Advisories

WDPN32 PGTW 041500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 26W (CHOI-WAN) WARNING 
NR 019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.3N 146.9E
   INITIAL INTENSITY: 135 KTS
   GEOGRAPHIC REFERENCE: 320 NM EAST-SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 48 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS SUPER
TYPHOON 26W (CHOI-WAN) WITH A HIGHLY SYMMETRICAL CENTRAL DENSE
OVERCAST SURROUNDING A WELL-DEFINED 19 NM EYE. THE PRESENTATION
OF THE SYSTEM APPEARS TO HAVE PEAKED AT AROUND 040900Z WITH THE 
COLD MEDIUM GRAY (CMG) SHADE IN THE DVORAK ENHANCED IR IMAGERY 
COMPLETELY SURROUNDING THE EYEWALL. AT 041200Z, THE CMG HAS LESSENED 
AS CLOUD TOPS HAVE SLIGHTLY WARMED SINCE THE LIKELY PEAK 3 HOURS 
EARLIER. THE WARMING TREND IN THE CLOUD TOPS IS LIKELY DUE TO AN 
ONGOING EYEWALL REPLACEMENT CYCLE (ERC) THAT WAS CONFIRMED BY A 
040957Z GMI 37 GHZ MICROWAVE IMAGE SHOWING A CLEAR MOAT FEATURE 
SURROUNDING THE COMPACT INNER CORE. THE INITIAL POSITION IS PLACED 
WITH HIGH CONFIDENCE BASED ON THE DEFINED EYE IN ANIMATED EIR IMAGERY 
AND THE GMI IMAGE. THE INITIAL INTENSITY OF 135 KTS IS ASSESSED WITH 
MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES OF T6.5-7.0 AND 
THE CIMSS INTENSITY ESTIMATES LISTED BELOW. THE INITIAL WIND RADII 
ARE PLACED WITH HIGH CONFIDENCE BASED ON THE 041035Z METOP-B AND 
041057Z METOP-C ASCAT PASSES.

INITIAL WIND RADII BASIS: 041035Z METOP-B AND 041057Z METOP-C ASCAT
SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T6.5 - 127 KTS
   RCTP: T7.0 - 140 KTS 
   CIMSS ADT: 129 KTS AT 041140Z
   CIMSS AIDT: 128 KTS AT 041140Z
   CIMSS D-MINT: 135 KTS AT 041202Z
   CIMSS D-PRINT: 127 KTS AT 041140Z

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

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: 26W IS FORECAST TO TRACK GENERALLY NORTHWARD
ALONG THE WESTERN PERIPHERY OF THE STR TO THE EAST THROUGH TAU 36.
NEAR TAU 36, 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 48,
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 BEGIN GRADUALLY WEAKENING 
AT A STEADY RATE OF 10 KTS PER 12 HOURS THROUGH TAU 60. THE WEAKENING 
TREND MAY BE AUGMENTED DEPENDING ON THE TIMING AND SEVERITY OF THE 
ERC. IF THE OUTER EYEWALL COMPLETELY CHOKES THE INNER EYEWALL, THEN 
THERE IS A POTENTIAL FOR A MORE RAPID RATE OF WEAKENING. IF THE ERC 
DOES NOT FULLY COMPLETE, THEN THERE IS EVEN A CHANCE FOR BRIEF 
REDEVELOPMENT WITHIN THE NEXT 12 HOURS. AFTER TAU 12, OCEAN HEAT 
CONTENT WILL BEGIN TO DROP, AIDING IN THE WEAKENING TREND. STARTING 
AROUND TAU 48, SEA SURFACE TEMPERATURES WILL COOL AND WESTERLY 
VERTICAL WIND SHEAR WILL QUICKLY INCREASE, FURTHER SUPPORTING THE 
WEAKENING TREND. NOTABLY, 26W WILL TAP INTO AN EXTREME POLEWARD 
OUTFLOW CHANNEL LEADING UP TO THE COMPLETION OF ETT, SUPPORTED BY A 
VERY STRONG JET MAXIMUM TO THE NORTH. AS A RESULT, 26W IS FORECAST 
TO MAINTAIN TYPHOON INTENSITY THROUGH THE TRANSITION. AT TAU 72, 
SHEAR IS EXPECTED TO BE WELL OVER 60 KTS AND DRY AIR WILL BE ENGULFING 
THE VORTEX AS THE SYSTEM TRANSITIONS INTO A POTENT COLD-CORE LOW.

MODEL DISCUSSION: MODEL TRACK GUIDANCE CONTINUES TO BE IN GOOD 
AGREEMENT THROUGHOUT THE FORECAST PERIOD WITH CROSS-TRACK SPREAD AT
TAU 72 MEASURED TO BE 120 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 250 NM WITH GFS CONTINUING TO BE THE
SLOWEST TRACKER (BESIDES NAVGEM, WHICH IS UNREALISTICALLY SLOW).
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 AGREES ON STEADY
WEAKENING THROUGHOUT THE FORECAST PERIOD WITH NO NOTABLE OUTLIERS
PRESENT. THE JTWC INTENSITY FORECAST IS PLACED VERY CLOSE TO THE
MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE. THE EXACT WEAKENING
TREND REMAINS SOMEWHAT UNCERTAIN DUE TO THE INHERENT UNCERTAINTIES
REVOLVING AROUND THE ERC DYNAMICS. 

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