WDPN32 PGTW 090300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 19W (CHANTHU) WARNING NR 
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.5N 128.1E
   INITIAL INTENSITY: 140 KTS
   GEOGRAPHIC REFERENCE: 415 NM EAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 48 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A COMPACT,
INTENSE, AND HIGHLY-SYMMETRICAL SYSTEM WITH A SHARPLY OUTLINED 5-NM
PINHOLE EYE, WHERE THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE. CONVECTIVE TOPS AROUND THE EYEWALL HAVE SLIGHTLY
DEEPENED AS EVIDENCED BY COOLER TEMPERATURES FROM 6HRS PRIOR. THE
INITIAL INTENSITY IS ALSO ASSIGNED WITH HIGH CONFIDENCE BASED ON
CONGRUENT AND CONCENTRIC AGENCY DVORAK FIXES AND REFLECTS THE SLIGHT 
6-HR INTENSIFICATION. ANALYSIS INDICATES CONTINUED FAVORABLE 
ENVIRONMENT WITH LOW VWS AND STRONG RADIAL OUTFLOW ALOFT, AND VERY 
WARM ALONG-TRACK SSTS OVER THE PHILIPPINE SEA. STY 19W IS TRACKING 
ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYERED STR TO THE NORTH.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T7.0 - 140 KTS 
   KNES: T7.0 - 140 KTS 
   CIMSS SATCON: 127 KTS AT 082202Z
   CIMSS ADT: 129 KTS AT 082340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

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: STY CHANTU WILL COMMENCE ON A RECURVATURE
TRACK PATTERN AS IT TURNS MORE WEST-NORTHWESTWARD THEN NORTHWESTWARD 
AFTER TAU 24 AS IT ROUNDS THE WESTERN EDGE OF THE STR. AFTER TAU 48, 
IT WILL CROSS TAIWAN AS IT TRACKS NORTHWARD AND CRESTS THE STR
AXIS BY TAU 72. AFTERWARD, THE SYSTEM WILL TURN MORE NORTH-
NORTHEASTWARD ON THE POLEWARD SIDE OF THE STR, BRUSH THE CHINESE 
COAST AND BY TAU 120 WILL BE JUST SOUTH OF SHANGHAI. THE FAVORABLE 
ENVIRONMENT WILL SUSTAIN THE CURRENT INTENSITY UP TO TAU 12; 
AFTERWARD, SLOWLY INCREASING VWS ASSOCIATED UPPER LEVEL CROSS
WINDS AND SOME LAND INTERACTION AS IT CLIPS THE NORTHEASTERN TIP OF
LUZON, WILL SLOWLY WEAKEN THE SYSTEM TO 125KTS BY TAU 48 AS IT
CROSSES THE LUZON STRAIT. AFTER TAU 48, A MORE DRASTIC EROSION WILL
OCCUR AS THE CYCLONE DRAGS ACROSS TAIWAN AND INTO HIGHER VWS, DOWN
TO 100KTS AS IT EXITS INTO THE TAIWAN STRAIT AROUND TAU 72. FURTHER
LAND INTERACTION, THIS TIME WITH THE CHINESE COAST, WILL FURTHER
WEAKEN THE SYSTEM MORE RAPIDLY DOWN TO 60KTS BY TAU 120 AS IT
APPROACHES SHANGHAI.   

MODEL DISCUSSION: NUMERICAL MODELS ARE NOW UNIFIED WITH A 
RECURVATURE TRACK FORECAST SOLUTION WITH A GRADUAL AND EVEN 
SPREADING TO 265NM BY TAU 120 WITH NVGM THE NOTABLE RIGHT-OF-TRACK 
OUTLIER ON THE RIGHT MARGIN OF THE ENVELOPE AND 105NM AWAY FROM THE 
MAIN CLUSTER AT TAU 120. IN VIEW OF THIS, THERE IS HIGH CONFIDENCE 
IN THE JTWC TRACK FORECAST UP TO TAU 72, AND MEDIUM CONFIDENCE 
AFTERWARD WHERE IT IS LAID JUST TO THE LEFT OF MODEL CONSENSUS TO 
OFFSET NVGM. THERE IS ALSO HIGH CONFIDENCE IN THE INTENSITY FORECAST 
UP TO TAU 72, WHERE IT IS HELD SLIGHTLY HIGHER THAN MODEL CONSENSUS 
TO BETTER REFLECT THE FAVORABLE ENVIRONMENT, AND MEDIUM CONFIDENCE 
AFTERWARD, IN VIEW OF THE UNCERTAIN IMPACTS THAT VWS AND LAND 
INTERACTIONS WILL BRING. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: HIGH
   INTENSITY 72-120 HR: MEDIUM//
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