Tropical Storm RAMMASUN Advisory Mon Jul 14

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (RAMMASUN) WARNING
NR 12//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 09W (RAMMASUN), LOCATED APPROXIMATELY 268 NM
NORTH-NORTHWEST OF YAP, HAS TRACKED WESTWARD AT 20 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS AN
UNCHANGED STRUCTURE WITH SUSTAINED CONVECTIVE BANDS ALONG THE
LEADING WESTERN EDGE OF THE SYSTEM AND HINTS AT A PARTIALLY EXPOSED
LOW LEVEL CIRCULATION CENTER (LLCC). A 130451Z AMSU-B MICROWAVE
IMAGE SHOWS DEEP CONVECTION HAS PERSISTED ALONG THE WESTERN PORTION
OF A POORLY DEFINED LLCC. UPPER LEVEL ANALYSIS REVEALS A CONTINUED
MARGINAL ENVIRONMENT CHARACTERIZED BY WEAKLY DIFFLUENT EASTERLY
OUTFLOW AND MODERATE (15 TO 20 KNOTS) VERTICAL WIND SHEAR (VWS).
THERE IS LOW CONFIDENCE IN THE CURRENT POSITION WHICH IS BASED UPON
THE AFOREMENTIONED SATELLITE IMAGERY ALONG WITH POSITIONAL FIXES
FROM PGTW AND RJTD THAT ARE 45NM SPREAD APART. THE INITIAL INTENSITY
IS BASED UPON THE UNCHANGED STRUCTURE AND CONGRUENT DVORAK INTENSITY
ESTIMATES FROM ALL AGENCIES. TS 09W IS QUICKLY TRACKING WEST ALONG
THE SOUTHERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) THAT IS
ANCHORED NORTH OF THE SYSTEM.
3. FORECAST REASONING.
   A. THE FORECAST TRACK SPEEDS HAVE BEEN INCREASED TO ACCOUNT FOR
THE PAST 12 HOUR TRACK SPEED INCREASES AND FORECAST INTENSITY HAS
BEEN DECREASED IN THE EARLY TERM DUE TO EARLIER THAN EXPECTED LAND
INTERACTION WITH LUZON.
   B. TS 09W IS FORECAST TO CONTINUE WESTWARD FOR THE NEXT 48 HOURS
ALONG THE SOUTHERN PERIPHERY OF THE ENTRENCHED STR. AFTER TAU 48, A
MID-LATITUDE TROUGH IS EXPECTED TO DIG ACROSS EASTERN CHINA, WHICH
WILL MODIFY THE STR LEADING TO A SLIGHT WEST-NORTHWESTWARD
DEFLECTION IN TRACK AS THE SYSTEM MAKES LANDFALL INTO CENTRAL LUZON.
THE CURRENT MARGINAL UPPER LEVEL ENVIRONMENT IS FORECAST TO PERSIST
FOR THE NEXT 48 HOURS WHICH WILL LEAD TO A LESS THAN CLIMATOLOGICAL
RATE OF INTENSIFICATION, THAT IS NOW EXPECTED TO JUST REACH TYPHOON
STRENGTH BEFORE MAKING LANDFALL. AFTER LANDFALL, THE ROUGH TERRAIN
WILL WEAKEN THE SYSTEM BEFORE IT RE-EMERGES IN THE SOUTH CHINA SEA
AS A MODERATE TROPICAL STORM AFTER TAU 72.
   C. IN THE EXTENDED TAUS, TS RAMMASUN IS EXPECTED TO CONTINUE TO
TRACK WEST-NORTHWESTWARD ACROSS THE SOUTH CHINA SEA AND TOWARDS
HAINAN ISLAND. WARM SEA SURFACE TEMPERATURES, DECREASED VWS, AND
INCREASED OUTFLOW WILL ALLOW FOR RE-INTENSIFICATION. MODEL GUIDANCE
IS IN GOOD AGREEMENT; HOWEVER, DUE TO THE LOW CONFIDENCE IN THE
INITIAL POSITION AND THE RECENT TRACK SPEED CHANGES, THE CONFIDENCE
IN THE FORECAST REMAINS LOW.//
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