WDPN31 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (NALGAE) WARNING NR 
027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.5N 114.8E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 58 NM SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A RAPIDLY
WEAKENING SYSTEM WITH THE SHALLOW AND IRREGULAR CENTRAL CONVECTION
SHEARED NM NORTHEASTWARD, PARTLY EXPOSING A RAGGED LOW-LEVEL
CIRCULATION (LLC) THAT IS TRACKING DEEPER INTO THE COLD NORTHEASTERLY 
WIND SURGE THAT IS FUNNELING IN FROM THE TAIWAN STRAIT INTO THE SOUTH 
CHINA SEA (SCS). THE SURGE IS EVIDENCED BY LOW LEVEL STRATOCUMULUS 
LINES STREAMING SOUTHWESTWARD IN CONTRA-FLOW WITH THE UPPER-LEVEL 
CIRRI STREAKS CAUGHT IN THE SOUTHWESTERLY JET STREAM THAT IS 
PROVIDING STRONG POLEWARD OUTFLOW TO THE WEAKENING CONVECTION. THE 
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A DEFINED 
LLC IN THE COMPOSITE RADAR LOOP FROM HONG KONG. THE INITIAL INTENSITY 
IS DEDUCED FROM THE 020958Z SMAP TO ACCOUNT FOR WEAKENING BUT STILL 
HELD SLIGHTLY HIGHER THAN AGENCY AND AUTOMATED DVORAK ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE AND SYNOPTIC OBSERVATIONS.

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


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   CIMSS ADT: 29 KTS AT 020840Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 24-25 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM NALGAE WILL TURN MORE
NORTHWESTWARD THEN SOUTHWESTWARD AS AN EXTENSION OF A SECONDARY STR 
TO THE WEST-NORTHWEST ASSUMES STEERING. THE UNFAVORABLE ENVIRONMENT, 
MAINLY DUE TO THE COLD SURGE, COOLING SST, AND INCREASING VWS, WILL 
CONTINUE TO RAPIDLY WEAKEN THE SYSTEM TO DISSIPATION BY TAU 36, 
POSSIBLY SOONER.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT UP TO TAU
12 THEN SPREAD OUT TO OVER 100NM BY TAU 36 AS THE MODELS LOSE THE
VORTEX, LENDING AN OVERALL MEDIUM CONFIDENCE TO THE JTWC TRACK
FORECAST. 

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