Tropical Storm RAMMASUN Advisory Sun Jul 13

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 09W (NINE) WARNING
NR 08//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 09W (NINE), LOCATED APPROXIMATELY 99 NM
WEST OF ANDERSEN AFB, GUAM, HAS TRACKED WESTWARD AT 14 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
SHOWS THAT TD 09W HAS NOT IMPROVED IN STRUCTURE OVER THE PAST SIX
HOURS AS THE BROKEN FORMATIVE BANDING ALONG THE LEADING WESTERN EDGE
CONTINUES TO FLARE AS THE LOW LEVEL CIRCULATION CENTER (LLCC)
REMAINS POORLY DEFINED AND DIFFICULT TO LOCATE. A 120356 GMI 36GHZ
MICROWAVE CONCURS WITH THE MSI LOOP AS THE CONVECTION IS POORLY
ORGANIZED AROUND A SLOPPY LLCC. UPPER-LEVEL ANALYSIS REVEALS A
MODERATE 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
POOR ORGANIZATION OF THE LLCC SEEN IN THE MSI LOOP WHILE POSITION
FIXES FROM ALL AGENCIES REMAIN WIDELY SPREAD. THE CURRENT INTENSITY
REMAINS ASSESSED AT 30 KNOTS BASED ON THE POOR STRUCTURE OF THE
SYSTEM AND AS DVORAK INTENSITY ESTIMATES FROM PGTW AND RJTD REMAIN
AT 30 KNOTS. TD 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. TD 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, POSSIBLY REACHING
100 KNOTS BUT IS NOT REFLECTED IN THE FORECAST AS IT FALLS BETWEEN
TAU 96 AND TAU 120. AFTER LANDFALL, THE TERRAIN OF LUZON WILL
SIGNIFICANTLY WEAKEN THE SYSTEM AS 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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