Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 15w (megi) Warning Nr 15//

From: SIU Weather Processor <[email-masked]>
Date: Sat, 16 Oct 2010 09:33:11 -0500

WDPN31 PGTW 161500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (MEGI) WARNING NR 15//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON 15W (MEGI), LOCATED APPROXIMATELY 580 NM EAST-
NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT
13 KNOTS OVER THE PAST SIX HOURS. MEGI HAS YET TO DEVELOP A WELL-
DEFINED EYE DESPITE A CURRENT INTENSITY OF 105 KNOTS. THIS INTENSITY
IS BASED ON A DATA-T AND CURRENT INTENSITY (CI) OF 5.5 FROM PGTW. A
CLOUD-FILLED EYE CAN BE EVIDENCED IN CERTAIN INFRARED ENHANCEMENTS,
WHICH HAS PROVIDED HIGH POSITION CONFIDENCE. AN UPPER LEVEL INVERTED
TROUGH OVER THE PHILIPPINE SEA HAS LIKELY STALLED RAPID
INTENSIFICATION BY LIMITING EXPANSION OF DEEP CONVECTION WITHIN THE
WESTERN SEMICIRCLE. POLEWARD OUTFLOW HAS IMPROVED AHEAD OF A
TRANSITORY MID-LATITUDE TROUGH AND EQUATORWARD OUTFLOW PERSISTS INTO
A TROPICAL UPPER LEVEL TROUGH CELL LOCATED NEAR 17N 152E. THE TRACK
HAS BEGUN TO FLATTEN TOWARDS THE WEST AS THE SUBTROPICAL STEERING
RIDGE STRENGTHENS IN THE WAKE OF A PASSING MID-LATITUDE TROUGH.
RISING 500 MB HEIGHTS OVER SOUTHEST ASIA CONFIRM A BUILDING MID-
LEVEL RIDGE.
3. FORECAST REASONING.
   A. THE FORECAST HAS BEEN SLOWED IN THE SOUTH CHINA SEA IN
RESPONSE TO THE MAJORITY OF THE CONSENSUS MEMBERS HINTING AT ANOTHER
PASSING TROUGH.
   B. MEGI IS STILL SLATED TO TRACK GENERALLY WESTWARD ALONG THE
SOUTHERN PERIPHERY OF THE DEEP LAYER STEERING RIDGE AND GLANCE LUZON
SHORTLY AFTER 18/00Z AROUND SUPER TYPHOON STRENGTH, ASSUMING THE
UPPER LEVEL TROUGH TO THE WEST FILLS. NOGAPS AND WBAR HAVE WALKED
TOWARDS THE MODEL CONSENSUS AND THE OFFICIAL JTWC FORECAST OVER THE
PAST 2 RUNS. NEARLY ALL THE TRACKERS INDICATE THE STEERING RIDGE
WILL STRENGTHEN OVER THE NEXT 3 DAYS, AND TRACK THE SYSTEM TOWARDS
THE WEST. THE SYSTEM WILL WEAKEN CONSIDERABLY OVER THE RUGGED
TERRAIN OF NORTHERN LUZON. IF IT TRACKS SOUTH OF TRACK, AS THE
LATEST ECMWF AND GFS RUNS SUGGEST, THEN MORE WEAKENING WILL OCCUR.
REGARDLESS, REINTENSIFICATION IS EXPECTED IN THE SOUTH CHINA SEA.
   C. AS STATED IN PARA 3.A. THE TRACK HAS SLOWED BEYOND TAU
72. NEARLY ALL THE MODEL TRACKERS ARE INDICATING A SLOW DOWN AROUND
THIS TIME, LIKELY IN RESPONSE TO ANOTHER PASSING TROUGH.//

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