Tropical Storm RAMMASUN Advisory Sat Jul 12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (RAMMASUN) WARNING
NR 09//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 09W (RAMMASUN), LOCATED APPROXIMATELY 187 NM
WEST OF ANDERSEN AFB, GUAM, HAS TRACKED WESTWARD AT 15 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
(EIR) REVEALS DEEPENING CENTRAL CONVECTION AS THE BROKEN FORMATIVE
BANDING ALONG THE LEADING WESTERN EDGE HAS BECOME MORE PERSISTENT
AND THE LOW LEVEL CIRCULATION CENTER (LLCC) IS BEGINNING TO
CONSOLIDATE. A 121205Z AMSU-B MICROWAVE IMAGE ADDITIONALLY SHOWS
IMPROVED LOW LEVEL STRUCTURE AS IMPROVED BANDING CAN BE OBSERVED
DESPITE AN OVERALL SMALL CONVECTIVE SIGNATURE. 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). THERE IS LOW CONFIDENCE IN THE INITIAL
POSITION DUE TO THE SOME AMBIGUITY IN THE EIR LOOP WHILE POSITION
FIXES FROM ALL REPORTING AGENCIES REMAIN WIDELY SPREAD. THE CURRENT
INTENSITY HAS BEEN INCREASED TO TROPICAL STORM STRENGTH (35 KNOTS)
BASED ON THE IMPROVED LOW LEVEL STRUCTURE OF THE SYSTEM SEEN IN THE
AFOREMENTIONED SATELLITE IMAGERY AND AS DVORAK INTENSITY ESTIMATES
FROM PGTW AND RJTD HAVE INCREASED TO 35 KNOTS AS WELL. 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 WILL BEGIN TO 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. AFTER LANDFALL, THE TERRAIN OF LUZON WILL
SIGNIFICANTLY WEAKEN THE SYSTEM AS IT MOVES INTO THE SOUTH CHINA
SEA. MODEL GUIDANCE IS IN GOOD AGREEMENT; HOWEVER, DUE TO THE LOW
CONFIDENCE IN THE INITIAL POSITIONING, THE OVERALL CONFIDENCE IN THE
FORECAST REMAINS LOW.//
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