WDPN32 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (CHANTHU) WARNING NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.6N 125.0E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 260 NM EAST-NORTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT, SYMMETRIC SYSTEM THAT HAS STARTED TO MAKE ITS TURN TO THE
NORTHWEST OVER THE PAST SIX HOURS. A 091728Z AMSR2 89 GHZ PASS
SHOWS A WIDENING EYE FEATURE WITH CONVECTIVE BANDING FORMING IN THE
NORTHERN AND SOUTHERN PERIPHERIES. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE IN THE EIR LOOP THAT 
STACKED VERTICALLY DOWN TO THE LOW LEVEL CIRCULATION CENTER. THE 
INITIAL INTENSITY OF 120 KTS IS ASSESSED WITH MEDIUM CONFIDENCE 
BASED ON ANALYSIS OF AGENCY DVORAK ESTIMATES AND REFLECTS THE 
SUSTAINED EIR CONVECTIVE SIGNATURE. ANALYSIS INDICATED A FAVORABLE 
ENVIRONMENT WITH LOW VWS, STRONG RADIAL OUTFLOW AND VERY WARM SST. 
THE CYCLONE IS TRACKING WESTWARD ALONG THE SOUTHERN PERIPHERY OF THE 
STR TO THE NORTHEAST.

INITIAL WIND RADII BASIS: PERSISTENCE 

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


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 118 KTS AT 091321Z
   CIMSS ADT: 104 KTS AT 091430Z

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

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 19W HAS BEGUN TO TRACK TO THE NORTHWEST AS
IT MAKES ITS TURN AROUND THE STR TO THE NORTHEAST AND WILL CONTINUE
THIS TRACK AND KEEP ITS CURRENT INTENSITY THROUGH TAU 24. BY TAU
36, TY 19W WILL TURN TO THE NORTH AND REACH A MAX INTENSITY OF
125 KTS AS IT APPROACHES THE STR AXIS AND REMAIN IN A FAVORABLE
ENVIRONMENT WITH LOW VWS AND VERY WARM SSTS. BY TAU 48, TY 19W WILL
MAKE LANDFALL ON THE SOUTHERN COAST OF TAIWAN AND WILL BEGIN TO
DECREASE IN INTENSITY AS IT INTERACTS WITH THE CHUNG-YANG MOUNTAIN
RANGE. BY TAU 72, TY 19W WILL MOVE BACK OVER WATER OFF TAIWAN'S
NORTHERN COAST WITH A LOWERED INTENSITY OF 85 KTS AS A RESULT OF
LAND INTERACTION. IN ADDITION, THE SYSTEM WILL BEGIN TO TRACK
TOWARDS THE NORTH-NORTHEAST AS IT CONTINUES TO ROUND THE STR. BY
TAU 96, TY 19W WILL CONTINUE TO WEAKEN TO 75 KTS AS
IT ENTERS AN AREA OF HIGHER SHEAR BROUGHT ON BY THE PREVAILING
WESTERLIES. BY TAU 120, THE SYSTEM WILL BE UNDER THE INFLUENCE OF AN
UPPER LEVEL TROUGH APPROACHING FROM THE WEST THAT WILL TURN
ITS TRACK MORE TOWARDS THE NORTHEAST. TY 19W HAS UNDERGONE A SERIES
OF EYEWALL REPLACEMENT CYCLES (ERC) OVER THE PAST 72 HOURS. DUE TO
THE SMALL AND AGGRESSIVE NATURE OF THIS SYSTEM, THE LIKELIHOOD OF
MORE ERC EVENTS IS POSSIBLE WHICH MAY CAUSE A SLIGHT FLUCTUATION IN
INTENSITY ANALYSIS VALUES OVER THE NEXT 48 HOURS.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT IN REGARDS
TO THE RECURVATURE TRACK FORECAST SOLUTION. THE OVERALL MODEL
CONSENSUS ENVELOPE HAS BECOME TIGHTER LENDING TO HIGH CONFIDENCE IN
THE JTWC FORECAST TRACK THROUGH TAU 72. AFTER TAU 72, THE MODELS
SPREAD TO A MAX OF 180 NM WHICH IS NOT AS WIDE AS PREVIOUS
MODEL RUNS, HOWEVER THIS CONTINUED SPREAD LENDS ONLY MEDIUM 
CONFIDENCE 
FOR THE REMAINDER OF
THE FORECAST PERIOD. CONSENSUS INTENSITY GUIDANCE (ICNW) AGREEMENT 
HAS 
ALSO IMPROVED IN THE RECENT MODEL RUNS. THE JTWC
INTENSITY FORECAST IS HEDGED HIGHER THAN ICNW DUE TO THE SYSTEM
ENTERING A LOW VWS, HIGH OHC ENVIRONMENT AS IT ROUNDS THE RIDGE
AXIS, LENDING TO MEDIUM CONFIDENCE IN FORECAST INTENSITY DURING THE
FIRST 72 HOURS. AFTER TAU 72, THERE IS LOW CONFIDENCE IN
FORECAST INTENSITY DUE TO UNCERTAINTY IN THE DEGREE OF LAND 
INTERACTION 
WITH THE MOUNTAINOUS
THE SYSTEM WILL EXPERIENCE WITH THE TERRAIN OF TAIWAN.

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