Advisories

WDPN31 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 038//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.0N 143.0E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 192 NM SOUTH-SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: WESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS THE
CONTINUED DETERIORATING APPEARANCE OF TYPHOON (TY) 30W (IN-FA) AS
IT HAS LOST A DISCERNIBLE EYE FEATURE IN EIR, WITH ONLY AN
INTERMITTENT, SMALL WARM SPOT MEASURING ROUGHLY -50 C. A 011550Z
AMSR-3 SUITE REVEALS THE CONVECTION CONTINUING TO ERODE ON THE
WESTERN FLANK AS DRY AIR CONTINUES TO ENTRAIN IN AND DEGRADE THE
CENTRAL DENSE OVERCAST (CDO). ENVIRONMENTAL CONDITIONS ARE ASSESSED
AS MARGINALLY UNFAVORABLE AS THE DRY AIR AND COOL (24-26 C) SEA
SURFACE TEMPERATURES (SSTS) BEING UPWELLED BY THE SLOW TRACK OF 30W
ARE BEING SOMEWHAT OFFSET BY LOW (5-10 KTS) VERTICAL WIND SHEAR
(VWS) AND STRONG POLEWARD OUTFLOW ALOFT. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE SATELLITE DATA. THE
INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, IN GOOD
AGREEMENT WITH AGENCY DVORAK FIXES AND SLIGHTLY ABOVE CIMSS
OBJECTIVE ESTIMATES.

INITIAL WIND RADII BASIS: 01118Z METOP-C ASCAT DATA

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT BETWEEN
SUBTROPICAL RIDGES CENTERED TO THE EAST AND WEST OF 30W

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.5 - 77 KTS
   CIMSS SATCON: 85 KTS AT 011634Z
   CIMSS ADT: 87 KTS AT 011730Z
   CIMSS AIDT: 76 KTS AT 011730Z
   CIMSS D-MINT: 82 KTS AT 011635Z
   CIMSS D-PRINT: 73 KTS AT 011830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 5-10 KTS
   SST: 25-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT; OCEANIC UPWELLING

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 CONTINUED SLOWLY WESTWARD AS IT
REMAINS IN THE WEAK STEERING ENVIRONMENT BETWEEN THE SUBTROPICAL
RIDGES (STRS) CENTERED TO THE EAST AND WEST OF THE SYSTEM. TRACK
SPEED IS EXPECTED TO SLIGHTLY INCREASE BUT REMAIN RELATIVELY SLOW
AS THE ENTIRE STEERING RIDGE COMPLEX TRANSLATES WESTWARD AND 30W
REMAINS IN THE COL BETWEEN THE STRS. BY TAU 24, THE PASSING OF A
MID-LATITUDE TROUGH TO THE NORTH IS EXPECTED TO WEAKEN THE WESTERN
STR, ALLOWING THE EASTERN STR TO REGAIN PRIMARY STEERING CONTROL,
INDUCING A POLEWARD TURN BY TAU 36 AND ACCELERATION IN TRACK SPEED
BY TAU 72 AS 30W ROUNDS THE STR AXIS AND TURNS NORTHEASTWARD.
EXTRATROPICAL TRANSITION (ETT) IS EXPECTED TO BEGIN NO LATER THAN
TAU 96 AND COMPLETE NO LATER THAN TAU 120 AS 30W CROSSES THE 26 C
ISOTHERM AND APPROACHES THE BAROCLINIC ZONE. REGARDING INTENSITY,
30W IS EXPECTED TO WEAKEN IN THE SHORT TERM AS IT REMAINS OVER ITS
UPWELLED COOL WAKE. ONCE TRACK SPEED INCREASES, INTENSITY WILL
PLATEAU AS IT MOVES OVER WARMER SSTS, FOLLOWED BY A PERIOD OF
MODEST INTENSIFICATION BETWEEN TAUS 36 AND 60 AS IT NEARS THE AXIS
OF THE STR AND OUTFLOW ALOFT INCREASES. THEREAFTER, WEAKENING IS
FORECAST FOR THE REMAINDER OF THE FORECAST PERIOD AS VWS SHARPLY
INCREASES WITH THE APPROACH TO THE UPPER-LEVEL WESTERLIES AND ONSET
OF ETT. 

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT OUT TO
TAU 72 WHILE UKMET ENSEMBLE, JGSM, AND GALWEM REMAIN OUTLIERS TO
THE WEST. BEYOND TAU 72, TRACK SPEED CONTINUES TO DIVERGE WITH GFS,
BOTH GOOGLE DEEPMINDS, AND THE AI GEFS MEAN MAKING UP THE FASTEST
MEMBERS, WHILE GALWEM, UKMET ENSEMBLE, AND NAVGEM COMPRISE THE
SLOWEST MEMBERS. THE OFFICIAL JTWC FORECAST IS THUS ASSESSED WITH
MEDIUM CONFIDENCE OUT TO TAU 72 IN LINE WITH THE AI CONSENSUS AND
LOW CONFIDENCE THEREAFTER, SLIGHTLY SLOWER THAN THE AI CONSENSUS.
MODEL INTENSITY GUIDANCE IS IN POOR AGREEMENT FOR THE ENTIRETY OF
THE FORECAST PERIOD, WITH GFS AND BOTH GOOGLE DEEPMINDS PREDICTING
STEADY WEAKENING, WHILE DECAY SHIPS, HAFS-A, AND COAMPS-TC ALL
DEPICT SOME KIND OF RE-INTENSIFICATION BETWEEN TAUS 36 AND 72. ALL
MODELS DEPICT WEAKENING AFTER TAU 72 BUT HAVE A SPREAD OF 40 KTS AT
TAU 120. THE OFFICIAL JTWC INTENSITY FORECAST IS THUS ASSESSED WITH
LOW CONFIDENCE THROUGHOUT, IN LINE WITH THE MULTI-MODEL CONSENSUS
BUT DIVERGING BELOW IT PAST TAU 72 AS THE OFFICIAL FORECAST TRACK
OUTPACES THAT OF THE MULTI-MODEL CONSENSUS AND THUS FASTER
WEAKENING IS EXPECTED.

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