Advisories

WDPN32 PGTW 300300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (ETAU) WARNING 
NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.9N 164.7E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 696 NM NORTHEAST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION (TD) 21W (ETAU) AS A FULLY EXPOSED AND COMPACT LOW-LEVEL
CIRCULATION CENTER (LLCC). THE 292226Z ASCAT DATA REVEALS THE
NORTHWESTERN AND SOUTHEASTERN QUADRANTS ARE EXTREMELY STRETCHED,
WITH WEAKER (10 KTS) WINDS DOMINATING THE SOUTHEASTERN QUADRANT AS
TROPICAL STORM 20W PASSES 21W TO THE EAST. AS A RESULT OF THE
BINARY INTERACTION, 21W HAS REMAINED QUASISTATIONARY OVER THE PAST
6 HOURS. ENVIRONMENTAL ANALYSIS REVEALS AN UNFAVORABLE ENVIRONMENT,
CHARACTERIZED BY HIGH (25-30KTS) VERTICAL WIND SHEAR, DRY AIR
ENTRAINMENT, MARGINAL (0-20 KJ PER CM2) OCEAN HEAT CONTENT, AND
TEMPERATE (26-27 C) SEA SURFACE TEMPERATURES (SST). THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE FULLY EXPOSED
LLCC. THE INITIAL INTENSITY OF 25 KTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE AFOREMENTIONED 292226Z ASCAT DATA REVEALING
MAXIMUM WINDS OF 25 KTS.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: BINARY INTERACTION WITH TROPICAL STORM
(TS) 20W

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 31 KTS AT 300140Z
   CIMSS AIDT: 31 KTS AT 300140Z
   CIMSS D-PRINT: 36 KTS AT 300110Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TD 21W IS FORECAST TO REMAIN QUASISTATIONARY,
DRIFTING SLOWLY NORTHEASTWARD AS 20W TRACKS POLEWARD. AROUND TAU
12, 20W WILL TRACK FAR ENOUGH AWAY AND RELEASE 21W FROM ITS
INFLUENCE, ALLOWING 21W TO INCREASE TRACK SPEEDS. 21W WILL TRACK
NORTHEASTWARD THROUGH THE END OF THE FORECAST AT TAU 48. THE
POTENTIAL FOR AN EQUATORWARD LOOP MENTIONED IN PREVIOUS FORECAST IS
LOOKING LESS LIKELY AS 20W IS NOW AT A HIGHER LATITUDE THAN 21W. AS
A RESULT, 21W IS EXPECTED TO TRACK DIRECTLY POLEWARD WITHOUT AN
EQUATORWARD DETOUR. AS 21W TRACKS POLEWARD, IT WILL ENCOUNTER
INCREASINGLY HOSTILE CONDITIONS, WITH SSTS DROPPING BELOW 26C BY
TAU 12 AND VWS INCREASING UP TO 30 KTS BY TAU 48, ULTIMATELY
INDUCING SUBTROPICAL TRANSITION BY TAU 36. 21W IS FORECAST TO
COMPLETE SUBTROPICAL TRANSITION BY TAU 48.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE REMAINS IN
POOR, BUT IMPROVING, AGREEMENT. PREVIOUSLY, SEVERAL RELIABLE MODELS
INDICATED AN EQUATORWARD LOOP. THIS FORECAST, HOWEVER, THAT NUMBER
HAS REDUCED TO THREE MODELS AND THEY ARE ALL GFS-BASED. ALL OTHER
MODELS DEPICT A DIRECTLY POLEWARD TRACK. DISREGARDING THE THREE
OUTLIERS, THERE REMAINS SIGNIFICANT DISCREPACY IN THE ALONG TRACK
DIRECTION. THE JTWC TRACK FORECAST MAINTAINS VERY SLOW TRACK
MOTIONS THROUGH TAU 12 AS A RESULT OF THE OBSERVED QUASISTATIONARY
PERIOD. AFTER TAU 12, THE JTWC TRACK FORECAST IS IN CLOSE AGREEMENT
WITH EXPERIMENTAL GOOGLE DEEPMIND AND THE HISTORICALLY
HIGH-PERFORMING EXPERIMENTAL MULTI-AI MODEL CONSENSUS. TRACK
FORECAST CONFIDENCE IS OVERALL LOW. RELIABLE INTENSITY AIDS ARE IN
POOR AGREEMENT. THE JTWC INTENSITY FORECAST IS IN CLOSE ALIGNMENT
WITH THE HAFS-A SOLUTION AND THE MULTI-MODEL CONSENSUS WITH LOW
CONFIDENCE.

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