WDPN31 PGTW 242100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 08W (EIGHT) WARNING 
NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.0N 152.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 391 NM EAST OF ALAMAGAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT TROPICAL
DEPRESSION 08W HAS BECOME MORE ELONGATED AND MAINTAINS A BROAD
STRUCTURE MORE REMINISCENT OF A MONSOON GYRE THAN A TROPICAL
CYCLONE, WITH A STRONG BELT OF WINDS AND CONVECTION ALONG THE
SOUTHERN AND EASTERN PERIPHERY, BUT A LACK OF CONVECTION AND STRONG
WINDS TO THE NORTH AND WEST. THE CIRCULATION ENVELOPE IS ENTANGLED
WITH THE EASTERN PERIPHERY OF AN UPPER-LEVEL TROUGH, WITH
ASSOCIATED DRY AIR ON THE WESTERN SIDE OF THE CIRCULATION. THE
EXACT CENTER POSITION OF 08W IS DIFFICULT TO ASSESS DUE TO CLOUD
COVER OBSCURATION AND A LACK OF RECENT SCATTEROMETER OR OTHER
SURFACE WIND DATA. A 241743Z SSMIS MICROWAVE PASS SHOWED THAT ONE
OR TWO SMALL-SCALE VORTICITY MAXIMA MAY EXIST WITHIN THE CURVED
CONVECTIVE BAND, BUT THE EVIDENCE IS NOT CONCLUSIVE. FOR NOW, THE
INITIAL POSITION IS SET BETWEEN THESE TWO POSSIBLE CENTER LOCATIONS
WITH LOW CONFIDENCE. THE INITIAL INTENSITY IS HELD AT 30 KT BASED
ON NO CHANGE IN SATELLITE PRESENTATION THAT WOULD SUGGEST ANY REAL
INTENSIFICATION IN RECENT HOURS, SUPPORTED BY OBJECTIVE
SATELLITE-BASED INTENSITY ESTIMATES FROM THE UNIVERSITY OF
WISCONSIN.

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

CURRENT STEERING MECHANISM: DEEP-LAYER RIDGE TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   CIMSS ADT: 41 KTS AT 241420Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EASTWARD
   OTHER FACTORS: DRY AIR MASS TO THE WEST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: DUE TO A PERSISTENT SHIFT IN MODEL
GUIDANCE OVER THE PAST DAY, THE FORECAST TRACK HAS BEEN SHIFTED
ABOUT 150 NM TO THE RIGHT (EAST) OF THE PREVIOUS ONE THROUGH 48
HOURS, AND OVER 200 NM FASTER THAN THE PREVIOUS ONE BEYOND 48
HOURS. 08W IS NOW EXPECTED TO MAKE ITS CLOSEST APPROACH TO HONSHU
IN AROUND 72 HOURS.

FORECAST DISCUSSION: TROPICAL DEPRESSION 08W IS STRUCTURED MORE
LIKE A MONSOON GYRE THAN A TRUE TROPICAL CYCLONE AT THE MOMENT.
THERE MAY BE MULTIPLE EMBEDDED SMALL-SCALE VORTICITY MAXIMA WITHIN
THE LONG BELT OF STRONG WINDS AND DEEP CONVECTION ON THE EASTERN
SIDE OF THE BROAD CIRCULATION ENVELOPE. OVER THE NEXT FEW DAYS,
NUMERICAL MODEL GUIDANCE IS SPLIT ON WHETHER ONE OF THESE SMALLER
EMBEDDED CIRCULATIONS WILL ANCHOR THE SYSTEM AND MAINTAIN A COMPACT
TROPICAL CYCLONE STRUCTURE THAT INTENSIFIES, OR THE STRONG
SOUTHERLY AND SOUTHEASTERLY ATMOSPHERIC CONVEYOR BELT WILL STRING
OUT THE SYSTEM TO THE POINT OF DISSIPATION. FOR NOW, GIVEN THE LACK
OF RECENT SURFACE WIND DATA TO ACCURATELY CHARACTERIZE THE
STRUCTURE OF ANY EXISTING EMBEDDED CIRCULATIONS, THE JTWC FORECAST
PRESUMES THAT A TROPICAL CYCLONE VORTEX WILL EXIST OVER THE NEXT 72
HOURS, RIDING UP THE SOUTHERN PERIPHERY OF A DEEP-LAYER RIDGE EAST
OF JAPAN, AND REMAINING ABOUT 200 NM EAST OF HONSHU. AFTER 72
HOURS, THERE IS SIGNIFICANT ALONG-TRACK SPREAD IN THE EXACT FORWARD
SPEED OF 08W IN NUMERICAL MODEL GUIDANCE AS IT TURNS NORTHEASTWARD
ALONG THE BAROCLINIC ZONE AND BECOMES EXTRATROPICAL AS IT IS
ABSORBED INTO A FRONTAL BOUNDARY. ONLY MILD INTENSIFICATION TO 40
KT IS EXPECTED OVER THE NEXT DAY OR TWO DUE TO THE DISORGANIZED AND
BROAD NATURE OF THE SYSTEM, BUT IT SHOULD BE NOTED THAT FURTHER
INTENSIFICATION COULD OCCUR IF A SMALLER-SCALE EMBEDDED CIRCULATION
DEVELOPS AND FORMS AN INNER CORE WINDFIELD. OVERALL CONFIDENCE IN
THE INTENSITY FORECAST IS LOWER THAN AVERAGE FOR THIS REASON.

MODEL DISCUSSION: THE JTWC FORECAST TRACK IS CLOSE TO THE
MULTI-MODEL CONSENSUS. THE JTWC INTENSIFY FORECAST IS LOWER THAN
THE MULTI-MODEL CONSENSUS DUE TO THE DISORGANIZED NATURE OF THE
SYSTEM WHICH IS NOT HANDLED WELL BY SOME MEMBERS OF THE CONSENSUS.

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