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| #111424 (Received by flhurricane at: 4:34 PM 17.Sep.2006) TCDAT3 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 $$ |
