Tropical Storm CEMPAKA Advisory Tue Jul 20

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 10W (CEMPAKA) WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 21.7N 112.0E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 128 NM WEST-SOUTHWEST OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS SPIRAL
BANDS OF DEEP CONVECTION WRAPPING INTO AN OBSCURED LOW LEVEL
CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON ANALYSIS OF THE RAIN BANDS EVIDENT IN THE
COMPOSITE RADAR LOOP. THE INITIAL INTENSITY IS PLACED WITH MEDIUM
CONFIDENCE DUE TO THE SLIGHT SPREAD IN MULTI-AGENCY DVORAK CURRENT
INTENSITY ESTIMATES AND HIGHER INTENSITY ESTIMATE FROM THE
OBJECTIVE CIMSS ADVANCED DVORAK TECHNIQUE.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP LAYER STR
POSITIONED TO THE NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T4.5 - 77 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.5 - 77 KTS
   CIMSS ADT: 90 KTS AT 201240Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 MAKE LANDFALL ALONG THE COAST
OF CHINA IMMINENTLY. THEREAFTER, IT WILL BEGIN TO WEAKEN RAPIDLY
DUE TO INTERACTION WITH THE
UNDERLYING TERRAIN. AN INCOMING, MIDLATITUDE TROUGH WILL BEGIN TO
WEAKEN THE DOMINANT STEERING RIDGE AFTER THIS TIME AND THE WEAKENED
TY CEMPAKA WILL BEGIN A GENERALLY EQUATORWARD TRACK AS A RESULT
AFTER TAU 36 ALONG AN EXTENSION OF A RIDGE TO THE WEST. TY CEMPAKA
WILL THEN RENTER THE WARM WATERS OF THE SOUTH CHINA SEA BY TAU 48
AND GRADUALLY INTENSIFY. BEFORE TAU 72 IT WILL REACH 35 KTS AND
MAKE A SECOND LANDFALL OVER HAINAN. INTERACTION WITH THE TERRAIN
WILL ONCE AGAIN LEAD TO WEAKENING. AS THE SYSTEM REENTERS THE SOUTH
CHINA SEA FOR A SECOND TIME, IT WILL STRUGGLE TO INTENSIFY DUE TO
HIGH (GREATER THAN 25 KTS) VWS AND BEGIN DISSIPATING OVER WATER BY
TAU 120 AS A RESULT.
MODEL DISCUSSION: NUMERICAL MODEL TRACK AND INTENSITY GUIDANCE IS
IN TIGHT AGREEMENT THROUGH TAU 36, HOWEVER THEY DIVERGE THEREAFTER
DUE TO THE TIMING OF THE INTERACTION BETWEEN THE INCOMING
MIDLATITUDE TROUGH AND THE STEERING RIDGE. DESPITE THIS DIVERGENCE
IN MODEL TRACKS, ALL MEMBER OF THE JTWC MULTI-MODEL CONSENSUS AGREE
ON THE SOUTHWARD RECURVE SCENARIO WITH SUBSEQUENT RE-ENTRY INTO THE
SOUTH CHINA SEA AND FINAL EAST TO EAST-NORTHEASTWARD TRACK. THE
JTWC FORECAST TRACK IS PLACED ALONG THE MULT-MODEL CONSENSUS DUE TO
THE OVERALL AGREEMENT IN TRACK GUIDANCE.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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