WDPN32 PGTW 101500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 19W (CHANTHU) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.7N 122.8E
   INITIAL INTENSITY: 140 KTS
   GEOGRAPHIC REFERENCE: 267 NM NORTH-NORTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 50 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 140 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON DVORAK AND ADT ESTIMATES
RANGING FROM T7.0-T7.5. THE CURRENT ENVIRONMENT IS MARGINALLY
FAVORABLE FOR SIGNIFICANT DEVELOPMENT GIVEN ITS INCREASING
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: PERSISTENCE

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.5 - 155 KTS
   RJTD: T7.5 - 155 KTS
   RCTP: T7.5 - 155 KTS
   KNES: T7.0 - 140 KTS 
   CIMSS SATCON: 137 KTS AT 100540Z
   CIMSS ADT: 152 KTS AT 101140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 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: STY CHANTU HAS MAINTAINED ITS COMPACT
STRUCTURE FOR THE LAST SIX HOURS. HOWEVER, AS IT CONTINUES TO MOVE
NORTHWEST, ITS EXPECTED TO CONTINUE DISTANCING ITSELF FROM ROBUST
OUTFLOW. 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 POSSIBLE BETWEEN TAU 36 UNTIL TAU 48 
AS IT SKIRTS ALONG ITS EASTERN COAST. AFTER PASSING TAIWAN, 
INCREASING VWS WILL REDUCE STY 19W DOWN TO 50 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 160NM BY TAU 72. INTENSITY AIDS SHOW SUSTAINED
WEAKENING THROUGH THE REMAINDER OF THE FORECAST. 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: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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