WDPN32 PGTW 110900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 19W (CHANTHU) WARNING NR 
021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.1N 121.6E
   INITIAL INTENSITY: 140 KTS
   GEOGRAPHIC REFERENCE: 240 NM SOUTH OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 50 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) AND A 110505Z AMSR2
89GHZ MICROWAVE IMAGE STRONGLY SUGGEST STY 19W HAS COMPLETED AN
EYEWALL REPLACEMENT CYCLE (ERC) AND AT THE 0600Z HOUR, SHOWED SIGNS
OF A STRENGTHENING, WITH VORTICAL HOT TOWERS (VHT) RAPIDLY
ENCIRCLING A NASCENT AND WARMING EYE. SUBSEQUENT IMAGERY INDICATES
THE HAS ONCE AGAIN FILLED AND IS BECOMING INCREASINGLY RAGGED. THE
INITIAL POSITION AT 0600Z WAS ASSESSED WITH HIGH CONFIDENCE BASED
ON THE CONGRUENCE OF AGENCY FIX POSITIONS ON THE 10NM WIDE EYE, AND
EXTRAPOLATION OF THE MIC EYE FEATURE IN THE AFOREMENTIONED AMSR2
IMAGE. ANIMATED TAIWAN RADAR IMAGERY CONFIRMED THE POSITION, AS
WELL AS INDICATED THE CIRCULATION CENTER HAD SLOWED, AND THEN
TURNED SHARPLY NORTH-NORTHEASTWARD AROUND 0600Z. THE INITIAL
INTENSITY OF 140 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON
THE CURRENT INTENSITY ESTIMATES FROM MULTIPLE AGENCIES, BUT WELL
ABOVE THE SUBJECTIVE ADT AND SATCON ESTIMATES, PRIMARILY DUE TO THE
PRESENCE OF THE NASCENT EYE AND APPARENT INTENSIFICATION AT THE
SYNOPTIC TIME.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTH-SOUTH ORIENTED DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T7.5 - 155 KTS
   KNES: T7.0 - 140 KTS 
   CIMSS SATCON: 123 KTS AT 110130Z
   CIMSS ADT: 124 KTS AT 110540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: ENTRAINMENT OF MID-LEVEL DRY AIR ON THE EAST
SIDE, AND ABSORBTION OF 96W.

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: WHILE STY 19W APPEARS TO HAVE COMPLETED AN ERC
AND WOULD THUS BE EXPECTED TO BE ONCE AGAIN INTENSIFYING, RADAR
IMAGERY DEPICTS THE PRESENCE OF A VERY SMALL INNER EYE INSIDE OF A
MUCH LARGER SECONDARY EYEWALL. A 110740Z GMI 89GHZ MICROWAVE IMAGE
SHOWS THE OUTER EYEWALL IS FAIRLY RAGGED, AS WELL THE PRESENCE OF A
BAND OF DRY AIR WRAPPING INTO THE SYSTEM FROM THE EAST. THE
COMBINATION OF THESE FACTORS, ALONG WITH THE ABSORBTION OF THE
REMNANTS OF INVEST 96W, HAVE DISRUPTED THE CORE FROM RAPIDLY
REDEVELOPING. THOUGH STILL A SUPER TYPHOON, RECENT IMAGERY SUGGESTS
RAPID WEAKENING. RADAR IMAGERY SHOWS THE SYSTEM HAS TURNED SHARPLY
NORTHWARD, AS THE STEERING RIDGE HAS BECOME ORIENTED MORE
NORTH-SOUTH. THE SYSTEM IS FORECAST TO CONTINUE TRACKING NORTHWARD
ALONG THE WESTERN SIDE OF THE STR THROUGH TAU 48. THEREAFTER THE
STEERING PATTERN BECOMES HIGHLY COMPLEX, LEADING TO DRAMATIC
CHANGES IN FORECAST TRACK. BY TAU 48, A FAIRLY ROBUST STR IS
EXPECTED TO DEVELOP CENTERED TO THE SOUTHWEST OF BEIJING WITH
RIDGING EXTENDING EASTWARD ACROSS SOUTH KOREA AND INTO THE STR
SOUTHEAST OF JAPAN. THIS WILL LEAD TO A WEAK STEERING ENVIRONMENT,
IN WHICH STY 19W WILL BE TRAPPED BETWEEN THE TWO RIDGES. BETWEEN
TAU 48 AND 96, THE SYSTEM IS THUS EXPECTED TO REMAIN ROUGHLY
QUASI-STATIONARY OR DRIFT SLOWLY NORTH-NORTHEASTWARD AS IT REMAINS
FIRMLY ENSCONCED IN THE WEAK STEERING PATTERN. BY TAU 96, THE RIDGE
TO THE WEST IS EXPECTED TO WEAKEN AHEAD OF AN APPROACHING TROUGH,
WHILE THE EASTERN RIDGE STRENGTHENS AND MOVES WEST, ALLOWING FOR
STY 19W TO BREAKOUT AND BEGIN A TRACK TOWARDS THE EAST THROUGH TAU
120. THE PRESENCE OF PERSISTENT MID-LEVEL NORTHERLY SHEAR, AND
MID-LEVEL DRY AIR ENTRAINMENT SHOULD LIMIT ANY POTENTIAL FOR
NEAR-TERM INTENSIFICATION AND THE SYSTEM IS EXPECTED TO STEADILY
WEAKEN THROUGH THE ENTIRE FORECAST PERIOD. THE RATE OF
INTENSIFICATION SHOULD SLOW SLIGHTLY BETWEEN TAU 24 TO 48 AS VWS IS
FORECAST TO SLACKEN A BIT, BUT THE PACE OF WEAKENING WILL RESUME
THEREAFTER UNDER INCREASING SHEAR AND UPPER-LEVEL CONVERGENCE.   

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THOUGH TAU
48, AND HIGHLY UNCERTAIN THEREAFTER AS THE SYSTEM ENTERS THE WEEK
STEERING FLOW. MODEL SOLUTIONS SPREAD TO 83NM AT TAU 48. SPREAD IN
THE DETERMINISTIC MODELS ACTUALLY DECREASES AFTER TAU 48, BUT THIS
IS MISLEADING, AS ENSEMBLE SPREAD INCREASES DRAMATICALLY BOTH IN
TERMS OF DIRECTION AND SPEED, WITH POSSIBLE SOLUTIONS AT TAU 120
RANGING FROM DISSIPATION WEST OF SHANGHAI TO A STRONG TYPHOON OVER
SOUTHERN KYUSHU. AS THE BREAKPOINT IN FORECAST CONFIDENCE IS TAU
72, AND THE UNCERTAINTIES BEGIN TO MANIFEST THEMSELVES AT TAU 48,
THERE IS MEDIUM CONFIDENCE IN THE 0-72 TRACK FORECAST. IN THE
LONG-TERM, THERE IS LOW CONFIDENCE DUE TO THE UNCERTAINTIES IN THE
TIMING OF THE BREAKOUT FROM THE WEAK STEERING PATTERN. INTENSITY
GUIDANCE IS IN GOOD AGREEMENT ON THE STEADY WEAKENING SCENARIO,
WITH ONLY MINOR DEVIATIONS FROM THE MEAN. THE JTWC FORECAST LIES
ABOVE THE CONSENSUS MEAN BUT OTHERWISE TRACKS THE SLOPE OF THE
WEAKENING TREND WITH MEDIUM CONFIDENCE. 

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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