Advisories

WDPN32 PGTW 040900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (CHOI-WAN) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.9N 147.0E
   INITIAL INTENSITY: 125 KTS
   GEOGRAPHIC REFERENCE: 333 NM EAST-SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 42 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON 26W
(CHOI-WAN) WITH A HIGHLY SYMMETRIC AND COLD CENTRAL DENSE OVERCAST
SURROUNDING A 18 NM EYE. 26W HAS DISPLAYED AN IMPRESSIVE BOUT OF
RAPID DEVELOPMENT OVER THE PAST 12 HOURS, WITH AN INCREASE OF 25
KTS IN THE TIMEFRAME. THE EYE SIGNIFICANTLY WARMED STARTING AT
040200Z, TO A TEMPERATURE MEASURED AROUND 23 C AND HAS MAINTAINED
THAT PRESENTATION SINCE. A 040300Z AMSR3 89 GHZ MICROWAVE IMAGE
SHOWED A STRIKINGLY SYMMETRIC RING OF COLD BRIGHTNESS TEMPERATURES
OUTLINING THE EYEWALL. THE IMAGE ALSO SHOWED A SIZABLE GAP BETWEEN
THE INNER-CORE AND THE SURROUNDING RAINBANDS, HINTING AT THE
PRESENCE A POTENTIAL DRY SLOT. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE WELL-DEFINED EYE IN ANIMATED MSI
AND THE AMSR3 IMAGE. THE INITIAL INTENSITY OF 125 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMSS
INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: THE WESTERN PERIPHERY OS A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.5 - 127 KTS
   CIMSS SATCON: 131 KTS AT 040540Z
   CIMSS ADT: 115 KTS AT 040540Z
   CIMSS AIDT: 112 KTS AT 040540Z
   CIMSS D-MINT: 127 KTS AT 040335Z
   CIMSS D-PRINT: 135 KTS AT 040540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG DUAL-CHANNEL

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 26W IS FORECAST TO TRACK GENERALLY
NORTHWARD ALONG THE WESTERN PERIPHERY OF THE STR TO THE EAST
THROUGH TAU 48. NEAR TAU 48, 26W WILL APPROACH THE STEERING RIDGE
AXIS AND BEGIN TO TURN NORTHEASTWARD AS IT TRAVERSES THE
NORTHWESTERN EXTENT OF THE STR. TRACK SPEEDS WILL SIGNIFICANTLY
INCREASE STARTING AT TAU 60, ONCE 26W GETS PICKED UP BY A
MIDLATITUDE TROUGH AND INTERACTS WITH THE STRONG UPPER-LEVEL FLOW.
EXTRATROPICAL TRANSITION (ETT) IS FORECAST TO BEGIN AT TAU 60 AND
COMPLETE NEAR TAU 72, ONCE 26W BECOMES EMBEDDED UNDERNEATH THE JET
SOUTH OF THE KAMCHATKA PENINSULA. IN TERMS OF INTENSITY, 26W IS
FORECAST TO PEAK NEAR TAU 12 WITH AN INTENSITY OF 130 KTS, THOUGH
IT COULD BE EVEN HIGHER IF THE SYSTEM DOES NOT UNDERGO AN EYEWALL
REPLACEMENT CYCLE (ERC) UNTIL THEN. THE MICROWAVE-BASED PROBABILITY
OF EYEWALL REPLACEMENT CYCLE (MPERC) OUTPUT BY CIMSS IS 42 PERCENT
AS OF 040600Z. AFTER TAU 12, 26W IS FORECAST TO BEGIN GRADUALLY
WEAKENING DUE TO LOWERING OCEAN HEAT CONTENT AND DRY AIR INTRUSION
FROM THE WEST. AT TAU 48, 26W WILL APPROACH THE 26 C SST ISOTHERM
AND WESTERLY VERTICAL WIND SHEAR WILL BEGIN TO INCREASE, FURTHER
AIDING IN WEAKENING THE SYSTEM. BY TAU 78, WESTERLY SHEAR WILL
INCREASE TO OVER 70 KTS AS THE SYSTEM TRANSITIONS INTO A COLD-CORE
LOW. NOTABLY, 26W WILL TAP INTO AN EXTREME POLEWARD OUTFLOW CHANNEL
LEADING UP TO THE COMPLETION OF ETT, SUPPORTED BY A STRONG JET
MAXIMUM TO THE NORTH. AS A RESULT, 26W IS EXPECTED TO MAINTAIN
TYPHOON INTENSITY THROUGH THE TRANSITION.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT
THROUGHOUT THE FORECAST PERIOD WITH A CROSS-TRACK SPREAD AT TAU 72
MEASURED TO BE JUST 90 NM. MOST OF THE UNCERTAINTY IN THE TRACK
STEMS FROM THE SPEED OF ADVANCE FROM TAU 60 TO 72. THE ALONG-TRACK
SPREAD AT TAU 72 IS ABOUT 290 NM WITH GFS CONTINUING TO BE THE
SLOWEST TRACKER AND THE EC-AIFS AS THE FASTEST. THE JTWC TRACK
FORECAST IS PLACED NEAR THE CONSENSUS THROUGH TAU 48 AND THEN
FASTER THROUGH TAU 72, CLOSER TO THE GOOGLE DEEPMIND AND ECMWF,
WITH HIGH CONFIDENCE. INTENSITY GUIDANCE GENERALLY AGREES ON SLIGHT
INTENSIFICATION OR A STEADY INTENSITY THROUGH TAU 12 FOLLOWED BY
GRADUAL WEAKENING THROUGH TAU 72. HAFS-A IS THE MOST AGGRESSIVE
MODEL, SUGGESTING A PEAK INTENSITY OF 130 KTS. THE JTWC INTENSITY
FORECAST IS PLACED IN LINE WITH HAFS-A THROUGH TAU 36 AND THEN
SLIGHTLY LOWER, CLOSER TO THE CONSENSUS, THROUGH TAU 72 WITH MEDIUM
CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM//
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