Hurricane HELENE

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HURRICANE HELENE DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
1100 AM EDT SAT SEP 16 2006
 
GEOSTATIONARY SATELLITE IMAGERY INDICATES INCREASING ORGANIZATION OF
HELENE WITH ROBUST BANDING CONVECTION ON THE NORTH AND WEST
QUADRANTS...AND A RAGGED EYE ATTEMPTING TO FORM AS SEEN IN THE
VISIBLE IMAGERY.  MOREOVER...SSMI AND AMSU PASSES SHOW A NEARLY
COMPLETE EYEWALL.  BASED UPON CONSENSUS OF DVORAK ESTIMATES...THE
SYSTEM IS UPGRADED TO A 65 KT HURRICANE.  WHILE A SAHARAN AIR-LAYER
IS SEEN TO THE NORTH AND WEST OF HELENE IN CIMSS IMAGERY...TOTAL
PRECIPITABLE WATER ANALYSES FROM CIRA SUGGEST THAT THE DRY AIR
REMAINS AT LEAST A COUPLE HUNDRED MILES FROM THE CENTER OF THE
SYSTEM. CONTINUED SLOW INTENSIFICATION IS SUGGESTED OVER THE NEXT
THREE DAYS DUE TO 27.5 C SSTS...LIGHT/MODERATE VERTICAL SHEAR...AND
A MOIST ENVIRONMENT.  AT DAYS 4 AND 5...THE SSTS WARM UP...BUT
SHEAR INCREASES MAY MITIGATE FURTHER INTENSIFICATION.  A PLATEAUING
OF THE INTENSITY IS CALLED FOR AROUND 72 HRS WITH SLIGHT WEAKENING
THEREAFTER.  THE INTENSITY FORECAST IS A BLEND OF THE SHIPS...FSU
SUPER-ENSEMBLE...AND GFDL MODELS...WHICH IS SLIGHTLY WEAKER THAN
PREVIOUSLY PREDICTED AT THE LONG-LEADS.

CURRENT MOTION ESTIMATE IS 305/12.  HELENE IS ON THE SOUTHWEST SIDE
OF A DEEP-LAYER RIDGE AND IS HEADED TOWARD A BREAK IN THE RIDGE...
WHICH IS PARTIALLY BEING PRODUCED BY HURRICANE GORDON.  ALL
RELIABLE GUIDANCE IS IN CLOSE AGREEMENT WITH A CONTINUED MOVEMENT
ALONG THIS HEADING THROUGH 72 HR.  AT DAYS 4 AND 5...THERE IS A
SIGNIFICANT MODEL DIVERGENCE WITH THE UK...GFDL...ECMWF BEING
FASTER AND OFF TO THE NORTH AND THE GFS AND GFS ENSEMBLE SLOWER AND
OFF TO THE SOUTH.  THESE DIFFERENCES ARE BEING DRIVEN BY THE
AMPLITUDE OF THE SHORT-WAVE TROUGH THAT WILL BE PUSHING OFF OF THE
US EAST COAST AT THAT TIME.  THE NOGAPS AND CONSENSUS MODELS ARE IN
BETWEEN THESE POSSIBILITIES.  THE TRACK FORECAST IS CLOSE TO THE
CONSENSUS MODELS AND SLIGHTLY SLOWER AND TO THE RIGHT OF THE
PREVIOUS PREDICTION.
 
A G-IV AIRCRAFT RESEARCH MISSION IS CURRENTLY ENROUTE TO SAMPLE
HELENE'S ENVIRONMENT AS PART OF NOAA'S SALEX EXPERIMENT.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      16/1500Z 18.8N  45.6W    65 KT
 12HR VT     17/0000Z 19.5N  46.9W    70 KT
 24HR VT     17/1200Z 20.4N  48.3W    75 KT
 36HR VT     18/0000Z 21.1N  49.4W    80 KT
 48HR VT     18/1200Z 21.9N  50.6W    85 KT
 72HR VT     19/1200Z 23.5N  53.5W    90 KT
 96HR VT     20/1200Z 25.5N  56.5W    85 KT
120HR VT     21/1200Z 28.5N  58.0W    80 KT
 
$$
FORECASTER BEVEN/LANDSEA
 
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