WDPN32 PGTW 111500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (CHANTHU) WARNING NR 022//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.8N 121.8E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 199 NM SOUTH OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 48 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT AREA SYMMETRICAL DEEP CONVECTION SURROUNDING A RAGGED,
ELONGATED 10-NM WIDE EYE. AN 111029Z SSMIS 89GHZ MICROWAVE IMAGE
DEPICTED SPIRAL BANDING TO THE SOUTH, WRAPPING INTO A COMPACT LOW
LEVEL CIRCULATION CENTER (LLCC), WITH WEDGE OF DRIER AIR DEVOID OF
CONVECTION WRAPPING ACROSS THE NORTH TO THE WESTERN SIDE OF THE
CONVECTIVE CORE. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE 10-NM EYE AND RADAR DATA FROM TAIWAN. THE
INITIAL INTENSITY IS ASSESSED AT 120 KNOTS WITH MEDIUM CONFIDENCE,
HEDGED SLIGHTLY HIGHER THAN THE MAJORITY OF AGENCY CURRENT
INTENSITY ESTIMATES, AND ABOVE THE ADT ESTIMATE DUE TO THE PRESENCE
OF THE NASCENT EYE FEATURE, WHICH THE ADT IS NOT YET TRACKING.
SUBSEQUENT EIR IMAGERY SHOWS THE EYE CLEARING AND WARMING SLIGHTLY,
INDICATIVE OF ANOTHER ROUND OF SLIGHT INTENSIFICATION.

INITIAL WIND RADII BASIS: PERSISTENCE. OF NOTE, LATE RECEIPT OF A
111244Z ASCAT-B BULLSEYE PASS INDICATES THE INITIAL 111200Z BEST
TRACK WIND RADII WERE ROUGHLY 15 PERCENT TOO LARGE IN THE NORTHEAST
QUADRANT, ROUGHLY CORRECT IN THE SOUTHEAST QUADRANT AND
APPROXIMATELY 50 PERCENT TOO LARGE IN THE SOUTHWEST AND NORTHWEST
QUADRANTS. WIND RADII HAVE BEEN ADJUSTED FOR THE 1200Z WARNING.   

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE CENTERED
TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T7.0 - 140 KTS 
   KNES: T6.0 - 115 KTS
   CIMSS ADT: 107 KTS AT 111140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: SYSTEM IS MOVING OVER A TONGUE OF MODERATELY HIGH
OHC. 

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: TY 19W CONTINUES TO DEMONSTRATE A HIGH DEGREE
OF RESILIENCE, AND WHILE WEAKENING SIGNIFICANTLY SINCE THE PREVIOUS
ANALYSIS, IT STILL SHOWS SIGNS OF TRYING TO INTENSIFY. THE RAGGED
EYE SEEN AT 1200Z HAS BECOME BETTER ORGANIZED AND THE CORE
CONVECTION HAS BECOME MORE SYMMETRICAL IN THE SUBSEQUENT HOURS. THE
SYSTEM HAS FOUGHT OFF A BAND OF DRY AIR THAT WAS INTRUDING INTO THE
CORE, AND HAS PUSHED BACK AGAINST AND EARLIER BOUGHT OF NORTHERLY
SHEAR. THE SYSTEM IS MOVING ACROSS A TONGUE OF MODERATELY HIGH OHC
TO THE EAST OF LAN YU ISLAND, SUPPORTING THE IMPROVED 
REPRESENTATION IN THE EIR. TY 19W IS MOVING NORTH ALONG THE WESTERN
PERIPHERY OF A NORTH-SOUTH ORIENTED STR CENTERED SOUTHEAST OF
HONSHU AND IS EXPECTED TO MAINTAIN THIS TRACK THROUGH TAU 48. THE
SYSTEM MAY MOVE SLIGHTLY LEFT OF THE TRACK AS IT INTERACTS WITH AND
IS PULLED TOWARDS THE CENTRAL MOUNTAIN RANGE OF TAIWAN, BUT
OTHERWISE SHOULD SKIRT THE NORTHEAST TIP OF TAIWAN BEFORE
CONTINUING INTO THE EAST CHINA SEA. BY TAU 48 THE SYSTEM WILL MOVE
INTO A WEAK STEERING PATTERN, CAUGHT BETWEEN RIDGES CENTERED EAST
OF KYUSHU, WEST OF SHANDONG AND OVER SOUTHEASTERN CHINA. IT IS
EXPECTED THAT TY 19W WILL REMAIN QUASI-STATIONARY IN THE VICINITY
OF SHANGHAI WHILE REMAINING COCOONED IN THIS WEAK STEERING PATTERN
THOUGH AT LEAST TAU 96. BY TAU 120 THE RIDGE WESTERN RIDGE IS
EXPECTED TO ERODE AHEAD OF AN APPROACHING MID-LATITUDE TROUGH WHICH
WILL ALLOW THE SYSTEM TO START MOVING EASTWARD BY TAU 120. IN THE
NEAR TERM, TY 19W IS EXPECTED TO MAINTAIN ITS CURRENT INTENSITY AS
IT CONTINUES MOVING OVER THE HIGH OHC WATERS. HOWEVER, INCREASING
VWS AND INTERACTION WITH THE RUGGED TERRAIN OF TAIWAN WILL RESULT
IN STEADY WEAKENING AFTER TAU 24. ONCE THE SYSTEM SLOWS AND REMAINS
QUASI-STATIONARY NEAR SHANGHAI IT WILL RAPIDLY COME UNDER THE
INFLUENCE OF INCREASING SHEAR, COOLER SSTS, AND CONVERGENT FLOW
ALOFT, LEADING TO MORE RAPID WEAKENING THROUGH THE REMAINDER OF THE
FORECAST PERIOD. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT WITH A SPREAD
OF 80NM AT TAU 48. THEREAFTER THERE IS HIGH UNCERTAINTY AS THE
MODELS DEPICT A WIDE SPREAD OF POTENTIAL SOLUTIONS, AS WOULD BE
EXPECTED IN A WEAK STEERING PATTERN. HOWEVER, ALL MODELS AGREE ON
THE OVERALL SCENARIO OF A QUASI-STATIONARY PERIOD BETWEEN TAU 48
AND TAU 96, FOLLOWED BY AN ACCELERATION EASTWARD, DIFFERING ONLY ON
THE TIMING OF THE TURN AND ACCELERATION. HWRF REMAINS THE PRIMARY
OUTLIER, TAKING THE SYSTEM WELL INLAND WEST OF SHANGHAI AN THEN
ULTIMATELY INTO THE YELLOW SEA. ALL OTHER TRACKERS HOLD THE SYSTEM
OFFSHORE OR JUST ONSHORE IN THE VICINITY OF SHANGHAI DURING THE
QUASI-STATIONARY PERIOD. THE JTWC FORECAST REMAINS CONSISTENT WITH
THE PREVIOUS FORECAST AND THE CONSENSUS MEAN WITH MEDIUM CONFIDENCE
THROUGH TAU 72 AND LOW CONFIDENCE THEREAFTER. INTENSITY GUIDANCE
ALL SHOW STEADY TO RAPID WEAKENING FROM TAU 00. THE JTWC FORECAST
IS ABOVE ALL GUIDANCE EXCEPT THE TWRF THROUGH THE ENTIRE FORECAST,
THOUGH COAMPS-TC CONVERGES WITH THE FORECAST AT 50 KNOTS AT TAU
120. OVERALL INTENSITY FORECAST CONFIDENCE IS MEDIUM THROUGH TAU
72, AND LOW THEREAFTER.   

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