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Hurricane IGOR (Text)

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HURRICANE IGOR DISCUSSION NUMBER  26
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
1100 AM AST TUE SEP 14 2010

THERE HAS BEEN LITTLE CHANGE IN THE STRUCTURE OF IGOR DURING THE
PAST SEVERAL HOURS...WITH THE 20 NM WIDE EYE REMAINING WELL DEFINED
AND EYEWALL CONVECTIVE TOPS REMAINING COLDER THAN -70C.  SATELLITE
INTENSITY ESTIMATES ARE UNCHANGED FROM SIX HRS AGO...SO THE INITIAL
INTENSITY REMAINS 115 KT.  RECENT MICROWAVE OVERPASSES DO NOT YET
SHOW AN OUTER EYEWALL...BUT DO SHOW THAT A LARGE RAIN-FREE MOAT HAS
FORMED BETWEEN THE EYEWALL AND THE OUTER CONVECTIVE BANDS.  THE
CIRRUS OUTFLOW IS GOOD IN ALL DIRECTIONS.

THE INITIAL MOTION IS NOW 290/6.  IGOR IS MOVING TOWARD A WEAKNESS
IN THE SUBTROPICAL RIDGED CAUSED BY A BROAD DEEP-LAYER TROUGH OVER
THE NORTHEASTERN UNITED STATES AND THE NORTHWESTERN ATLANTIC.  THE
DYNAMICAL MODELS FORECAST THIS WEAKNESS TO PERSIST FOR THE NEXT
SEVERAL DAYS AS A SERIES OF SHORTWAVE TROUGHS MOVE THROUGH THE
BROADER TROUGH.  IN ADDITION...THE DYNAMICAL MODELS FORECAST AN
UPPER-LEVEL TROUGH TO DEVELOP NEAR THE SOUTHEASTERN COAST OF THE
UNITED STATES BY 96-120 HR...WITH A LARGE UPPER-LEVEL HIGH FORMING
OVER THE CENTRAL ATLANTIC.  THIS EVOLUTION SHOULD STEER IGOR
WEST-NORTHWESTWARD TO NORTHWESTWARD FOR THE NEXT 48-72 HR...
FOLLOWED BY A MORE NORTHWARD MOTION.  THE TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH THIS SCENARIO...ALTHOUGH THERE REMAINS SOME SPREAD
BETWEEN THE MORE WESTWARD UKMET/NOGAPS AND THE MORE EASTWARD GFDL. 
THE NEW FORECAST TRACK IS SHIFTED A LITTLE TO THE WEST OF THE
PREVIOUS TRACK AND LIES NEAR THE CENTER OF THE GUIDANCE ENVELOPE.

IGOR REMAINS IN AN ENVIRONMENT OF LIGHT VERTICAL WIND SHEAR AND WARM
SEA SURFACE TEMPERATURES...AND THESE CONDITIONS ARE FORECAST TO
PERSIST FOR THE NEXT 48-72 HR.  THUS...THE INTENSITY IS LIKELY TO
BE CONTROLLED BY HARD-TO-TIME EYEWALL REPLACEMENT CYCLES DURING
THIS TIME.  THE INTENSITY FORECAST CALLS FOR SOME INTENSIFICATION
BY 24 HR ON THE PREMISE THAT THE CURRENT INTERNAL CYCLE WILL BE
COMPLETE.  AFTER 72 HR...THE SEA SURFACE TEMPERATURES GRADUALLY
COOL ALONG THE FORECAST TRACK...AND SOUTHERLY UPPER-LEVEL WINDS
BETWEEN THE PREVIOUSLY MENTIONED TROUGH AND HIGH ARE EXPECTED TO
CAUSE INCREASED SHEAR.  THESE FACTORS SHOULD CAUSE IGOR TO
GRADUALLY WEAKEN...AND THE NEW INTENSITY FORECAST IS THE SAME AS
THE PREVIOUS FORECAST AT 96-120 HR.

INTERESTS IN BERMUDA SHOULD NOT FOCUS ON THE 5-DAY POINT...SINCE
TRACK ERRORS COULD EASILY BE A FEW HUNDRED MILES AT THAT FORECAST
INTERVAL.  IT IS STILL TOO EARLY TO SAY WITH CERTAINTY WHETHER IGOR
WILL HAVE A SIGNIFICANT IMPACT ON THAT ISLAND.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      14/1500Z 18.3N  52.3W   115 KT
 12HR VT     15/0000Z 18.8N  53.3W   115 KT
 24HR VT     15/1200Z 19.8N  54.8W   120 KT
 36HR VT     16/0000Z 20.8N  56.3W   120 KT
 48HR VT     16/1200Z 21.9N  57.8W   120 KT
 72HR VT     17/1200Z 24.5N  61.0W   115 KT
 96HR VT     18/1200Z 28.0N  64.0W   100 KT
120HR VT     19/1200Z 32.0N  65.5W    90 KT
 
$$
FORECASTER BEVEN
 
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