Advisories

WDPN31 PGTW 312100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 034//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.9N 144.0E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 187 NM SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: EASTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON 
(TY) 30W (IN-FA) WITH AN INCREASINGLY RAGGED EYE THAT HAS COOLED TO 12 
C AND A CENTRAL DENSE OVERCAST (CDO) THAT HAS BECOME MORE 
ASYMMETRICAL, DETERIORATING IN THE SOUTHWESTERN QUADRANT. A DRY SLOT 
TEMPORARILY BREACHED THE SOUTHWESTERN PORTION OF THE EYEWALL, 
COINCIDING WITH A 311517Z AMSR-3 PASS THAT CONFIRMED THE COMPLETION OF 
THE PREVIOUS EYEWALL REPLACEMENT CYCLE (ERC) AS THE INNER EYEWALL HAD 
ERODED ON THE SOUTHERN SEMICIRCLE AND THE NOW PRIMARY, LARGER EYEWALL 
IS WEAKEST IN THE SOUTHWESTERN QUADRANT BUT OTHERWISE 
ROBUST AND WITH A DEVELOPING CONVECTIVE BAND TO THE NORTH.
ENVIRONMENTAL CONDITIONS ARE ASSESSED AS MARGINAL, WITH CONTINUED DRY 
AIR ENTRAINMENT, LOW (10-15 KTS) VERTICAL WIND SHEAR, STRONG POLEWARD
AND RADIAL OUTFLOW ALOFT, AND WARM (27-28C) SEA SURFACE TEMPERATURES, 
ALTHOUGH THE CONTINUED SLOW IN TRACK SPEED IS EXPECTED TO CAUSE 
IMMINENT UPWELLING OF COOLER SSTS UNDERNEATH 30W. THE INITIAL POSITION 
IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE WELL-DEFINED EYE IN 
IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE 
BASED ON THE MODERATELY INCREASING SPREAD ACROSS AGENCY DVORAK FIXES 
AND CIMSS OBJECTIVE ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT COMPRISED OF
A COL BETWEEN SUBTROPICAL RIDGES CENTERED TO THE EAST AND WEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T5.0 - 90 KTS
   CIMSS SATCON: 100 KTS AT 311555Z
   CIMSS ADT: 94 KTS AT 311730Z
   CIMSS AIDT: 100 KTS AT 311730Z
   CIMSS D-MINT: 101 KTS AT 311557Z
   CIMSS D-PRINT: 104 KTS AT 311730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: OCEANIC UPWELLING; DRY AIR ENTRAINMENT

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 30W HAS SLOWED IN TRACK SPEED, OSCILLATING
SLIGHTLY AND TURNING EASTWARD AS IT BEGINS AN EXPECTED SMALL CLOCKWISE 
LOOP IN THE NEXT 12 HOURS. THE STEERING ENVIRONMENT IS VERY WEAK AS 
30W LIES IN A COL BETWEEN SUBTROPICAL RIDGES (STRS) CENTERED TO THE 
EAST AND WEST OF THE SYSTEM, AND A MID-LATITUDE TROUGH PASSES TO ITS 
NORTH. BY TAU 24, THE PASSING TROUGH IS EXPECTED TO WEAKEN THE STR TO 
THE EAST, ALLOWING THE BUILDING EASTWARD EXTENSION OF THE WESTERN STR 
TO STEER 30W WESTWARD. THE ENTIRE STEERING RIDGE COMPLEX IS ALSO 
EXPECTED TO SHIFT WESTWARD WHILE THE TWO STRS RETAIN THEIR ORIENTATION 
TO EACH OTHER, AND BY TAU 48 THE EASTERN STR IS EXPECTED TO REBUILD 
AND REGAIN STEERING CONTROL, CAUSING 30W TO TURN POLEWARD AND THEN 
NORTHEAST AS IT ROUNDS THE AXIS OF THE EASTERN STR. EXTRATROPICAL 
TRANSITION (ETT) IS EXPECTED TOBEGIN AT TAU 96 AS 30W NEARS THE UPPER-
LEVEL WESTERLIES AND WILL COMPLETE BY TAU 120, ALONG WITH AN INCREASE 
IN TRACK SPEED AS IT BECOMES POLEWARD OF THE STR AXIS. REGARDING 
INTENSITY, IMMINENT WEAKENING IS EXPECTED AS THE SLOW IN THE TRACK 
SPEED OF 30W CAUSES IT TO REMAIN OVER UPWELLED COOLER SSTS. BEYOND TAU 
24, A PLATEAU IS EXPECTED AS TRACK SPEED INCREASES AND 30W ESCAPES ITS 
COOL WAKE, FOLLOWED BY A BRIEF PERIOD OF REINTENSIFICATION AS OUTFLOW 
ALOFT IS ENHANCED NEAR THE AXIS OF THE STR. BEYOND TAU 60, STEADY 
WEAKENING IS EXPECTED AS VWS WILL SHARPLY INCREASE AS IN-FA APPROACHES 
THE STRONG UPPER-LEVEL WESTERLIES AN AREA OF LOWER OCEAN HEAT CONTENT.

MODEL DISCUSSION: THE MODEL TRACK GUIDANCE PACKAGE HAS SHIFTED 
SLIGHTLY WESTWARD, WITH ALL MODELS DEPICTING A SLIGHTLY WIDER 
RECURVATURE AROUND THE EASTERN STR, CAUSING A 270 NM CROSS-TRACK 
SPREAD AT TAU 96. AI MODELS REMAIN THE EASTERNMOST WHILE UKMET, UKMET 
ENSEMBLE, AND NAVGEM REMAIN THE WESTERNMOST OUTLIERS. BEYOND TAU 72, 
ALONG-TRACK SPEED GREATLY DIVERGES AS AI-BASED MODELS, GFS, AND GFS-
BASED COAMPS-TC SIGNIFICANTLY OUTPACE THE REMAINDER OF PHYSICS-BASED 
MODELS, RESULTING IN AN ALONG-TRACK SPREAD OF 850 NM AT TAU 120 
BETWEEN THE SLOWEST, UKMET, AND THE FASTEST, AI GFS. THE OFFICIAL JTWC 
FORECAST TRACK IS ASSESSED WITH MEDIUM CONFIDENCE OUT TO TAU 72 AND 
LOW CONFIDENCE THEREAFTER, IN LINE WITH THE AI CONSENSUS OUT TO TAU 72 
AND THEN SLOWER THEREAFTER, IN LINE WITH THE TRACK AND TRACK SPEED 
DEPICTED BY GOOGLE DEEPMIND AND EXPERIMENTAL WEATHERMESH. MODEL 
INTENSITY GUIDANCE IS IN FAIR AGREEMENT ON AN INITIAL WEAKENING 
FOLLOWED BY A BRIEF PLATEAU OR REINTENSIFICATION AND THEN STEADY 
WEAKENING AFTER TAU 60. THE ONLY NOTABLE OUTLIERS ARE BOTH GOOGLE 
DEEPMIND MODELS, WHICH DEPICT A STEADY WEAKENING TREND THROUGHOUT THE 
FORECAST PERIOD WITHOUT ANY PLATEAU OR STRENGTHENING. THE OFFICIAL 
JTWC INTENSITY FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE OUT TO TAU 
72 AND LOW CONFIDENCE THEREAFTER, IN GOOD AGREEMENT WITH GFS-BASED 
COAMPS-TC AND THE MULTI-MODEL CONSENSUS.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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