Tropical Storm MEGI Advisory Sat Sep 24

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (MEGI) WARNING
NR 02//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 20W (MEGI), LOCATED APPROXIMATELY 800 NM
SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTHWESTWARD AT
20 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS THE SYSTEM IS SLOWLY CONSOLIDATING, ALBEIT
FORMATIVE BANDS REMAIN FRAGMENTED. THE INITIAL POSITION IS BASED ON A
PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER EVIDENT IN THE MSI
LOOP AND LINES UP WITH A LOW REFLECTIVITY CIRCULATION FEATURE IN THE
222139Z SSMIS MICROWAVE IMAGE. THE INITIAL INTENSITY OF 35 KNOTS IS
BASED ON AN OVERALL ASSESSMENT OF AGENCY AND OBJECTIVE DVORAK
ESTIMATES AND REFLECTS THE SLIGHT INTENSIFICATION. THERE IS LOW
CONFIDENCE IN THE INITIAL POSITION GIVEN THE FORMATIVE NATURE OF THE
CYCLONE. UPPER LEVEL ANALYSIS INDICATES THE STORM IS IN THE VICINITY
OF AN ANTICYCLONIC POINT SOURCE WITH LOW VERTICAL WIND SHEAR AND
EXCELLENT DUAL OUTFLOW. ADDITIONALLY, SEA SURFACE TEMPERATURES AT 30C
ARE EXCEPTIONALLY WARM AND CONDUCIVE FOR FURTHER DEVELOPMENT. THE
CYCLONE IS TRACKING ALONG THE SOUTHWEST PERIPHERY OF A MID-LEVEL
REFLECTION OF THE SUBTROPICAL RIDGE (STR) TO THE NORTH-NORTHEAST.
3. FORECAST REASONING.
    A. THERE IS NO CHANGE TO FORECAST PHILOSOPHY FROM THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
    B. TS 20W IS EXPECTED TO CONTINUE ON A NORTHWESTWARD TRAJECTORY
THROUGHOUT ITS LIFESPAN, STEERED BY THE STR THAT IS FORECAST TO
BUILD. ENVIRONMENTAL CONDITIONS WILL REMAIN FAVORABLE FOR STEADY
INTENSIFICATION, REACHING A PEAK OF 100 KNOTS BY TAU 72 AS THE SYSTEM
DRIFTS ACROSS THE WARM PHILIPPINE SEA.
    C. IN THE EXTENDED PERIOD, TS MEGI WILL CROSS SOUTHERN TAIWAN AND
THE TAIWAN STRAIT PRIOR TO MAKING LANDFALL IN EASTERN CHINA BEFORE
TAU 120. LAND INTERACTION WILL BE THE PRIMARY CAUSE OF ITS RAPID
WEAKENING DURING THIS STAGE. MODEL GUIDANCE REMAINS IN GENERALLY GOOD
AGREEMENT, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST.//
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