Tropical Storm RAMMASUN Advisory Sat Jul 12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 09W (NINE) WARNING
NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 09W (NINE), LOCATED APPROXIMATELY 18 NM WEST-
NORTHWEST OF ANDERSEN AFB, GUAM, HAS TRACKED WEST-NORTHWESTWARD AT
11 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY SHOWS THAT THE DEEPEST CONVECTION LOCATED ALONG THE PERIPHERY
OF THE SYSTEM HAS STARTED TO DISSIPATE, BUT A NEW CENTRAL CONVECTIVE
MASS HAS DEVELOPED IN THE PAST FEW HOURS. RADAR IMAGERY FROM GUAM HAS
SHOWS THE LOW LEVEL CIRCULATION CENTER HAS UNDERGONE INCREASED
ORGANIZATIONAL IMPROVEMENTS OVER THE PAST SIX HOURS. THE CURRENT
INTENSITY HAS BEEN MAINTAINED AT 30 KNOTS, BASED ON DVORAK ESTIMATES
FROM PGTW, KNES AND RJTD HOLDING STEADY FROM THE PREVIOUS FORECAST.
TD 09W CONTINUES TO TRACK ALONG THE SOUTHERN PERIPHERY OF A DEEP-
LAYERED SUBTROPICAL RIDGE (STR), ANCHORED BETWEEN IWO TO AND GUAM.
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 STR. BASED ON THE SHIFT IN UPPER
LEVEL SUPPORT, THE OVERALL ENVIRONMENT WILL STRUGGLE TO ALIGN FOR THE
NEXT 36 TO 48 HOURS, LEADING TO A SLOW DEVELOPMENT POTENTIAL THROUGH
TAU 48. SEA SURFACE TEMPERATURES (SST) REMAIN FAVORABLE ALONG THE
FORECASTED TRACK, BUT THE OUTFLOW WILL REMAIN THE LIMITING FACTOR IN
THE NEAR TERM. BY TAU 72, VERTICAL WIND SHEAR IS EXPECTED TO DECREASE
ALLOWING FOR INCREASED INTENSIFICATION.
   C. AFTER TAU 72, A MID-LATITUDE TROUGH IS FORECAST TO DIG OVER
EASTERN CHINA, CAUSING A SHIFT IN THE STR, LEADING TO A MORE WEST-
NORTHWEST TRACK TOWARDS THE NORTHERN PART OF LUZON. ADDITIONALLY,
THE VERY FAVORABLE SST VALUES PRIOR TO THE APPROACH WILL LEAD TO
A MAXIMUM INTENSITY AROUND TAU 108, POSSIBLY NEAR 100 KNOTS BUT IS
NOT REFLECTED IN THE FORECAST AS THE TAU 120 INTENSITY OF 85 KNOTS
ENCOMPASSES A SLIGHT IMPACT TO THE LOW LEVEL STRUCTURE AS THE INFLOW
WITHIN THE NORTHWEST QUADRANT IS IMPACTED BY CROSSING OVER LUZON.
THE AVAILABLE MODEL GUIDANCE IS IN GOOD AGREEMENT; HOWEVER, DUE TO
THE INITIAL POSITIONING AND TRACK SPEED UNCERTAINTY, THE OVERALL
CONFIDENCE IN THE FORECAST REMAINS LOW.//
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