Tropical Storm MEGI Advisory Sun Sep 25

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (MEGI) WARNING
NR 06//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 20W (MEGI), LOCATED APPROXIMATELY 644 NM
SOUTHEAST OF KADENA AB, HAS TRACKED NORTHWESTWARD AT 13 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS
A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER WITH DEEP CONVECTIVE
BANDING WRAPPING INTO A FORMATIVE BUT RAGGED EYE. A 240709Z SSMIS
91GHZ IMAGE REVEALS THE BULK OF THE DEEP CONVECTIVE BANDING OVER THE
EASTERN SEMI-CIRCLE, HOWEVER, CONVECTIVE BANDING NOW WRAPS TIGHTLY
AROUND THE WESTERN SEMI-CIRCLE INTO A DEFINED CENTER. CONSEQUENTLY,
THERE IS GOOD CONFIDENCE IN THE CURRENT POSITION AND RECENT TRACK
MOTION. ADDITIONALLY, DVORAK INTENSITY ESTIMATES HAVE INCREASED AND
NOW RANGE FROM T3.5 TO T4.0 (55 TO 65 KNOTS) WITH A 240513Z SATCON
ESTIMATE OF 60 KNOTS. THE CURRENT INTENSITY IS ASSESSED AT 60 KNOTS
BASED ON AN AVERAGE OF THE DVORAK ESTIMATES. ANIMATED WATER VAPOR
IMAGERY REVEALS RADIAL OUTFLOW, ENHANCED BY A STRONG TUTT CELL TO
THE EAST. OVERALL, ENVIRONMENTAL CONDITIONS TO INCLUDE LOW VERTICAL
WIND SHEAR AND WARM SST ARE FAVORABLE FOR FURTHER DEVELOPMENT. TS
MEGI IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF THE DEEP
LAYERED SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
    A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
    B. TS 20W WILL CONTINUE TO TRACK WEST-NORTHWESTWARD IN A
STRAIGHT-RUNNER PATTERN THROUGH TAU 72 WHILE INTENSIFYING RAPIDLY
UNDER VERY FAVORABLE CONDITIONS. THE STR IS EXPECTED TO REMAIN
STRONG AND EAST-WEST ORIENTED THROUGH THE FORECAST PERIOD. AS A
RESULT, THE DYNAMIC GUIDANCE IS IN EXCELLENT AGREEMENT WITH A 75-NM
SPREAD IN SOLUTIONS AT TAU 72, JUST PRIOR TO LANDFALL ALONG THE
SOUTHEAST COAST OF TAIWAN. THE SYSTEM IS FORECAST TO PEAK AT 105
KNOTS BY TAU 48.
    C. AFTER TAU 72, TS MEGI WILL CROSS OVER SOUTHERN TAIWAN AND
WEAKEN SIGNIFICANTLY DUE TO LAND INTERACTION. AFTER RE-EMERGING OVER
THE TAIWAN STRAIT, THE SYSTEM WILL MAKE LANDFALL AGAIN OVER
SOUTHEAST CHINA NEAR TAU 96, AND WILL BEGIN DISSIPATING AS IT TRACKS
FURTHER INLAND. DUE TO THE TIGHT MODEL AGREEMENT IN THE EXTENDED
TAUS, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK, WHICH IS
PLACED CLOSE TO THE MULTI-MODEL CONSENSUS.//
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