WDPN31 PGTW 030900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SEVENTEEN) 
WARNING NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.6N 157.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 999 NM EAST-SOUTHEAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TD 17W HAS STRUGGLED TO CONSOLIDATE DUE PRIMARILY TO SIGNIFICANT
DRY AIR ENTRAINMENT THROUGH THE MID- AND UPPER-LEVELS OF THE
SYSTEM. CONSEQUENTLY, DEEP CONVECTION IS ISOLATED TO THE SOUTHWEST
QUADRANT OF THE SYSTEM AND HAS DIMINISHED OVER THE PAST SIX HOURS.
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS LOW-LEVEL
CLOUD LINES WRAPPING INTO AN ELONGATED, FULLY EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC), WHICH PROVIDES HIGH CONFIDENCE IN THE
INITIAL POSITION. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH
HIGH CONFIDENCE BASED ON THE LATEST DVORAK INTENSITY ESTIMATES.
EQUATORWARD OUTFLOW REMAINS ROBUST DUE TO AN UPPER-LOW POSITIONED
TO THE SOUTHWEST.

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

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR) POSITIONED TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.0 - 25 KTS
   CIMSS ADT: 25 KTS AT 030230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   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: THE SYSTEM HAS TURNED NORTHWARD AND IS
FORECAST TO ACCELERATE NORTHEASTWARD THROUGH TAU 36 AS IT ROUNDS
THE NORTHWEST PERIPHERY OF THE STR. TD 17W WILL BEGIN TO ENCOUNTER
STRONG VERTICAL WIND SHEAR (25 KNOTS) ASSOCIATED WITH THE
MIDLATITUDE WESTERLIES AND COOLER SEA SURFACE TEMPERATURES (25-20C)
AFTER TAU 24, WHICH WILL LEAD TO DISSIPATION BY TAU 36. THE SYSTEM
IS NOT EXPECTED TO TRANSITION INTO A STRONG COLD CORE LOW DUE TO
THE LACK OF UPPER-LEVEL TROUGH SUPPORT BUT WILL LIKELY GET ABSORBED
INTO THE FRONTAL BOUNDARY NEAR OR NORTH OF 40N.     

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT
AGREEMENT AND SUPPORTS THE JTWC FORECAST TRACK WITH HIGH
CONFIDENCE. THERE IS MEDIUM CONFIDENCE IN THE JTWC INTENSITY
FORECAST WITH HWRF AND SHIPS (GFS) GUIDANCE INDICATING
INTENSIFICATION TO 35-40 KNOTS AFTER TAU 36 BUT THIS SCENARIO IS
CURRENTLY ASSESSED AS LOW PROBABILITY.  

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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