Tropical Storm RAMMASUN Advisory Tue Jul 15

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (RAMMASUN) WARNING NR 21//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 09W (RAMMASUN), LOCATED APPROXIMATELY 152 NM EAST-
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD
AT 14 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY DEPICTS A WELL-STRUCTURED SYSTEM AS TY 09W
MOVES OVER LAND. THE CURRENT POSITION IS BASED ON A HIGH CONFIDENCE
SATELLITE EYE FIX ON A CLEAR, 20 NM DIAMETER EYE EVIDENT ON THE EIR
ANIMATION AND 150912Z SSMIS MICROWAVE IMAGERY. THE INITIAL INTENSITY
HAS INCREASED TO 110 KNOTS, SLIGHTLY LOWER THAN CONSISTENT DVORAK
ESTIMATES FROM PGTW, KNES, AND RJTD DUE TO THE CYCLONE BEING ON
LAND. UPPER-LEVEL ANALYSIS CONTINUE TO INDICATE
TY 09W REMAINS IN FAVORABLE ENVIRONMENT WITH LOW (05 TO 10 KNOT)
VERTICAL WIND SHEAR (VWS) AND EXCELLENT POLEWARD AND WESTWARD
OUTFLOW. TY 09W IS CURRENTLY TRACKING WEST-NORTHWESTWARD ALONG THE
SOUTHERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. THE INTENSITY FORECAST HAS BEEN INCREASED FOR EVERY POSITION
THROUGH TAU 72 DUE TO THE RAPID INTENSIFICATION OF A WELL-DEFINED
SYSTEM AND AN OVERALL INCREASE IN OBJECTIVE AID INTENSITY GUIDANCE.
   B. TY 09W IS FORECAST TO REMAIN ON WEST-NORTHWESTWARD TRACK OVER
THE NEXT 06 HOURS UNDER THE STEERING INFLUENCE OF THE STR. THE
TYPHOON WILL TURN SLIGHTLY MORE POLEWARD BY TAU 12 AS IT
ENCOUNTERS A WEAKNESS IN THE STR INDUCED BY A SHORTWAVE TROUGH
PASSING OVER EASTERN CHINA. TYPHOON RAMMASUN WILL WEAKEN
CONSIDERABLY AS IT TRACKS ACROSS SOUTHERN LUZON AND INTO MANILA OVER
THE NEXT 12 HOURS. HOWEVER, TY 09W IS EXPECTED TO REINTENSIFY AFTER
REEMERGING OVER THE SOUTH CHINA SEA (SCS) TO A CONTINUATION OF THE
AFOREMENTIONED FAVORABLE ENVIRONMENT. WARM SEA SURFACE TEMPERATURES
IN THE SCS AND CONTINUED FAVORABLE UPPER-LEVEL CONDITIONS WILL FAVOR
FURTHER RAPID RE-INTENSIFICATION, PEAKING AT 120 KNOTS PRIOR MAKING
LANDFALL OVER NORTHERN HAINAN ISLAND AROUND TAU 72.
   C. IN THE EXTENDED TAUS, THE SYSTEM WILL MAINTAIN A NORTHWESTWARD
TRAJECTORY AS IT CROSSES THE GULF OF TONKIN. LAND INTERACTION WILL
PRIMARILY CAUSE ITS WEAKENING; HOWEVER, TY 09W WILL MAINTAIN TYPHOON
STRENGTH AS IT MAKES THE FINAL LANDFALL INTO NORTHERN VIETNAM NEAR
HANOI. AVAILABLE MODEL GUIDANCE IS IN GOOD AGREEMENT WITH SOME
DIFFERENCES IN TRACK SPEED BUT IS OTHERWISE TIGHTLY GROUPED, LENDING
TO HIGH CONFIDENCE IN THE FORECAST TRACK. HOWEVER, THERE IS STILL
UNCERTAINTY IN THE INTENSITY FORECAST DUE TO THE EXTENT OF THE
WEAKENING ANTICIPATED WITH THE LAND INTERACTION, THEREFORE, THERE IS
OVERALL LOW CONFIDENCE IN THE JTWC FORECAST.//
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