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Hurricane HELENE (Text)

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HURRICANE HELENE DISCUSSION NUMBER  30
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
ISSUED BY THE HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
500 PM EDT TUE SEP 19 2006
 
A NOAA AIRCRAFT MADE A COUPLE OF PASSES THROUGH HURRICANE HELENE
EARLY THIS AFTERNOON. THE ESTIMATED PRESSURE OF 960 MB THIS MORNING
APPEARED CORRECT AS THE PLANE MEASURED 958 MB BEFORE DEEPENING
ANOTHER 2 MB AN HOUR LATER. THE MAX FLIGHT LEVEL WIND WAS 98 KNOTS
AT 850 MB IN THE NORTHWEST QUADRANT AND TWO EYE WALLS WERE
PRESENT... 40NM AND 120NM OUT RESPECTIVELY. MICROWAVE SATELLITE
DATA ALSO INDICATED THESE TWO EYEWALL FEATURES THIS MORNING.
DESPITE THE PRESSURE LOWERING SLIGHTLY... THE 90 PERCENT REDUCTION
RULE CONCERNING MAX FLIGHT LEVEL WINDS SUGGESTS A 95 KNOT
HURRICANE. PLUS... THIS PRESENT EYEWALL CYCLE WOULD SUGGEST SLIGHT
FILLING OF THE CYCLONE AND THE WINDS LIKELY BROADENING THROUGHOUT
THE SYSTEM. OTHERWISE HELENE SHOWS TRUE SYMMETRY... A DEEP CENTRAL
DENSE OVERCAST AND A WELL-DEFINED EYE FEATURE ALL INDICATIVE OF A
MATURE HURRICANE UNDERGOING FLUCTUATIONS IN INTENSITY.

THE INITIAL MOTION IS 300 DEGREES AT 8 KTS AND THIS MOTION SHOULD
PERSIST INTO WEDNESDAY MORNING. THE TRACK FORECAST REMAINS VERY
CONSISTENT... A QUICK RECURVATURE TO THE NORTH... EVENTUALLY OFF TO
THE NORTHEAST AND PICKING UP FORWARD MOMENTUM. THE GLOBAL MODELS
AND OBJECTIVE AIDS SUGGEST THIS AS THE UPPER LOW AND AMPLIFIED
UPPER TROUGH UPSTREAM NEAR THE EAST COAST BREAKS DOWN THE
SUBTROPICAL RIDGE OVER THE CENTRAL ATLANTIC. HELENE SHOULD BEGIN
THIS NORTHWARD TREND DURING THE DAY ON WEDNESDAY AND BEFORE
REACHING 60W LONGITUDE. HPC GENERALLY FOLLOWED THE TIGHTLY
CLUSTERED OPERATIONAL RUNS OF THE GFS/GFDL AND UKMET ALONG WITH
DYNAMICAL GUIDANCE.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      19/2100Z 24.6N  54.1W    95 KT
 12HR VT     20/0600Z 25.2N  55.2W    95 KT
 24HR VT     20/1800Z 26.7N  56.5W   100 KT
 36HR VT     21/0600Z 28.9N  56.8W    95 KT
 48HR VT     21/1800Z 32.0N  56.3W    90 KT
 72HR VT     22/1800Z 39.0N  51.5W    90 KT
 96HR VT     23/1800Z 45.3N  41.0W    80 KT
120HR VT     24/1800Z 49.0N  30.5W    70 KT EXTRATROPICAL
 
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FORECASTER MUSHER
 
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