Tropical Storm RAMMASUN Advisory Sun Jul 13

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (RAMMASUN) WARNING
NR 13//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 09W (RAMMASUN), LOCATED APPROXIMATELY 324 NM
NORTHWEST OF YAP, HAS TRACKED WESTWARD AT 20 KNOTS OVER THE PAST
SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR)
DEPICTS FLARING CONVECTIVE BANDING ALONG THE NORTHWESTERN EDGE OF A
LOOSELY WRAPPING LOW LEVEL CIRCULATION CENTER (LLCC) AS AN ISOLATED
BURST OF CENTRAL CONVECTION HAS DEVELOPED. A 131056Z SSMIS 91GHZ
MICROWAVE IMAGE SHOWS THE MID TO UPPER LEVEL TURNING ASSOCIATED WITH
THE SYSTEM HAS BECOME DISPLACED TO THE WEST OF THE LLCC THAT HAS
SLIGHTLY INCREASED IN DEFINITION OVER THE PAST FEW HOURS. UPPER
LEVEL ANALYSIS REVEALS A CONTINUED MARGINAL ENVIRONMENT
CHARACTERIZED BY 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. THE INITIAL
INTENSITY IS BASED UPON CONGRUENT DVORAK INTENSITY ESTIMATES FROM
ALL REPORTING 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. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 09W IS FORECAST TO CONTINUE WESTWARD FOR THE NEXT 36 TO 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 REACH MINIMAL
TYPHOON STRENGTH BEFORE MAKING LANDFALL INTO LUZON. AFTER LANDFALL,
THE ROUGH TERRAIN WILL WEAKEN THE SYSTEM BEFORE IT RE-EMERGES IN THE
SOUTH CHINA SEA AS A TROPICAL STORM.
   C. IN THE EXTENDED TAUS, TS RAMMASUN IS EXPECTED TO CONTINUE TO
TRACK WEST-NORTHWESTWARD ACROSS THE SOUTH CHINA SEA AND TOWARDS
NORTHERN HAINAN ISLAND, MAKING LANDFALL NEAR TAU 120 INTO THE
LUICHOW PENINSULA. WARM SEA SURFACE TEMPERATURES, DECREASED VWS, AND
INCREASED OUTFLOW IN THE SOUTH CHINA SEA WILL ALLOW FOR RE-
INTENSIFICATION REACHING 80 KNOTS PRIOR TO LANDFALL. MODEL GUIDANCE
IS IN GOOD AGREEMENT WITH SOME DIFFERENCES IN TRACK SPEED BUT IS
OTHERWISE TIGHTLY GROUPED. DUE TO THE LOW CONFIDENCE IN THE INITIAL
POSITION AND THE UNCERTAINTY IN THE TRANSLATIONAL SPEED, THE
CONFIDENCE IN THE FORECAST REMAINS LOW.//
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