WDPN32 PGTW 070300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (CHANTHU) WARNING 
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.6N 136.6E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 818 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TS 19W HAS MAINTAINED A CENTRAL DENSE OVERCAST WITH A COMPACT CORE
OF INTENSE DEEP CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION
CENTER (LLCC) AS INDICATED IN ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY. DUE TO THE LACK OF RECENT MICROWAVE IMAGERY AND PARTIAL 
ASCAT IMAGERY, THERE IS MEDIUM CONFIDENCE IN THE INITIAL POSITION. 
THE INITIAL INTENSITY HAS BEEN CONSERVATIVELY INCREASED TO 50 KTS, 
HEDGED ABOVE THE PGTW DVORAK ESTIMATE, BASED ON THE CONSOLIDATING 
CONVECTIVE STRUCTURE. ALTHOUGH LIMITED IN EXTENT, THE SYSTEM HAS 
MAINTAINED RADIAL OUTFLOW AND LOW VERTICAL WIND SHEAR. WARM SEA 
SURFACE TEMPERATURES AND HIGH OCEAN HEAT CONTENT VALUES HAVE ALSO 
CONTRIBUTED TO THE RAPID CONSOLIDATION.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T4.0 - 65 KTS
   CIMSS ADT: 45 KTS AT 062340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: HIGH OCEAN HEAT CONTENT VALUES.

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 19W HAS CLEARLY CONSOLIDATED WITH STEADY 
IMPROVEMENT IN CONVECTIVE STRUCTURE. RAPID INTENSIFICATION AIDS HAVE 
TRIGGERED AGAIN BOLSTERING THE INCREASE IN THE FORECAST INTENSITIES 
THROUGH TAU 72. THE SYSTEM IS NOW EXPECTED TO INTENSIFY TO 90 KNOTS 
BY TAU 48 THEN 105 KNOTS BY TAU 72, A SLIGHTLY LESS THAN 
CLIMATOLOGICAL RATE. TS 19W SHOULD TURN WESTWARD THROUGH TAU 48 
UNDER THE STEERING INFLUENCE OF THE STR TO THE NORTH THEN MORE WEST-
NORTHWESTWARD AS IT TRACKS ALONG THE SOUTHWEST PERIPHERY OF THE STR 
THROUGH TAU 120. UPPER-LEVEL FLOW IS EXPECTED TO REMAIN ZONAL OVER 
THE EAST CHINA SEA WITH NO DEEP MIDLATITUDE SHORTWAVE TROUGHS 
EXPECTED TO WEAKEN THE SUBTROPICAL STEERING RIDGE OR BOOST POLEWARD 
OUTFLOW THUS THE INTENSIFICATION FORECAST IS CONSERVATIVE AT TAU 96 
(105 KNOTS) THEN WEAKENING AS THE SYSTEM INTERACTS WITH TAIWAN.

MODEL DISCUSSION: OVERALL CONFIDENCE IN THE JTWC TRACK FORECAST IS
MEDIUM WITH A 110NM SPREAD IN MODEL SOLUTIONS AT TAU 72 DIVERGING
TO 300NM BY TAU 120. NAVGEM, GFS AND THE GFS ENSEMBLE MEAN (AEMN) 
INDICATE A SHARPER, NORTH-NORTHWESTWARD TURN TOWARD NORTHERN TAIWAN 
AFTER TAU 96 BUT ARE CURRENTLY DISCOUNTED DUE TO THEIR HIGHLY 
INCONSISTENT FORECASTS RUN-TO-RUN AND, AS PREVIOUSLY MENTIONED, THE 
LACK OF A DEEP SHORTWAVE TROUGH TO BREAK THE STR DOWN. THUS THE JTWC 
FORECAST FAVORS A FLATTER TRACK TOWARD SOUTHERN TAIWAN THROUGH TAU 
120. INTENSITY GUIDANCE IS IN BETTER AGREEMENT WITH THE JTWC 
INTENSITY FORECAST SLIGHTLY HIGHER THAN THE INTENSITY CONSENSUS 
(ICNW) AND SLIGHTLY LOWER THAN HWRF, WHICH PEAKS THE INTENSITY AT 
115 KNOTS. THE LIKELIHOOD OF BINARY INTERACTION WITH TS 18W REMAINS 
VERY LOW AS THE TWO SYSTEMS CLOSE WITHIN 580-590NM AT TAU 60 TO TAU 
72, WHICH IS BORDERLINE AND UNLIKELY DUE TO THE COMPACT NATURE OF 
EACH SYSTEM.  

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