Tropical Storm IRENE

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TROPICAL STORM IRENE DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 AM AST SUN AUG 21 2011
 
THE CLOUD PATTERN OF IRENE IS CHARACTERIZED BY WELL-DEFINED DEEP
CONVECTIVE BANDING FEATURES OVER THE NORTHERN SEMICIRCLE. THE STORM
STILL LACKS MUCH DEEP CONVECTION...OR STRONG WINDS...OVER THE
SOUTHERN PORTION OF THE CIRCULATION. AN AIR FORCE HURRICANE HUNTER
AIRCRAFT INVESTIGATING IRENE MEASURED PEAK 850 MB FLIGHT-LEVEL
WINDS OF 53 KT SO FAR...WHICH SUPPORTS KEEPING THE INTENSITY AT 45
KT FOR THIS ADVISORY. SINCE AN UPPER-LEVEL ANTICYCLONE IS
ESTABLISHED OVER THE TROPICAL CYCLONE AND THE SYSTEM WILL BE MOVING
OVER WARM WATERS...INTENSIFICATION SEEMS LIKELY AND IRENE IS
FORECAST TO BECOME A HURRICANE BY THE TIME IT REACHES HISPANIOLA.
AFTER THAT...THE INTENSITY FORECAST IS SUBJECT TO MORE THAN THE
USUAL LEVEL OF UNCERTAINTY...AS IT DEPENDS VERY MUCH ON HOW IRENE
WILL INTERACT WITH THE MOUNTAINOUS LAND MASSES OF HISPANIOLA AND
EASTERN CUBA OVER THE NEXT FEW DAYS. IF THE CENTER MOVES MORE OVER
THE WATER THAN INDICATED IN THE CURRENT FORECAST...IRENE WILL
LIKELY BECOME STRONGER THAN SHOWN HERE.

THE STORM IS BEING STEERED WEST-NORTHWESTWARD...285/17...BY THE FLOW
ON THE SOUTH SIDE OF A MID-LEVEL SUBTROPICAL RIDGE OVER THE WESTERN
ATLANTIC. 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 TOWARD THE NORTHWEST. THERE IS A
FAIR AMOUNT OF SPREAD IN THE TRACK GUIDANCE MODELS...ESPECIALLY AT
DAYS 4 TO 5. FOR EXAMPLE...THE GFDL MODEL TAKES IRENE TO THE WEST
OF THE FLORIDA PENINSULA WHILE THE HWRF MODEL TAKES IT THROUGH THE
NORTHWESTERN BAHAMAS. INTERESTS IN FLORIDA ARE ADVISED NOT TO FOCUS
ON THE EXACT FORECAST TRACK BECAUSE OF THE INHERENT UNCERTAINTIES
IN LONGER-RANGE FORECASTS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/1500Z 17.0N  63.2W   45 KT  50 MPH
 12H  22/0000Z 17.5N  65.5W   55 KT  65 MPH
 24H  22/1200Z 18.2N  68.2W   65 KT  75 MPH
 36H  23/0000Z 18.9N  70.9W   50 KT  60 MPH...INLAND
 48H  23/1200Z 19.6N  73.3W   45 KT  50 MPH...INLAND
 72H  24/1200Z 21.5N  76.5W   50 KT  60 MPH...OVER WATER
 96H  25/1200Z 24.0N  79.0W   65 KT  75 MPH
120H  26/1200Z 27.0N  81.5W   50 KT  60 MPH...INLAND
 
$$
FORECASTER PASCH
 
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