Tropical Storm CEMPAKA Advisory Tue Jul 20

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 10W (CEMPAKA) WARNING NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 21.3N 112.4E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 117 NM WEST-SOUTHWEST OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 1 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM HAS
MAINTAINED OVERALL CONVECTIVE SIGNATURE AND A DEFINED, ALBEIT
CLOUD-FILLED EYE, AS IT TRACKED VERY SLOWLY TOWARD CHINA. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE
FEATURES BOTH IN THE MSI AND CNA COMPOSITE RADAR LOOPS THAT LINED
UP PERFECTLY WITH A MICROWAVE EYE IN THE 192317Z SSMIS 37GHZ IMAGE.
THE INITIAL INTENSITY OF 65 KTS IS ASSESSED WITH HIGH CONFIDENCE
BASED ON THE DVORAK ESTIMATES FROM PGTW AND KNES AND REFLECTS THE
SUSTAINED METSAT SIGNATURE.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T4.0 - 65 KTS
   RJTD: T3.5 - 55 KTS
   KNES: T4.5 - 77 KTS
   CIMSS ADT: 90 KTS AT 192340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: TY CEMPAKA WILL CONTINUE TO TRACK
NORTHWESTWARD UNDER THE STR AND MAKE LANDFALL SHORTLY AFTER TAU 12
ALONG THE SOUTHEASTERN CHINESE COAST NEAR YANGJIANG. AFTER TAU 36,
IT WILL BEGIN TO MAKE A TIGHT LEFT U-TURN TRACING THE WEST COAST OF
LEIZHOU PENINSULA INTO THE EASTERN TIP OF HAINAN BEFORE EXITING
BACK INTO THE SOUTH CHINA SEA (SCS) AFTER TAU 72. BY TAU 120, TY
10W WILL BE ACCELERATING NORTHEASTWARD IN THE MIDDLE OF THE SCS
BETWEEN HONG KONG AND LUZON, PHILIPPINES. LAND INTERACTION WITH THE
RUGGED CHINESE INTERIOR WILL RAPIDLY DECAY THE CYCLONE DOWN TO
30KTS. HOWEVER, AFTER TAU 48, INCREASED MOISTURE FROM THE GULF OF
TONKIN WILL REVIVE IT TO 35KTS, AND BY TAU 120 WILL BE UP TO 40KTS.
MODEL DISCUSSION: NUMERICAL MODELS ARE IN UNISON WITH THE TIGHT
U-TURN FORECAST TRACK, ALBEIT IN VARYING DEGREES AND SPEED WITH
NVGM OFFERING THE TIGHTEST TURN AND GFS AND JGSM ON THE WIDE MARGIN
OF THE ENVELOPE. THIS, PLUS GIVEN THE UNCERTAINTY OF LAND
INTERACTION AND THE ANTICIPATED STRONG SOUTHWESTERLY MONSOON SURGE
IN THE SCS, CONTRIBUTE TO AN OVERALL LOW CONFIDENCE IN THE JTWC
TRACK AND INTENSITY FORECASTS.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
NNNN
NNNN