Tropical Storm RAMMASUN Advisory Paz, 13.07.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (RAMMASUN) WARNING
NR 10//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 09W (RAMMASUN), LOCATED APPROXIMATELY 257 NM WEST
OF ANDERSEN AFB, GUAM, HAS TRACKED WESTWARD AT 13 KNOTS OVER THE PAST
SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY REVEALS
DEEPENING CENTRAL CONVECTION REMAINS BROKEN AROUND THE LOW LEVEL
CIRCULATION CENTER (LLCC) AS DEVELOPMENT OF THE UPPER LEVEL OUTFLOW
CONTINUES TO STRUGGLE. THE CURRENT POSITION OF THE LLCC IS BASED ON A
POSITION FIX FROM PGTW AND A RECENT 121711Z GPM 36 GHZ MICROWAVE PASS
SHOWING WEAK LOW LEVEL BANDING. THE CURRENT INTENSITY HAS BEEN MAIN-
TAINED AT 35 KNOTS BASED UPON THE DVORAK ESTIMATE FROM PGTW, BUT KNES
AND RJTD WERE INDICATING A SLIGHTLY WEAKER SYSTEM AS THE CONVECTION
TEMPORARILY WEAKENED IN THE PAST SIX HOURS. UPPER-LEVEL ANALYSIS
REVEALS AN UNCHANGED, MARGINAL ENVIRONMENT CHARACTERIZED BY WEAKLY
DIFFLUENT EASTERLY OUTFLOW AND LOW TO MODERATE (10 TO 15 KNOTS)
VERTICAL WIND SHEAR (VWS). TS 09W CONTINUES TO TRACK ALONG THE
SOUTHERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) THAT IS
ANCHORED TO THE NORTH OF THE SYSTEM.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST TRACK PHILOSOPHY FROM THE
PREVIOUS PROGNOSTIC REASONING BULLETIN.
   B. TS 09W IS FORECAST TO TRACK WESTWARD FOR THE NEXT 72 HOURS
ALONG THE SOUTHERN PERIPHERY OF THE ENTRENCHED STR. ENVIRONMENTAL
CONDITIONS WILL REMAIN MARGINAL FOR THE NEXT 36 TO 48 HOURS, LEADING
TO A SLOW INTENSIFICATION PROCESS. NEAR TAU 72, VWS WILL BEGIN TO
DECREASE AND OUTFLOW IMPROVE, ALLOWING FOR INCREASED INTENSIFICATION
AS THE SYSTEM APPROACHES THE SOUTHWESTERN EDGE OF THE STR.
   C. AFTER TAU 72, A MID-LATITUDE TROUGH IS FORECAST TO DIG OVER
EASTERN CHINA, WHICH WILL MODIFY THE STR, LEADING TO A MORE WEST-
NORTHWEST TRACK TOWARDS LUZON. FAVORABLE SEA SURFACE TEMPERATURES IN
THE PHILIPPINE SEA ALONG WITH INCREASED OUTFLOW WILL LEAD TO A
MAXIMUM INTENSITY AS THE SYSTEM APPROACHES LAND, REACHING 95 KNOTS
BEFORE LANDFALL, WHICH IS CURRENTLY NOT REFLECTED IN THE FORECAST
DUE TO TIMING OF FORECAST POSITIONS AND THE TIMING OF LANDFALL WITH
LUZON. AFTER LANDFALL, THE TERRAIN OF LUZON WILL SIGNIFICANTLY
WEAKEN THE SYSTEM AS IT MOVES INTO THE SOUTH CHINA SEA. BETWEEN TAU
96 AND TAU 108 THERE WILL BE FURTHER WEAKENING TO AS LOW AS 65 KNOTS
BUT BY TAU 120 THE ENVIRONMENT, IN ASSOCIATION WITH MODEL GUIDANCE,
INDICATES A SLIGHT INCREASE IN THE INTENSITY OF THE SYSTEM TO 75
KNOTS. MODEL GUIDANCE IS IN GOOD AGREEMENT; HOWEVER, DUE TO THE LOW
CONFIDENCE IN THE UPPER LEVEL ENVIRONMENT, THE CONFIDENCE IN THE
FORECAST REMAINS LOW.//
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