WDPN32 PGTW 161500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NAMTHEUN) WARNING 
NR 027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.8N 166.0E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 751 NM NORTH OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AFTER BRIEFLY PEAKING AT TYPHOON STRENGTH AT 160600Z, ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES THAT CLOUD TOPS
HAVE WARMED AND THE DEEP CONVECTIVE STRUCTURE HAS WEAKENED
SIGNIFICANTLY. A 161037Z AMSU 89GHZ IMAGE, HOWEVER, REVEALS
CONVECTIVE BANDING WRAPPING TIGHTLY INTO A DEFINED LOW-LEVEL
CIRCULATION CENTER, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH
CONFIDENCE. ENVIRONMENTAL CONDITIONS ARE NOW MARGINALLY FAVORABLE
DUE TO THE COOLING SEA SURFACE TEMPERATURES AND MID- TO UPPER-LEVEL
DRY AIR ENTRAINMENT. HOWEVER, VERTICAL WIND SHEAR (VWS) REMAINS LOW
WITH MODERATE OUTFLOW. THE INITIAL INTENSITY OF 60 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON AN AVERAGE OF THE PGTW AND KNES
CURRENT INTENSITY ESTIMATES AS WELL AS THE UW-CIMSS ADT ESTIMATE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTH-SOUTHWEST TO NORTH-NORTHEAST
ORIENTED SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 75 KTS AT 160757Z
   CIMSS ADT: 59 KTS AT 161340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT OVER THE WESTERN SEMICIRCLE.

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 23W IS EXPECTED TO ACCELERATE NORTH-
NORTHEASTWARD TO NORTHWARD THROUGH TAU 36 ALONG THE WESTERN
PERIPHERY OF THE STR. SIGNIFICANT WEAKENING WILL OCCUR AS SEA
SURFACE TEMPERATURES RAPIDLY COOL FROM 26C TO 21C BY TAU 36.
ADDITIONALLY, VWS WILL INCREASE TO MODERATE LEVELS AS THE SYSTEM
BEGINS EXTRA-TROPICAL TRANSITION (ETT) AND INTERACTS WITH THE
BAROCLINIC ZONE NEAR TAU 24. AFTER TAU 36, TS 23W WILL RECURVE
NORTHEASTWARD AS IT ROUNDS THE NORTHWEST PERIPHERY OF THE STR.
FURTHER WEAKENING WILL OCCUR AS SEA SURFACE TEMPERATURES COOL
FURTHER TO 16C, VWS INCREASES TO 30-35 KNOTS AND ETT COMPLETES. TS
23W SHOULD GAIN FRONTAL CHARACTERISTICS BY TAU 48 AS IT BEGINS TO
TRACK NEAR JET-STRENGTH UPPER LEVEL WINDS.   

MODEL DISCUSSION: WITH THE EXCEPTION OF AFUM, NUMERICAL MODEL
GUIDANCE IS IN TIGHT AGREEMENT THROUGH THE FORECAST PERIOD WITH A
65NM SPREAD IN SOLUTIONS AT TAU 48. INTENSITY GUIDANCE IS ALSO IN
GOOD AGREEMENT AND SUPPORTS THE STEADY WEAKENING TREND. THEREFORE,
CONFIDENCE IN THE JTWC TRACK AND INTENSITY FORECAST IS HIGH.  

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