Monday, September 5, 2011

JTWC - Prognostic Reasoning for Tropical Cyclone Advisory 08 - Tropical Storm Noru

WDPN31 PGTW 050300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W WARNING NR 08//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
A. TROPICAL DEPRESSION (TD) 16W (NORU), LOCATED APPROXIMATELY
575 NM SOUTHEAST OF MISAWA, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD
AT 11 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY SHOWS THE LOW LEVEL CIRCULATION CENTER HAS BECOME
FULLY EXPOSED AND VIRTUALLY VOID OF CENTRAL CONVECTION. THE INITIAL
POSITION WAS BASED ON THE ABOVE ANIMATION WITH HIGH CONFIDENCE. THE
INITIAL INTENSITY WAS BASED ON DVORAK ESTIMATES FROM PGTW AND KNES.
UPPER LEVEL ANALYSIS INDICATES A TROPICAL UPPER TROPOSPHERIC TROUGH
CELL HAS MOVED OVER THE CYCLONE AND SNUFFED OUT OUTFLOW AND SHEARED
THE REMNANT CENTRAL CONVECTION TO THE NORTHWEST. THIS IS EVIDENT ON
ANIMATED WATER VAPOR IMAGERY. THE STORM MOTION HAS DECREASED AS THE
VERTICAL STRUCTURE WAS GREATLY REDUCED BUT REMAINS POLEWARD ALONG
THE WESTERN PERIPERY OF A HIGH-AMPLITUDE SUBTROPICAL RIDGE TO THE
EAST.
3. FORECAST REASONING.
A. THE INTENSITY FORECAST HAS SIGNIFICANTLY REDUCED TO REFLECT
THE RAPID EROSION OF THE CYCLONE AS DESCRIBED IN PARA 2.A. TRACK
FORECAST REMAINS THE SAME.
B. TD 16W IS EXPECTED TO CONTINUE TO DECAY AS IT TRACKS GENERALLY
NORTHWARD ALONG THE WESTERN PERIPHERY OF THE MID-LEVEL SUBTROPICAL
STEERING RIDGE THROUGHOUT THE FORECAST PERIOD. AS IT GAINS LATITUDE,
THE CYCLONE WILL DRIFT INTO THE BAROCLINIC ZONE AFTER TAU 12 AND
BECOME A COLD CORE LOW BY END OF FORECAST. CONCURRENTLY, SEA SURFACE
TEMPERATURES WILL DROP AND VERTICAL WIND SHEAR WILL INCREASE, HENCE,
THERE IS A DISTINCT POSSIBILITY THE SYSTEM WILL DISSIPATE OVER WATER
BEFORE TAU 24. THE AVAILABLE NUMERICAL GUIDANCE IS IN FAIR AGREEMENT
WITH A 20 DEGREE SPREAD AFTER TAU 24 WHERE GFDN IS TO THE LEFT AND
WBAR IS TO THE RIGHT OF THE MODEL ENVELOPE. THIS TRACK FORECAST IS
IN LINE WITH BUT SLIGHTLY FASTER THAN CONSENSUS.//

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