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Hurricane HELENE (Text)

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HURRICANE HELENE DISCUSSION NUMBER  22
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
500 PM EDT SUN SEP 17 2006
 
THERE HAS BEEN A DATA BONUS TODAY. A NOAA P-3 PLANE ON A RESEARCH
MISSION HAS MADE TWO FIXES ON HELENE AND JUST REPORTED A MINIMUM
PRESSURE OF 970 MB AND FLIGHT LEVEL WINDS OF 111 KNOTS AT 850 MB. A
DROPSONDE MEASURED A SURFACE WIND OF 90 KNOTS BUT THIS MIGHT NOT
REPRESENT A SUSTAINED VALUE. ALL OF THE ABOVE OBSERVATIONS
COINCIDES WITH T-NUMBERS OF 5.0 ON THE DVORAK SCALE ESTIMATED BY
ALL AGENCIES. I WAS TEMPTED TO LOWER THE INTENSITY A LITTLE BIT
SINCE THE SFMR ON BOARD OF NOAA PLANE HAS ONLY REPORTED PEAK WINDS
OF 80 KNOTS SO FAR.  HOWEVER...GIVEN THE CURRENT SATELLITE
PRESENTATION...THE 3-H AVERAGE OBJECTIVE NUMBERS AODT= 5.6 FROM
UW-CIMSS...AND THE DROP IN PRESSURE FROM THE 976 MB VALUE IN THE
PREVIOUS FIX...THE INITIAL INTENSITY IS KEPT AT 90 KNOTS AT THIS
TIME.  SOME ADDITIONAL STRENGTHENING IS POSSIBLE DURING THE NEXT
DAY OR TWO BEFORE THE SHEAR INCREASES AS SUGGESTED BY SHIPS MODEL.
THE OCEAN IS EXPECTED TO REMAIN WARM ALONG THE FORECAST TRACK. 

HELENE IS NOW MOVING TOWARD THE NORTHWEST OR 315 DEGREES AT 8 KNOTS
BETWEEN THE SUBTROPICAL RIDGE AND WEAKNESS LEFT BY HURRICANE
GORDON. HOWEVER...AS GORDON MOVES OUT THE RIDGE IS EXPECTED TO
BUILD WESTWARD AND THIS PATTERN COULD STEER HELENE TEMPORARILY ON A
MORE WESTWARD TRACK UNTIL A LARGE TROUGH BECOMES IN PLACE OVER THE
WESTERN ATLANTIC AND FORCES HELENE NORTHWARD. THE WESTWARD TURN FOR
THE NEXT 2 TO 3 DAYS IS SHOWN BY EVERY MODEL. THERE IS HIGH
UNCERTAINTY THEREAFTER SINCE GLOBAL MODELS HAVE BEEN SHIFTING THE
TRACK FROM ONE RUN TO THE NEXT. THE GFS HAS HAD THE LEFTMOST TRACK
SO FAR...BUT NOW THE UKMET MODEL HAS SHIFTED TO NEAR THE GFS
SOLUTION. THE GFDL HAS BEEN VERY CONSISTENT IN TURNING HELENE
NORTHWARD AND ITS SOLUTION IS HEAVILY WEIGHTED IN THE OFFICIAL
FORECAST.  
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      17/2100Z 21.2N  49.3W    90 KT
 12HR VT     18/0600Z 22.0N  50.3W    95 KT
 24HR VT     18/1800Z 22.8N  51.5W   100 KT
 36HR VT     19/0600Z 23.1N  53.0W   100 KT
 48HR VT     19/1800Z 23.5N  55.0W    95 KT
 72HR VT     20/1800Z 24.5N  57.5W    90 KT
 96HR VT     21/1800Z 27.1N  59.5W    85 KT
120HR VT     22/1800Z 30.5N  61.0W    80 KT
 
$$

FORECASTER AVILA
 
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