WDPN32 PGTW 100900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 19W (CHANTHU) WARNING NR 
017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.9N 123.4E
   INITIAL INTENSITY: 145 KTS
   GEOGRAPHIC REFERENCE: 445 NM SOUTH-SOUTHEAST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 54 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A DENSE,
COMPACT SYSTEM WITH A VERTICALLY STACKED 15NM DIAMETER EYE. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
AFOREMENTIONED EYE FEATURE. THE INITIAL INTENSITY OF 145 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON DVORAK AND ADT ESTIMATES
RANGING FROM T6.5-T7.5. THE CURRENT ENVIRONMENT IS MARGINALLY
FAVORABLE FOR SIGNIFICANT DEVELOPMENT GIVEN ITS DECREASING
PROXIMITY TO THE ROBUST OUTFLOW MECHANISM SITUATED TO ITS EAST.
DESPITE THIS, THE SEA SURFACE TEMPERATURES AND VERTICAL WIND SHEAR
(VWS) REMAIN FAVORABLE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE POSITIONED TO THE
NORTHEAST OF THE SYSTEM.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.5 - 155 KTS
   RJTD: T7.0 - 140 KTS 
   RCTP: T7.5 - 155 KTS
   KNES: T6.5 - 127 KTS
   CIMSS ADT: 143 KTS AT 100540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE DUAL-CHANNEL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: STY CHANTU HAS MAINTAINED ITS COMPACT
STRUCTURE WHILE COMPLETING ANOTHER INTENSIFICATION PERIOD UNDER
HIGHLY FAVORABLE CONDITIONS. HOWEVER, AS IT CONTINUES TO MOVE
NORTHWEST, IT IS EXPECTED TO LOSE THE RADIAL OUTFLOW THAT
ACCELERATED ITS DEVELOPMENT EARLIER. THEREFORE, SIGNIFICANT
INTENSIFICATION IS UNLIKELY WITHIN THE NEXT 24 HOURS DESPITE
SUSTAINED LOW VWS (15 KNOTS OR LESS) AND WARM SEA SURFACE
TEMPERATURES (29-30 DEGREES CELSIUS) IN THE LUZON STRAIT. LANDFALL
IN TAIWAN IS EXPECTED AROUND TAU 48. AFTER PASSING THROUGH TAIWAN,
INCREASING VWS WILL REDUCE STY 19W DOWN TO 55 KNOTS BY TAU 120.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL TIGHT AGREEMENT,
WITH CONSENSUS MOVING SLIGHTLY TO THE EAST OF TAIWAN, REDUCING LAND
INTERACTION EFFECTS. AFTER PASSING BY TAIWAN, TRACK GUIDANCE
SPREADS OUT TO 240NM BY TAU 72. THE FORECAST TRACK IS LAID SLIGHTLY
RIGHT OF THE MODEL CONSENSUS AT TAU 96 AND TAU 120 TO OFFSET THE
UNLIKELY ACUTE RECURVE SCENARIO EAST OF SHANGHAI, CHINA.
UNCERTAINTY IN THE JTWC INTENSITY FORECAST IS DUE TO THE COMPACT
NATURE OF THE SYSTEM AND THE VARIABILITY OF WEAKENING FROM LAND
PASSAGE.

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