WDPN31 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (NALGAE)      
WARNING NR 025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.5N 115.2E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 122 NM SOUTH-SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY
DETERIORATING SYSTEM WITH LOW-LEVEL CLOUD BANDS WRAPPING INTO AN
EXPOSED, WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE MSI. A
012229Z SSMIS 91GHZ COLOR COMPOSITE MICROWAVE IMAGE REVEALS TIGHTLY
WRAPPED SHALLOW BANDING WRAPPING INTO THE LLCC WITH DISORGANIZED,
ISOLATED DEEP CONVECTION SHEARED TO THE NORTH. TS 26W IS LOCATED
UNDER UPPER-LEVEL SOUTHWESTERLY FLOW WITH LOW TO MODERATE VERTICAL 
WIND SHEAR (VWS). SST VALUES ACROSS THE REGION ARE MARGINAL AT 25-
26C. ADDITIONALLY, THERE IS SIGNIFICANT DRY AIR PRESENT OVER 
SOUTHEAST CHINA, WHICH IS NOW ENTRAINING INTO THE SOUTHERN PERIPHERY 
OF THE SYSTEM. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH 
MEDIUM CONFIDENCE BASED ON THE PGTW, RJTD DVORAK ESTIMATES AND THE 
CIMSS ADT ESTIMATE. ADDITIONALLY, A 020000Z SHIP OBSERVATION, 
APPROXIMATELY 137NM NNE OF THE CENTER, INDICATES 52 KNOT WINDS.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T4.0 - 65 KTS
   CIMSS ADT: 51 KTS AT 012340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 26W IS TRACKING SLOWLY NORTH-NORTHWESTWARD
DUE TO THE COMBINED STEERING INFLUENCE OF A STR POSITIONED TO THE
EAST AND ANOTHER BROADER STR POSITIONED TO THE NORTH. THE SYSTEM IS
EXPECTED TO TURN WESTWARD THEN WEST-SOUTHWESTWARD AFTER TAU 24 AS
THE STR POSITIONED OVER CHINA BECOMES THE DOMINANT STEERING 
INFLUENCE. DUE TO THE MARGINAL CONDITIONS, PARTICULARLY DRY AIR 
ENTRAINMENT AND FRICTIONAL EFFECTS OVER LAND, TS 26W WILL STEADILY 
WEAKEN WITH DISSIPATION ANTICIPATED NO LATER THAN TAU 48.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN FAIR AGREEMENT 
THEREFORE THERE IS MEDIUM OVERALL CONFIDENCE IN THE JTWC FORECAST 
TRACK. THE 011800Z ECMWF (EPS) AND GFS (GEFS) ENSEMBLES ARE ALSO IN 
FAIR AGREEMENT AND SUPPORT THE JTWC TRACK PHILOSOPHY. ALL ENSEMBLE 
SOLUTIONS INDICATE STEADY WEAKENING WITH A WEAK 20-25 KNOT SYSTEM 
TRACKING ALONG THE SOUTHERN COAST OF CHINA THEN FURTHER WEAKENING AND 
EVENTUAL DISSIPATION.

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