WDPN32 PGTW 130300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (NAMTHEUN) 
WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.0N 152.5E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 156 NM SOUTH-SOUTHWEST OF MINAMI TORI
SHIMA
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
WHILE TD 23W HAS STRUGGLED MIGHTILY AGAINST STRONG AND PERSISTENT
SOUTHERLY SHEAR, IT APPEARS TO HAVE LOST THE BATTLE AND BEGUN THE
SLOW DECLINE TO ITS ULTIMATE DEMISE. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI) REVEALS A SMALL AREA OF FLARING CONVECTION
SHEARED TO THE NORTHEAST OF AN ELONGATED LOW LEVEL CIRCULATION
CENTER (LLCC), THE WESTERN BANDS OF WHICH ARE EVIDENT IN THE CLEAR
REGION WEST OF THE CIRRUS SHIELD. A 122132Z ASCAT-A PASS SHOWED THE
LLCC BEGINNING TO STRETCH OUT ALONG A SOUTHWEST-NORTHEAST AXIS, AND
EXTRAPOLATION OF THIS DATA, COMBINED WITH THE PARTIALLY EXPOSED
LLCC IN THE VISIBLE IMAGERY, LENT HIGH CONFIDENCE TO THE INITIAL
POSITION. THE AGENCY CURRENT INTENSITY ESTIMATES RANGED FROM 2.0 TO
2.5, WHICH ALIGNS CLOSELY WITH THE ADT ESTIMATE COMING IN RIGHT AT
THE AVERAGE AT 32 KNOTS. THE PREVIOUSLY MENTIONED ASCAT CONFIRMED
THE 30 KNOT INITIAL INTENSITY ESTIMATE, SHOWING A PATCH OF 30 KNOT
WIND BARBS CONSTRAINED TO THE NORTHEAST SECTOR, UNDER THE FLARING
CONVECTION. INTERESTINGLY, CIMSS SHEAR ANALYSIS INDICATES THE
OVERALL SHEAR ENVIRONMENT HAS IMPROVED, WITH THE MEAN SHEAR
MAGNITUDE NOW ESTIMATED AT 19 KNOTS. HOWEVER, LIKELY THIS IS TOO
LOW, BASED ON THE SATELLITE DEPICTION. THE UPPER-LEVEL OUTFLOW HAS
ALSO WEAKENED, RESULTING IN AN INCREASINGLY UNFAVORABLE
ENVIRONMENT.

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

CURRENT STEERING MECHANISM: NORTHWEST PERIPHERY OF DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 43 KTS AT 122109Z
   CIMSS ADT: 32 KTS AT 122340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EASTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: NOW THAT THE SOUTHEASTERN RIDGE HAS ASSUMED
THE DOMINANT STEERING ROLE, TD 23W IS FORECAST TO CONTINUE TRACKING
NORTHEASTWARD THROUGH THE FORECAST PERIOD. THE SYSTEM, HAVING
WEAKENED SIGNIFICANTLY, IS NO LONGER EXPECTED TO BE ABLE TO MUSTER
THE STRENGTH TO OVERCOME THE PERSISTENT SHEAR, AND IS FORECAST TO
STEADILY BUT SLOWLY WEAKEN THROUGH THE FORECAST PERIOD. BRIEF
PERIODS DURING WHICH CONVECTION MAY FLARE UP AND APPEAR OMINOUS CAN
BE EXPECTED OVER THE NEXT 24 TO 36 HOURS, ESPECIALLY DURING DIURNAL
MAXIMUM, BUT THE SYSTEM IS NOT EXPECTED TO ACTUALLY INTENSIFY AFTER
THIS POINT. BY TAU 48 THE SYSTEM WILL BE NEARLY GONE, AND WILL BE
FULLY DISSIPATED NO LATER THAN TAU 72, IF NOT EARLIER. 

MODEL DISCUSSION: AS THE VORTEX CONTINUES TO WEAKEN AND BECOME
ELONGATED, MODEL TRACKERS ARE DIVERGING, WITH A 135NM SPREAD AT TAU
36 INCREASING TO 150NM AT TAU 72. THE JTWC FORECAST LIES ON THE
RIGHT EDGE OF THE GUIDANCE ENVELOPE THROUGH THE FORECAST PERIOD.
CONFIDENCE IS MEDIUM HOWEVER, IN LIGHT OF THE NEAR-TERM SPREAD IN
THE MODEL GUIDANCE. INTENSITY GUIDANCE IS MIXED, WITH ALL MODELS,
AND HWRF AND COAMPS IN PARTICULAR, INDICATING NEAR-TERM
INTENSIFICATION. THIS IS UNLIKELY IN LIGHT OF THE CONTINUING SHEAR
AND OVERALL WEAKENING OF THE SYSTEM, SO THE JTWC FORECAST LIES
BELOW ALL GUIDANCE THROUGH TAU THE FORECAST PERIOD, WITH MEDIUM
CONFIDENCE. 

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