[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 120852
TCDAT4
TROPICAL STORM IRENE DISCUSSION NUMBER  31
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT FRI AUG 12 2005

MICROWAVE IMAGERY FROM THE WINDSAT...DMSP...NOAA...AND TRMM
SATELLITES BETWEEN 2201Z AND 0335Z INDICATE THAT THE CENTER OF
IRENE IS A LITTLE TO THE NORTHEAST OF THE PREVIOUS ADVISORY
POSITION.  THE WINDSAT AND TRMM DATA SHOWED A WELL-DEFINED
LOW-LEVEL CENTER...AND CONVENTIONAL INFRARED IMAGERY SHOWS
INCREASING CONVECTIVE BANDING.  SATELLITE INTENSITY ESTIMATES ARE
55 KT FROM AFWA...AND 45 KT FROM TAFB AND SAB.  BASED ON THE
IMPROVED SATELLITE SIGNATURE...THE INITIAL INTENSITY IS INCREASED
TO 50 KT.

THE INITIAL MOTION IS NOW 310/13.  IRENE IS BETWEEN A DEEP-LAYER
RIDGE WITH A CENTER EAST OF BERMUDA AND AN UPPER-LEVEL LOW NEAR
26N74W.  A DEEP-LAYER WEAKNESS IN THE RIDGE EXISTS NEAR 32N70W DUE
TO A SHORT-WAVE TROUGH PASSING TO THE NORTH.  IRENE IS CURRENTLY
HEADING FOR THE WEAKNESS...WHICH THE LARGE-SCALE MODELS FORECAST TO
FILL OVER THE NEXT FIVE DAYS.  THE BIG QUESTION IS WILL IRENE
RECURVE THROUGH THE WEAKNESS BEFORE IT FILLS.  ALL DYNAMICAL MODEL
GUIDANCE SUGGESTS THE STORM WILL RECURVE BEFORE REACHING THE UNITED
STATES EXCEPT FOR THE OUTLIER GFDN...WHICH CALLS FOR A LANDFALL IN
NORTH CAROLINA.  THE OFFICIAL FORECAST COMPROMISES BETWEEN THESE
EXTREMES...CALLING FOR IRENE TO TURN NORTH-NORTHWESTWARD AFTER
48-72 HR AND MAINTAIN THAT MOTION THROUGH 120 HR.  THE FORECAST
TRACK CALLS FOR A SLIGHT LEFT TURN DURING THE FIRST 36-48 HR IN
ANTICIPATION OF RISING PRESSURES TO THE NORTH BEHIND THE SHORTWAVE
TROUGH.  OVERALL...THE FORECAST TRACK IS SHIFTED TO THE EAST OF THE
PREVIOUS TRACK....AND IS ALONG THE LEFT EDGE OF THE MAIN ENVELOPE
OF GUIDANCE.

IRENE HAS DEVELOPED GOOD ANTICYCLONIC OUTFLOW AND IS NOW IN A LIGHT
VERTICAL SHEAR ENVIRONMENT.  THUS...IT SHOULD STRENGTHEN AND BECOME
A HURRICANE IN 24-48 HR.  MID/UPPER LEVEL DRY AIR COULD STILL BE A
PROBLEM FOR DEVELOPMENT...AS COULD BE AN EDDY OF COOLER SEA SURFACE
TEMPERATURES ALONG THE FORECAST TRACK.  THE INTENSITY FORECAST
CALLS FOR IRENE TO REACH 75 KT IN 48 HR...THEN LEVEL OFF IN
INTENSITY AS IT PASSES OVER THE EDDY.  IRENE SHOULD MOVED OVER
WARMER SSTS AGAIN AFTER 72 HR...BUT HOW MUCH VERTICAL SHEAR MAY BE
PRESENT AT THAT TIME IS UNCERTAIN.  THUS...THE INTENSITY FORECAST
CALLS FOR NO CHANGE IN STRENGTH AFTER THAT TIME.

FIVE-DAY TROPICAL CYCLONE FORECASTS HAVE CONSIDERABLE UNCERTAINTY IN
BOTH LOCATION AND INTENSITY...SO IT IS STILL TOO EARLY TO TALK
ABOUT SPECIFIC THREATS TO THE EAST COAST OF THE UNITED STATES...
ESPECIALLY GIVEN THE CHANGES IN THE FORECAST TRACK.

FORECASTER BEVEN


FORECAST POSITIONS AND MAX WINDS

INITIAL      12/0900Z 27.6N  65.4W    50 KT
 12HR VT     12/1800Z 28.5N  66.7W    55 KT
 24HR VT     13/0600Z 29.4N  68.0W    65 KT
 36HR VT     13/1800Z 30.1N  69.1W    70 KT
 48HR VT     14/0600Z 31.0N  70.1W    75 KT
 72HR VT     15/0600Z 33.0N  71.5W    75 KT
 96HR VT     16/0600Z 34.5N  72.0W    75 KT
120HR VT     17/0600Z 36.0N  72.5W    75 KT


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