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HURRICANE HUMBERTO DISCUSSION NUMBER 15
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT MON SEP 24 2001
DATA FROM ANOTHER MULTI-AIRCRAFT RESEARCH MISSION IN SUPPORT OF THE
CONVECTION AND MOISTURE EXPERIMENT...CAMEX...INDICATE THAT HUMBERTO
IS STILL A MINIMAL HURRICANE. GPS DROPSONDES MEASURED SURFACE WIND
SPEEDS OF 64 AND 62 KNOTS. RADAR OBSERVATIONS FROM THE NOAA
AIRCRAFT...TRANSMITTED IN NEAR-REAL TIME TO THE NHC...INDICATE A
PARTIAL EYEWALL...OPEN OVER MOST OF THE SOUTHERN SEMICIRCLE.
ALTHOUGH VERTICAL SHEAR HAS NOT INCREASED GREATLY OVER HUMBERTO THUS
FAR...STRONGER UPPER-LEVEL WESTERLIES ARE IN ITS PATH. ALSO...THE
CYCLONE IS NEARING THE SHARP GRADIENT OF DECREASING SST.
THEREFORE...WEAKENING BELOW HURRICANE STRENGTH IS LIKELY TO OCCUR ON
TUESDAY...WITH CONTINUED WEAKENING EXPECTED OVER THE FORECAST
PERIOD. THE OFFICIAL FORECAST...LIKE THE PREVIOUS ONE...IS FOR
HUMBERTO TO BECOME EXTRATROPICAL BY 48 HOURS...AND SOON THEREAFTER
THE CYCLONE SHOULD BEGIN TO MERGE WITH A LARGE MID-LATITUDE LOW.
INITIAL MOTION HAS TURNED TOWARD THE NORTHEAST...040/12. THE
DOMINANT STEERING MECHANISM DURING THE FORECAST PERIOD SHOULD STILL
BE A LARGE DEEP-LAYER TROUGH OVER THE NORTHEASTERN UNITED STATES.
OBSERVATIONS FROM THE NOAA G-IV JET AIRCRAFT OF THE FLOW IN
HUMBERTO'S ENVIRONMENT INDICATE A SOMEWHAT MORE ZONAL STEERING FLOW
THAN PREVIOUSLY ESTIMATED. THIS...AND THE MORE EASTWARD INITIAL
MOTION...SUPPORTS SHIFTING THE OFFICIAL FORECAST MORE TO THE RIGHT
OF THE PREVIOUS TRACK. THIS IS IN GOOD AGREEMENT WITH THE LATEST
AVN AND FLORIDA STATE UNIVERSITY SUPERENSEMBLE GUIDANCE AS WELL.
FORECASTER PASCH
FORECAST POSITIONS AND MAX WINDS
INITIAL 25/0300Z 37.2N 63.9W 65 KTS
12HR VT 25/1200Z 38.5N 62.5W 60 KTS
24HR VT 26/0000Z 40.3N 60.2W 50 KTS
36HR VT 26/1200Z 41.5N 57.0W 45 KTS
48HR VT 27/0000Z 42.0N 53.0W 40 KTS...EXTRATROPICAL
72HR VT 28/0000Z 42.5N 43.5W 35 KTS...EXTRATROPICAL
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