WDPN31 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (NALGAE)       
WARNING NR 024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.2N 115.4E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 143 NM SOUTH-SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS RAPIDLY
WEAKENING CORE CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION
CENTER (LLCC). A 011828Z ATMS 88.2GHZ MICROWAVE IMAGE REVEALS
LIMITED DEEP CONVECTION SHEARED NORTH OF A PARTIALLY EXPOSED LLCC,
WHICH IS LOCATED ALONG THE SOUTHERN EDGE OF THE DEEP CONVECTION. 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 POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON EIR AND THE ATMS MICROWAVE IMAGE.
THE INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE PGTW, RJTD DVORAK ESTIMATES AND THE CIMSS ADT
ESTIMATE.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK ADJUSTED USING
SCATTEROMETER DATA AND SHIP OBSERVATIONS   

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   KNES: T4.0 - 65 KTS
   CIMSS ADT: 55 KTS AT 011740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 72.  

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN FAIR
AGREEMENT WITH AN 80-100NM SPREAD IN SOLUTIONS FROM TAU 24 TO TAU
72, THEREFORE, THERE IS MEDIUM OVERALL CONFIDENCE IN THE JTWC
FORECAST TRACK. THE 011200Z 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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