Tropical Storm RAMMASUN Advisory Tue Jul 15

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (RAMMASUN) WARNING NR 19//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 09W (RAMMASUN), LOCATED APPROXIMATELY 289 NM
EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 13
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS TY 09W HAS MAINTAINED ITS DEGREE OF WRAP AND
CONVECTIVE DEPTH AS ITS 10-NM EYE, FILLED WITH THIN CIRRUS, HAS
RE-EMERGED. THE INITIAL POSITION IS BASED ON THE MSI ANIMATION WITH
HIGH CONFIDENCE. THE INITIAL INTENSITY IS BASED ON CONGRUENT DVORAK
ESTIMATES FROM PGTW, KNES, AND RJTD. UPPER LEVEL ANALYSIS REVEALS A
FAVORABLE ENVIRONMENT AS VIGOROUS EQUATORWARD AND WESTWARD OUTFLOW
CONTINUE WHILE VERTICAL WIND SHEAR ARE AT LOW (05 TO 10 KNOT) LEVELS.
TY 09W REMAINS ON A GENERALLY WESTWARD TRACK ALONG THE SOUTHERN
PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 09W IS FORECAST TO TRACK ON A MORE WEST-NORTHWESTWARD
TRAJECTORY AS A TRANSITORY MID-LATITUDE TROUGH DIGGING IN FROM
MONGOLIA WEAKENS THE STEERING STR. THE TYPHOON IS EXPECTED TO MAKE
LANDFALL JUST NORTH OF SORSOGON, PHILIPPINES, IN SIX HOURS.
AFTERWARDS, AS THE SYSTEM DRAGS ACROSS SOUTHERN LUZON AND INTO
MANILA, IT WILL WEAKEN DUE TO FRICTIONAL EFFECTS BUT WILL RE-EMERGE
IN THE SOUTH CHINA SEA (SCS) OVER SUBIC BAY SHORTLY AFTER TAU 30 AS A
STRONG TROPICAL STORM. WARM SST IN THE SCS PLUS CONTINUED FAVORABLE
UPPER LEVEL CONDITIONS WILL FAVOR RAPID RE-INTENSIFICATION, PEAKING
AT 90 KNOTS BY TAU 72.
   C. IN THE EXTENDED TAUS, TYPHOON RAMMASUN IS FORECAST TO CONTINUE
NORTHWESTWARD ACROSS THE SOUTH CHINA SEA MAKING A SECONDARY LANDFALL
OVER NORTHERN HAINAN NEAR TAU 84. IT WILL THEN CROSS THE GULF OF
TONKIN AND MAKE A FINAL LANDFALL OVER NORTHERN VIETNAM NEAR HANOI.
LAND INTERACTION WILL PRIMARILY CAUSE ITS WEAKENING; HOWEVER,
RAMMASUN WILL MAINTAIN A SOLID 80-KNOT TYPHOON INTENSITY BEFORE ITS
FINAL LANDFALL. DUE TO THE OVERALL GOOD AGREEMENT IN THE MODELS,
THERE IS HIGH CONFIDENCE IN THE FORECAST TRACK. HOWEVER, THERE IS
SOME UNCERTAINTY IN THE EXTENDED INTENSITY FORECAST WHICH IS
DEPENDENT ON THE EXTENT OF THE WEAKENING CAUSED BY LAND INTERACTION
IN THE INITIAL PORTION OF THE FORECAST.//
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