WDPN31 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 25W (TWENTYFIVE) 
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.5N 126.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 372 NM SOUTH-SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES THE
SYSTEM IS DISORGANIZED WITH A LARGE CLUSTER OF PERSISTENT DEEP
CONVECTION EXTENDING OVER THE SOUTHWESTERN SEMICIRCLE OF A BROAD
LOW-LEVEL CIRCULATION. ADDITIONALLY, WATER VAPOR IMAGERY INDICATES
A RELATIVELY DRY STABLE AIR MASS TO THE NORTH, WITH MODERATE
EQUATORWARD OUTFLOW TO THE SOUTH OF THE SYSTEM. THESE ENVIRONMENTAL
FACTORS CONTINUE TO PREVENT RAPID CONSOLIDATION AND STRENGTHENING.
THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
ANIMATED EIR, ALONG WITH AN EARLIER 201324Z PARTIAL ASCAT-B, WHICH
SHOWS AN ELONGATED HIGHLY ASYMMETRICAL CIRCULATION, WITH 25-30
KNOTS ON THE NORTHEASTERN PERIPHERY, WITH LIGHTER WINDS ON THE
SOUTHERN PERIPHERY. THE INITIAL INTENSITY OF 30 KNOTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE EARLIER ASCAT-B ALONG WITH A
COMBINATION OF OBJECTIVE AND SUBJECTIVE DVORAK INTENSITY ESTIMATES
WHICH ARE ON THE HIGH END OF INTENSITY ESTIMATES. ENVIRONMENTAL
CONDITIONS ARE MARGINALLY FAVORABLE WITH DRY STABLE AIR TO THE NORTH, 
MODERATE EQUATORWARD OUTFLOW, WARM (29-30C) SEA SURFACE TEMPERATURES 
(SSTS), AND LOW (0-5KTS) VERTICAL WIND SHEAR (VWS).

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

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED OVER TAIWAN. 


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.0 - 25 KTS
   CIMSS SATCON: 38 KTS AT 201333Z
   CIMSS ADT: 39 KTS AT 201740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY STABLE AIR ON THE NORTHWESTERN PERIPHERY OF
CIRCULATION  

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   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: OVER THE PAST SIX HOURS TD 25W CONTINUES TO
TRACK GENERALLY WESTWARD ALONG THE SOUTHEASTERN PERIPHERY OF A
DEEP-LAYER SUBTROPICAL RIDGE (STR) POSITIONED OVER TAIWAN. THIS
GENERAL WESTWARD TRACK WILL CONTINUE THROUGH TAU 24. THEN BY TAU
36, THE SYSTEM WILL PASS THROUGH THE LUZON STRAIGHT WITH A SLIGHT
TRACK POLEWARD AS A WEAK TROUGH PASSES TO THE NORTH THAT WILL
INDUCE A WEAKNESS WITHIN THE STEERING RIDGE. BY TAU 48, 25W WILL
TRANSIT INTO THE SOUTH CHINA SEA AND REACH AN INFLECTION POINT
WHEREBY THE PRIMARY STEERING MECHANISM BECOMES A DEEP LAYER RIDGE
OVER EAST CHINA. THIS STEERING MECHANISM WILL THEN STEER THE SYSTEM
GENERALLY SOUTHWESTWARD THROUGH THE REMAINED OF THE FORECAST
PERIOD. TD 25W WILL SLOWLY INTENSIFY THROUGH THE NEXT 24 HOURS DUE
TO THE INITIAL HIGHLY ASYMMETRICAL LLCC ALONG WITH THE DRY STABLE
AIR OVER THE NORTHERN PERIPHERY. HOWEVER, ENVIRONMENTAL CONDITIONS
ARE FORECAST TO IMPROVE BETWEEN TAU 36 AND TAU 72, AS THE SYSTEM
WILL MOVE INTO A MORE CONDUCIVE ENVIRONMENTAL WITH IMPROVED 
UPPER-LEVEL OUTFLOW WHICH WILL ALLOW FOR A FAST INTENSIFICATION
PERIOD. AFTER TAU 72, DECREASING SEA SURFACE TEMPERATURES (SSTS)
LEFT IN THE WAKE OF TY 23W ALONG WITH UPPER-LEVEL CONVERGENT
EASTERLY FLOW WILL RESULT IN STEADY WEAKENING THROUGH TAU 120.  

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE REMAINS IS IN GOOD
AGREEMENT WITH THE EXCEPTION OF COTI AND NAVGEM WHICH REMAIN THE
NORTHERN OUTLIERS THROUGH TAU 72. BETWEEN TAU 96 AND TAU 120
UNCERTAINLY IN TRACK GUIDANCE INCREASE TO A 370NM CROSS-TRACK
SPREAD. ADDITIONALLY, THE GFS ENSEMBLE (GEFS) SOLUTIONS SUPPORT THE
JTWC FORECAST TRACK THROUGH TAU 72, WITH INCREASING CROSS-TRACK
SPREAD BY TAU 120. THEREFORE, THE JTWC FORECAST TRACK IS POSITIONED
CLOSE TO THE MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE. THE
INTENSITY GUIDANCE IS IN FAIR AGREEMENT AND SUPPORTS AN 
INTENSIFICATION PHASE THROUGH TAU 72 WITH HWRF INDICATING A PEAK 
INTENSITY NEAR 80 KNOTS AND COAMPS-TC (GFS VERSION) INDICTING A PEAK 
INTENSITY OF 60 KNOTS, WHICH IS MORE INLINE WITH THE INTENSITY 
CONSENSUS PEAK OF 60 KNOTS. COMAMPS-TC EPS INDICATES HIGH PROBABILITY 
OF MODERATE INTENSIFICATION AND A 70 PERCENT CHANCE OF RAPID 
INTENSIFICATION (RI) BETWEEN TAU 48 AND TAU 72. WHEREAS THE GEFS SHOWS 
A MORE MODERATE INTENSIFICATION FROM TAU 48 THROUGH TAU 72 GIVEN THE 
UNCERTAINLY IN THE INTENSITY DURING THIS TIME-FRAME, THE JTWC FORECAST 
INTENSITY IS PLACED WITH LOW CONFIDENCE. 

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