVER SOME OF THE WARMEST WATER IN
THE ATLANTIC TO TAP INTO. THE OFFICIAL FORECAST REMAINS ON THE
CONSERVATIVE SIDE DUE TO LAND EFFECTS AND IS CLOSE TO A BLEND OF
SHIPS AND LGEM STATISTICAL INTENSITY MODELS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/0900Z 16.4N  61.3W   45 KT  50 MPH
 12H  21/1800Z 17.0N  63.7W   50 KT  60 MPH
 24H  22/0600Z 17.5N  66.7W   60 KT  70 MPH
 36H  22/1800Z 18.0N  69.2W   70 KT  80 MPH
 48H  23/0600Z 18.6N  71.5W   50 KT  60 MPH...INLAND
 72H  24/0600Z 20.3N  75.3W   50 KT  60 MPH...INLAND
 96H  25/0600Z 22.8N  78.2W   60 KT  70 MPH...OVER WATER
120H  26/0600Z 26.1N  80.7W   75 KT  85 MPH...INLAND
 
$$
FORECASTER STEWART