[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 101436
TCDAT4
TROPICAL DEPRESSION IRENE DISCUSSION NUMBER  24
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT WED AUG 10 2005

THE CONVECTIVE CLOUD PATTERN THIS MORNING HAS IMPROVED SIGNIFICANTLY
COMPARED TO 24 HOURS AGO. IT IS STILL DIFFICULT...HOWEVER...TO
DETERMINE AN EXACT CENTER LCOATION...ESPECIALLY IN CONVENTIONAL
IMAGERY. THE INITIAL POSITION IS BASED ON CONTINUITY...A 24-HOUR
WESTWARD MOTION...AND TRMM AND MICROWAVE SATELLITE DATA. A 0912Z
QUIKSCAT PASS INTIMATED THAT A LOW-LEVEL CENTER COULD BE FARTHER
SOUTH NEAR 21N...BUT I PREFER TO REMAIN FARTHER NORTH NEAR THE
BETTER DEFINED MID-LEVEL CIRCULATION...WHICH ALSO ALLOWS FOR SOME
POSSIBLE REDEVELOPMENT FARTHER NORTH.

THE INITIAL MOTION ESTIMATE IS 275/10...EVEN THOUGH THE LONGER TERM
MOTION HAS BEEN 270/08. GLOBAL MODEL GUIDANCE HAS CONSISTENTLY
DISPLAYED A 20-30 DEGREE RIGHT-OF-TRACK BIAS THE PAST 48 HOURS.
THIS IS NOT SURPRISING SINCE THE MODELS HAVE KEPT IRENE WEAK OR
HAVE EVEN DISSIPATED IT...ALL THE WHILE MID-LEVEL NORTHERLY FLOW
HAS BEEN KEEPING THE CYCLONE FARTHER SOUTH ON A MORE WESTWARD
TRACK. WATER VAPOR IMAGERY AND SATELLITE-DERIVED WINDS FROM
UW-CIMSS STILL INDICATE A LARGE MID- TO UPPER-LEVEL ANTICYCLONE
LOCATED FROM THE SOUTHEASTERN U.S. EASTWARD ACROSS BERMUDA WITH
DEEP NORTH TO NORTHEASTERLY MID-LEVEL FLOW ON THE EAST SIDE
UNDERCUTTING THE IMPROVING UPPER-LEVEL OUTFLOW PATTERN. SO IN THE
SHORT TERM...A MORE WESTWARD COMPONENT OF MOTION IS PROBABLE...
BARRING ANY NORTHWARD REDEVELOPMENT OF THE LOW-LEVEL CENTER. BY
DAYS 4-5...MOST OF THE GLOBAL MODELS CREATE A WEAKNESS IN THE
SUBTROPICAL RIDGE OFF THE SOUTHEASTERN U.S. COAST...WITH A HIGH
CENTER SHIFTING EASTWARD TO NEAR BERMUDA. THIS IS EXPECTED TO ALLOW
IRENE TO MOVE SLOWLY NORTHWESTWARD AROUND THE SOUTHWEST PERIPHERY
OF THE HIGH. THE OFFICIAL FORECAST IS TO THE LEFT OF THE PREVIOUS
ADVISORY AND IS ON THE EXTREME LEFT...OR SOUTH ...SIDE OF THE NHC
MODEL GUIDANCE ENVELOPE. IF A WESTWARD MOTION CONTINUES TODAY AND
THE CENTER DOES NOT REFORM FARTHER NORTH...THEN THE TRACK WILL HAVE
TO BE SHIFTED EVEN MORE TO THE LEFT ON THE NEXT ADVISORY.

UPPER-LEVEL OUTFLOW HAS BECOME BETTER ESTABLISHED OVER THE PAST 12
HOURS AND IT IS EXPECTED TO CONTINUE TO IMPROVE FOR THE NEXT 3 DAYS
OR SO. HOWEVER...THE AFOREMENTIONED MID-LEVEL NORTHERLY FLOW
UNDERCUTTING THE OUTFLOW LAYER IS PRODUCING SOME MID-LEVEL SHEAR...
AS WELL AS ADVECTING VERY DRY AIR INTO THE SYSTEM. THE WARM
SEA-SURFACE TEMPERATURES AND IMPROVING OUTFLOW PATTERN SHOULD ALLOW
FOR AT LEAST SLOW INTENSIFICATION AS INTERMITTENT BURSTS OF DEEP
CONVECTION OCCUR NEAR THE CENTER. IT IS POSSIBLE THAT IRENE COULD
REACH HURRICANE STRENGTH BEFORE THE END OF THE FORECAST PERIOD.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      10/1500Z 22.4N  57.7W    30 KT
 12HR VT     11/0000Z 22.8N  59.4W    35 KT
 24HR VT     11/1200Z 23.7N  61.9W    40 KT
 36HR VT     12/0000Z 24.6N  64.3W    45 KT
 48HR VT     12/1200Z 25.7N  66.6W    50 KT
 72HR VT     13/1200Z 27.2N  69.3W    55 KT
 96HR VT     14/1200Z 28.5N  71.5W    60 KT
120HR VT     15/1200Z 31.5N  74.5W    60 KT

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