WDPN32 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (HALONG) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 32.5N 139.4E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 169 NM SOUTH OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 39 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A RAGGED 
EYE APPROXIMATELY 20 NM IN DIAMETER, WITH ROBUST POLEWARD OUTFLOW AND
ACCOMPANYING CIRRUS FILAMENTS. ANIMATED WATER VAPOR IMAGERY DEPICTS 
THE WESTERN FLANK OF TYPHOON (TY) 28W WEAKENING UNDER HIGH (25-30 
KTS) VERTICAL WIND SHEAR (VWS) AND THE OVERALL DRY ENVIRONMENT. 
ANALYSIS INDICATES A MARGINAL ENVIRONMENT, CHARACTERIZED BY HIGH VWS, 
BORDERLINE (26-27 C) SEA SURFACE TEMPERATURES (SST), AND DRY AIR 
SURROUNDING 28W. 28W APPEARS TO BE UNDERGOING AN EYEWALL REPLACEMENT 
CYCLE (ERC), EVIDENCED BY THE CONCENTRIC EYEWALLS IN AN 080844Z RCM-3 
SAR IMAGE AND A CLEAR MOAT ALONG THE WESTERN SEMICIRCLE VISIBLE IN 
ANIMATED EIR. SURFACE OBSERVATIONS FROM HACHIJO-JIMA, APPROXIMATELY 
40 NM NORTHEAST OF THE 1800Z CENTER, INDICATES PEAK WINDS OF 62KTS 
(10-MINUTE AVERAGE) WITH MINIMUM SEA LEVEL PRESSURE OF 968.7 MB. THE 
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON ANIMATED 
RADAR IMAGERY AND A 081800Z HM9 EIR IMAGE DEPICTING THE EYE. THE 
INITIAL INTENSITY OF 110 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED 
ON THE AGENCY DVORAK FIXES AND OBJECTIVE INTENSITY AIDS LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) TO THE
SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T5.5 - 102 KTS
   CIMSS SATCON: 107 KTS AT 081708Z
   CIMSS ADT: 115 KTS AT 081800Z
   CIMSS AIDT: 104 KTS AT 081800Z
   CIMSS D-MINT: 107 KTS AT 081617Z
   CIMSS D-PRINT: 103 KTS AT 081830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: 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 28W (HALONG) IS FORECAST TO CONTINUE ITS
EAST-NORTHEASTWARD TRACK MOVEMENT, ACCELERATING AS IT ROUNDS THE
NORTHWESTERN PERIPHERY OF THE DEEP-LAYER STR TO ITS SOUTHEAST. 28W
WILL BEGIN EXTRATROPICAL TRANSITION (ETT) NO LATER THAN TAU 12,
WITH ETT COMPLETE AROUND TAU 36. HALONG HAS BEGUN CONSISTENTLY
WEAKENING AND IS EXPECTED TO RAPIDLY DETERIORATE BEGINNING AROUND
TAU 12 DUE TO THE WORSENING ENVIRONMENTAL CONDITIONS (COOLER SST,
INCREASING DRY AIR) AND INTERACTION WITH THE UPPER-LEVEL WESTERLIES. 

MODEL DISCUSSION: DETERMINISTIC TRACK MODEL GUIDANCE IS IN TIGHT
AGREEMENT FOR THE DURATION OF THE FORECAST PERIOD, BOASTING A 45NM
CROSS-TRACK SPREAD AND A 110NM ALONG-TRACK SPREAD AT TAU 36. AS A
RESULT, THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE.
RELIABLE INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON A CONSISTENT
AND RAPID WEAKENING TREND, LENDING HIGH CONFIDENCE TO THE JTWC
INTENSITY FORECAST.

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