WDPN31 PGTW 232100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 12W (TWELVE) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.2N 144.1E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 32 NM WEST-SOUTHWEST OF NAVSTA GUAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CONSOLIDATING, PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC) WITH POCKETS OF DEEP CONVECTION WITHIN THE SOUTHERN
PERIPHERY. A 231607Z AMSR2 89 GHZ MICROWAVE IMAGE REVEALED DEFINED
LOW-LEVEL CLOUDS WRAPPING INTO THE ASSESSED CENTER AND THE DEEP
CONVECTION CONFINED TO THE SOUTHERN PORTION OF THE CIRCULATION.
ENVIRONMENTAL ANALYSIS INDICATES THAT 12W IS IN A MARGINAL
ENVIRONMENT CHARACTERIZED BY MODERATE EQUATORWARD OUTFLOW ALOFT,
HIGH (25-30 KTS) NORTHERLY VERTICAL WIND SHEAR, AND WARM (29-30 C)
SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE BASED ON THE MENTIONED AMSR2 MICROWAVE IMAGE AND
ANIMATED EIR SATELLITE IMAGERY. THE INITIAL INTENSITY OF 25 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON T1.0 FIXES FROM PGTW AND
KNES AND AN 1800Z CIMSS DPRINT ESTIMATE OF 21 KTS. ADDITIONALLY, A
231159Z METOP-C ASCAT IMAGE REVEALED A SWATH OF 20-25 KTS WITHIN
THE SOUTHERN SEMICIRCLE, DISPLACED ABOUT 80 NM TO THE SOUTH OF THE
LLCC.

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

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT WITH NO CLEAR
STEERING MECHANISM ACTING ON THE SYSTEM. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.0 - 25 KTS
   KNES: T1.0 - 25 KTS
   CIMSS DPRINT: 21 KTS AT 231800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TD 12W IS FORECAST TO BEGIN TRACKING NORTHWARD
AS RIDGING BUILDS IN TO THE EAST OF THE VORTEX OVER THE NEXT 48
HOURS. THIS NORTHWARD TRACK IS FORECAST TO PERSIST THROUGH TAU 96 AS
12W RIDES ALONG THE WESTERN PERIPHERY OF THE RIDGE. NEAR TAU 96, A
SUBTROPICAL RIDGE CENTERED OVER SOUTHERN HONSHU WILL BEGIN TO
INTERACT WITH THE VORTEX AND WILL PULL 12W NORTHWESTWARD THROUGH
TAU 120. REGARDING INTENSITY, 12W IS FORECAST TO STEADILY INTENSIFY
OVER THE NEXT 72 HOURS. HOWEVER, THE ENVIRONMENT WILL BE COMPLEX,
WITH ENVIRONMENTAL FACTORS FIGHTING AGAINST EACH OTHER FOR THE
DEVELOPMENT OF 12W. THROUGH TAU 48, THE WIND FIELD WILL CONTINUE TO
CONSOLIDATE AND WILL ALLOW FOR INTENSIFICATION OF THE SYSTEM. 
AFTER TAU 48, AN UPPER-LEVEL TROUGH WILL SET UP TO THE NORTHEAST OF
THE SYSTEM, DRASTICALLY ENHANCING EASTWARD AND EQUATORWARD OUTFLOW.
AT THE SAME TIME, NORTHERLY VERTICAL WIND SHEAR WILL RISE TO ABOVE
40 KTS. THE RESULT OF THESE TWO FACTORS IS FORECAST TO RESULT IN
SLIGHT INTENSIFICATION FROM 45 KTS AT TAU 48 TO 60 KTS AT TAU 96.
AFTER TAU 96, DRY AIR ENTRAINMENT IS EXPECTED TO MARKEDLY INCREASE
AS THE VORTEX BEGINS TO INTERACT WITH A TROPICAL UPPER TROPOSPHERIC
TROUGH (TUTT) CELL THAT FORMS SOUTH OF HONSHU. THIS WILL CAUSE 12W
TO STOP INTENSIFYING THROUGH THE REMAINDER OF THE FORECAST PERIOD.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN MODERATE
AGREEMENT THROUGH TAU 72 WITH THE PRIMARY OUTLIERS BEING THE GFS
AND THE GFS ENSEMBLE MEAN, WHICH ARE ABOUT 160 NM FURTHER NORTH AT
TAU 72 THAN THE BULK OF GUIDANCE. AFTER TAU 72, CROSS-TRACK SPREAD
INCREASES SIGNIFICANTLY WITH UKMET AND GALWEM BOTH TRACKING THE
SYSTEM NORTH-NORTHEAST RATHER THAN NORTH-NORTHWEST. THE JTWC TRACK
FORECAST IS PLACED IN LINE WITH THE MULTI-MODEL CONSENSUS (SLIGHTLY
SLOWER TO OFFSET GFS) THROUGH TAU 96 AND THEN CLOSER TO THE ECMWF
ENSEMBLE MEAN THROUGH TAU 120. OVERALL, THERE IS MEDIUM CONFIDENCE
IN THE JTWC TRACK FORECAST THOUGH TAU 72 AND THEN LOW CONFIDENCE
THEREAFTER. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72
WITH ALL MODELS SUGGESTING STEADY INTENSIFICATION THROUGH THAT
TIME. AFTER TAU 72, HWRF AND GFS BOTH SUGGEST WEAKENING THROUGH TAU
120 WHILE HAFS-A SUGGESTS FURTHER INTENSIFICATION. THE JTWC
INTENSITY FORECAST IS PLACED CLOSE TO CONSENSUS THROUGH TAU 96 AND
THEN HALTS THE INTENSIFICATION THROUGH TAU 120 DUE TO THE EXPECTED
DEGRADED ENVIRONMENT AS THE SYSTEM INTERACTS WITH THE TUTT CELL.

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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