WDPN31 PGTW 221500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 25W (TWENTYFIVE) 
WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.3N 118.9E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 657 NM EAST-NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 9 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS BROAD, 
SHALLOW BANDING WRAPPING INTO A RAGGED LOW-LEVEL CIRCULATION CENTER 
(LLCC) WITH FLARING, ISOLATED DEEP CONVECTION OVER THE NORTHERN 
QUADRANT. A 221149Z AMSU-B 89GHZ MICROWAVE IMAGE REVEALS A WEAKLY-
DEFINED LLCC WITH WEAK BANDING. THE INITIAL POSITION IS PLACED WITH 
MEDIUM CONFIDENCE BASED ON THE EIR IMAGERY. A 221200Z GFS SOUNDING 
THROUGH THE CENTER CONTINUES TO INDICATE A STABLE LOWER LAYER WITH AN 
INVERSION NEAR 850MB, WHICH MAKES SENSE CONSIDERING THE STABLE CLOUD 
TYPE ADVECTING INTO THE SYSTEM'S CORE. A 220945Z SMAP PASS SHOWED 
MAXIMUM WINDS OF 26-27 KNOTS OVER THE NORTHERN SEMICIRCLE BUT THESE 
WINDS WERE ISOLATED WITH SIGNIFICANTLY LOWER WINDS ELSEWHERE. SURFACE 
OBSERVATIONS FROM DONGSHA DAO (59792), APPROXIMATELY 125NM WEST-
NORTHWEST OF THE CENTER, INDICATE NORTHERLY WINDS AT 21 KNOTS AND SLP 
NEAR 1014MB. UPPER-LEVEL ANALYSIS INDICATES WEAK EQUATORWARD OUTFLOW 
AND LOW VERTICAL WIND SHEAR. ADDITIONALLY, THE LOW-LEVEL ENVIRONMENT 
REMAINS MARGINAL WITH STABLE CONDITIONS SO OVERALL CONDITIONS ARE 
ASSESSED AS MARGINAL.

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

CURRENT STEERING MECHANISM: LOW-LEVEL SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTH AND NORTHWEST.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   CIMSS ADT: 25 KTS AT 221140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK EQUATORWARD

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: TD 25 IS FORECAST TO TRACK WEST-SOUTHWESTWARD 
THROUGH TAU 12 BUT IS EXPECTED TO TURN SOUTHWESTWARD AS IT TRACKS 
WITHIN THE GENERAL LOW-LEVEL NORTHEASTERLY SURGE FLOW. TD 25W IS
STRUGGLING BUT IS EXPECTED TO MAINTAIN TD STRENGTH THROUGH TAU 24
WITH A STEADY WEAKENING TREND AND EVENTUAL DISSIPATION BY TAU 36.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
WITH A 40 TO 70NM SPREAD IN SOLUTIONS FROM TAU 24 TO TAU 36,
THEREFORE, THERE IS MEDIUM CONFIDENCE IN THE JTWC FORECAST TRACK.
RELIABLE INTENSITY GUIDANCE RANGES FROM A PEAK OF 25-33 KNOTS OVER
THE NEXT 24-36 HOURS THEN STEADY WEAKENING. HOWEVER, HWRF, WHICH 
INDICATES A PEAK OF 33 KNOTS AT TAU 36, ACTUALLY DISSIPATES THE 
SYSTEM WITHIN THE NEXT 24 HOURS AND DEVELOPS ANOTHER LOW PRESSURE 
AREA WITHIN THE SURGE FLOW NEAR 18N 112E. CONSEQUENTLY, THE JTWC 
INTENSITY FORECAST IS ON THE LOWER SIDE OF THE GUIDANCE ENVELOPE WITH 
MEDIUM CONFIDENCE.

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