Advisories

WDPN33 PGTW 071500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 14W (CHAN-HOM) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.0N 159.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 1064 NM EAST-SOUTHEAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION (TD) 14W (CHAN-HOM) AS A BARE AND FULLY EXPOSED LOW-LEVEL 
CIRCULATION CENTER (LLCC) COMPLETELY DEVOID OF CONVECTION SAVE FOR A 
PITIFUL PLUME OF CENTRAL CONVECTION WEAKLY RISING FROM THE LLCC. DRY 
AIR CONTINUES TO ENVELOP THE SYSTEM, WRAPPING INTO THE CORE FROM THE 
SOUTH. THE 071058Z ASCAT DATA REVEALS THE SYSTEM HAS WEAKENED 
UNEXPECTEDLY AND THE ELEVATED WINDS THAT ONCE WRAPPED AROUND THE 
WESTERN PERIPHERY OF THE SYSTEM HAVE DISSIPATED. THE WIND FIELD 
REMAINS HIGHLY ASYMMETRIC, WITH A VAST SWATH OF 25-30 KT WINDS 
EXTENDING THE ENTIRETY OF THE NORTHEASTERN SEMICIRCLE. THE 
SOUTHWESTERN SEMICIRCLE IS SIGNIFICANTLY WEAKER, WITH A LARGE PATCH OF 
5-10 KTS EXTENDING SOUTHWESTWARD FROM THE CENTER. ENVIRONMENTAL 
ANALYSIS REVEALS AN UNFAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE 
TO HIGH (20-25 KTS) VERTICAL WIND SHEAR (VWS), MARGINALLY FAVORABLE 
(26-27 C) SEA SURFACE TEMPERATURES (SST), AND WEAK POLEWARD OUTFLOW. 
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE FULLY 
EXPOSED LLCC. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE AFOREMENTIONED 071058Z ASCAT DATA.

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

CURRENT STEERING MECHANISM:  SOUTHWESTERN PERIPHERY OF A WESTWARD
EXTENSION OF THE SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS ADT: 31 KTS AT 071310Z
   CIMSS AIDT: 33 KTS AT 071310Z
   CIMSS D-MINT: 30 KTS AT 071156Z
   CIMSS D-PRINT: 30 KTS AT 071310Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: FORECAST INTENSITIES HAVE BEEN
LOWERED TO REFLECT THE HIGH CONFIDENCE INITIAL INTENSITY AND
GRADUAL RATE OF DEVELOPMENT

FORECAST DISCUSSION: TS 14W IS FORECAST TO CONTINUE TRACKING 
NORTHWESTWARD WHILE IT REMAINS UNDER THE STEERING INFLUENCE OF THE 
WEAK STR CENTERED TO ITS NORTHEAST. BETWEEN TAU 24-36, A DEEP TROUGH 
WILL WEAKEN THE RIDGE AND INDUCE A WEAKER STEERING ENVIRONMENT. 14W IS 
FORECAST TO SLOW TRACK SPEEDS AND TURN POLEWARD INTO THE WEAKNESS IN 
THE RIDGE BETWEEN TAU 36-60. FOLLOWING THE PASSAGE OF THE TROUGH 
AROUND TAU 72, THE STR WILL REBUILD AND DRIVE 14W WESTWARD THROUGH TAU 
120. TOWARDS THE END OF THE FORECAST PERIOD, A SHALLOW STR OVER THE 
SEA OF JAPAN WILL BUILD AND CAUSE 14W TO TRACK DUE WESTWARD AGAIN 
BETWEEN TAU 96-120. REGARDING INTENSITY, 14W IS EXPECTED TO GRADUALLY 
INTENSIFY THROUGH TAU 72 AS THE ENVIRONMENT SLOWLY BECOMES MORE 
FAVORABLE. VWS IS EXPECTED TO EASE SLIGHTLY BY TAU 24 AND ALLOW FOR 
SLIGHT INTENSIFICATION. HOWEVER, BY AROUND TAU 72, SSTS ARE EXPECTED 
TO BECOME UNFAVORABLE AND INDUCE WEAKENING THROUGH THE REMAINDER OF 
THE FORECAST PERIOD. DRY AIR ENTRAINMENT IS ANTICIPATED TO BE A 
PERSISTENT INHIBITOR TO INTENSIFICATION THROUGHOUT THE FORECAST. 
ADDITIONALLY, 14W IS EXPECTED TO REMAIN POSITIONED IN CLOSE PROXIMITY 
TO AN UPPER-LEVEL LOW THROUGH TAU 120. 14W IS FORECAST TO BEGIN 
SUBTROPICAL TRANSITION NO LATER THAN TAU 96 AND BE COMPLETE BY TAU 
120.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN MODERATE 
AGREEMENT THROUGH TAU 72, WITH MILD DISAGREEMENT REGARDING THE SLOWED 
TRACK SPEED AND CONFUSED STEERING ENVIRONMENT INDUCED BY THE UPPER 
LEVEL TROUGH. AS A RESULT, THE JTWC TRACK IS PLACED WITH MEDIUM 
CONFIDENCE FROM TAU 0-72. FOLLOWING TAU 72, TRACK GUIDANCE DIVERGES 
SIGNIFICANTLY IN THE CROSS-TRACK DIRECTION, CAUSING UNCERTAINTY WITH 
THE LATE-TERM TRACK FORECAST. THE CROSS-TRACK SPREAD AT TAU 96 
(APPROXIMATELY WHEN 14W WILL BE MAKING LANDFALL IN JAPAN) IS 250 NM, 
WITH GEFS MEAN THE EQUATORWARD-MOST MEMBER AND GALWEM THE POLEWARD-
MOST MEMBER. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-
MODEL CONSENSUS WITH LOW CONFIDENCE FROM TAU 72-120. RELIABLE 
INTENSITY AIDS ARE IN STRONG AGREEMENT THROUGHOUT THE FORECAST, 
SUPPORTING THE JTWC INTENSITY FORECAST WITH HIGH CONFIDENCE. THE JTWC 
INTENSITY FORECAST IS CLOSELY ALIGNED WITH THE MULTI-MODEL CONSENSUS 
AND THE HAFS-A SOLUTION.

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