Tropical Storm IRENE

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TROPICAL STORM IRENE DISCUSSION NUMBER  28
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT THU AUG 11 2005
 
DEEP CONVECTION HAS CONTINUED TO INCREASE WHILE BECOMING BETTER
ORGANIZED...EVEN THOUGH THE CLOUD PATTERN IS ELONGATED NORTHWEST TO
SOUTHEAST. LOW CLOUD LINES FEEDING INTO THE CYCLONE ALSO SUGGEST
THAT THE SURFACE CENTER MAY BE BROAD AND ELONGATED IN THE SAME
DIRECTION. DETERMINING THE CENTER LOCATION WAS WEIGHTED HEAVILY
TOWARD A TIGHT MID-LEVEL CIRCULATION NOTED IN 11/1052Z SSMI
MICROWAVE DATA. THE INTENSITY WAS INCREASED TO 45 KT BASED ON
SATELLITE ESTIMATES OF 45 KT FROM SAB AND AFWA...AND RECENT ODT
ESTIMATES OF T3.0/45 KT.
 
WHILE UNCERTAINTY REMAINS IN THE EXACT LOCATION OF THE SURFACE
CENTER...BUT MY BEST ESTIMATE OF THE INITIAL MOTION IS 300/15.
IRENE APPEARS TO BE MOVING FASTER THAN 15 KT...BUT SOME OF THAT
APPARENT MOTION MAY BE DUE TO RE-ORGANIZATION OF THE CENTER WITHIN
THE IMPROVING CONVECTIVE CLOUD MASS. THE LARGE-SCALE RIDGE PATTERN
HAS SHIFTED SLIGHTLY EASTWARD AND NORTHWARD OVER THE PAST 24 HOURS
WITH A HIGH CENTER LOCATED NEAR BERMUDA AND A RIDGE AXIS EXTENDING
SOUTHWESTWARD TO THE BAHAMAS. AS IRENE MOVES WEST-NORTHWESTWARD
INTO THE RIDGE...A GRADUAL DECREASE IN FORWARD SPEED IS EXPECTED.
THE NHC MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS SCENARIO
THROUGH 48 HOURS...AND THAT IS WHERE THE AGREEMENT ENDS. BY 72
HOURS...THE MODELS DIVERGE QUITE SIGNIFICANTLY WITH THE UKMET AND
NOGAPS RECURVING IRENE THROUGH THE RIDGE ALONG 70W...WHILE THE GFDL
AND GFDN ARE FARTHER WEST AND BRING IRENE VERY NEAR THE NORTH
CAROLINA COAST BY 120 HOURS. THE GFS...HOWEVER...QUICKLY DISSIPATES
IRENE AS IT HAS IN THE PAST 48 HOURS OF MODEL RUNS...AND KEEPS THE
RIDGE INTACT AND MOVES THE REMNANTS WEST-SOUTHWEST TOWARD FLORIDA
AND THE BAHAMAS. THE LATTER SOLUTION WAS DISCOUNTED GIVEN IRENE'S
CURRENT WELL ORGANIZED AND IMPROVING CONVECTIVE STRUCTURE. A
SHORTWAVE TROUGH CURRENTLY ALONG THE U.S. EAST COAST IS GRADUALLY
LIFTING OUT TO THE EAST-NORTHEAST...WHICH SHOULD ALLOW THE BERMUDA
MID-LEVEL RIDGE TO BUILD NORTH AND WESTWARD INTO THE CAROLINAS IN
THE SHORT TERM...WHICH SHOULD KEEP IRENE MOVING WEST-NORTHWESTWARD.
THE OFFICIAL FORECAST TRACK LEANS MORE TOWARD THE GFDL AND GFDN
SOLUTIONS...AND REMAINS CLOSE TO THE PREVIOUS FORECAST TRACK AND
THE LEFT SIDE OF THE MODEL GUIDANCE...GIVEN THAT THE UPSTREAM
SHORTWAVE TROUGH OVER THE CENTRAL U.S. IS RATHER WEAK AND
UNIMPRESSIVE AND MAY NOT WEAKEN THE RIDGE ALONG THE SOUTHEAST U.S.
COAST AS MUCH AS THE NOGAPS...UKMET...AND ECMWF MODELS SUGGEST.

SSTS ARE EXPECTED TO REMAIN BETWEEN 28.5C AND 29C...AND VERTICAL
SHEAR IS FORECAST BY THE SHIPS MODEL AND THE VARIOUS GLOBAL MODELS
TO REMAIN 10 KT OR LESS THROUGH 120 HOURS. SO THE ONLY INHIBITING
FACTOR AGAINST SIGNIFICANT INTENSIFICATION IS THE VERY DRY
MID-LEVEL AIR THAT IRENE WILL BE NAVIGATING THROUGH. THE OFFICIAL
INTENSITY FORECAST IS SIMILAR TO THE SHIPS MODEL THROUGH 72 HOURS
...AND THEN IS SLIGHTLY HIGHER AFTER THAT WHEN THE SHEAR IS
FORECAST TO DROP TO ABOUT 5 KT WHILE THE CYCLONE WILL BE MOVING
SLOWLY NORTHWARD NEAR THE WARMER GULFSTREAM.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      11/1500Z 25.1N  62.6W    45 KT
 12HR VT     12/0000Z 26.0N  64.4W    55 KT
 24HR VT     12/1200Z 27.2N  66.4W    60 KT
 36HR VT     13/0000Z 28.0N  68.0W    65 KT
 48HR VT     13/1200Z 28.6N  69.5W    70 KT
 72HR VT     14/1200Z 30.4N  72.3W    75 KT
 96HR VT     15/1200Z 32.5N  74.5W    75 KT
120HR VT     16/1200Z 35.0N  75.0W    75 KT

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