WDPN31 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 09W (NINE) WARNING 
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.6N 132.7E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 398 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
EXPOSED, BROAD LOW-LEVEL CIRCULATION CENTER (LLCC) POSITIONED ALONG 
THE WESTERN EDGE OF A SWATH OF DEEP CONVECTION ASSOCIATED WITH AN
EXTENSIVE SWATH OF CONVERGENT SOUTHERLY LOW-LEVEL FLOW. A 170930Z
SSMIS 91GHZ COMPOSITE MICROWAVE IMAGE REVEALS WEAKLY-DEFINED
SHALLOW BANDING WRAPPING AROUND AN ELONGATED, DEFINED LLCC. A
171202Z ASCAT-B BULLSEYE IMAGE CONTINUES TO INDICATE AN ELONGATED
CIRCULATION WITH A HIGHLY ASYMMETRIC WIND FIELD; AN EXPANSIVE SWATH
OF 30-35 KNOT SOUTHERLY WINDS OVER THE EASTERN SEMICIRCLE WITH
10-25 KNOT WINDS COVERING THE WESTERN SEMICIRCLE. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE ASCAT-B
IMAGE. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE DVORAK ESTIMATE FROM KNES AND THE OVERALL 
WIND FIELD. ENVIRONMENTAL ANALYSIS INDICATES MARGINALLY FAVORABLE 
CONDITIONS WITH CONVERGENT UPPER-LEVEL WESTERLIES AND MID-LEVEL DRY 
AIR ENTRAINMENT OVER THE WESTERN SEMICIRCLE OFFSET BY ROBUST 
POLEWARD AND EQUATORWARD OUTFLOW AND WARM SST VALUES.

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

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) CENTERED EAST
OF HONSHU (37N 140E) EXTENDING SOUTHWARD OVER THE NORTHEASTERN AND
EASTERN PERIPHERY OF THE SYSTEM.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 35 KTS AT 171140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: MID-LEVEL DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   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 09W IS TRACKING NORTHWESTWARD ALONG THE
PERIPHERY OF THE STR BUT IS EXPECTED TO GRADUALLY TURN
WEST-NORTHWESTWARD AS A DEEP UPPER LOW CURRENTLY LOCATED WEST OF
KYUSHU FILLS AND SHIFTS WEST ALLOWING THE STR TO BUILD OVER THE
EAST CHINA SEA BY TAU 48. TD 09W IS CURRENTLY STRUGGLING TO
CONSOLIDATE DUE PRIMARILY TO THE CONVERGENCE ALOFT AND DRY AIR
ENTRAINMENT, THEREFORE, TD 09W SHOULD SLOWLY INTENSIFY THROUGH TAU
24. AFTER TAU 24, ENVIRONMENTAL CONDITIONS SHOULD GRADUALLY
IMPROVE AS THE UPPER LOW AND CONVERGENCE ALOFT WEAKEN ALLOWING THE 
SYSTEM TO VENT AND SUSTAIN MORE CENTRALIZED DEEP CONVECTION, WHICH 
WILL MOISTEN THE MID-LEVELS. THIS SHOULD LEAD TO A FASTER RATE OF 
INTENSIFICATION WITH A PEAK OF 85 KNOTS ANTICIPATED BY TAU 120.    

MODEL DISCUSSION: DUE TO THIS EVOLVING SYNOPTIC PATTERN, THERE IS
INCREASING UNCERTAINTY IN THE TRACK FORECAST AFTER TAU 48.
NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT THROUGH TAU 48 WITH A
85NM SPREAD IN SOLUTIONS AT TAU 48. AFTER TAU 48, MODEL GUIDANCE
DIVERGES WITH JGSM INDICATING A FASTER NORTHWESTWARD TRACK JUST
SOUTH OF SHANGHAI, CHINA, AND GFS AND UKMET INDICATING A SHARPER
WESTWARD TURN TOWARD NORTHERN TAIWAN. THE BULK OF THE GUIDANCE
SUPPORTS THE JTWC TRACK FORECAST WITH LOW CONFIDENCE IN THE
EXTENDED PERIOD. THERE IS LOW CONFIDENCE IN THE JTWC INTENSITY
FORECAST IN THE EXTENDED PERIOD WITH A LARGE SPREAD IN INTENSITY
GUIDANCE ASSOCIATED WITH THE COMPLEX, EVOLVING ENVIRONMENT.  

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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