WDPN31 PGTW 011500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (NYATOH) WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.2N 135.6E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 372 NM NORTH-NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A BROAD
SYSTEM WITH DEEP SUSTAINED CONVECTION OVER THE CENTER AND STRONG
RADIAL OUTFLOW. ALTHOUGH THE SYSTEM HAS NOT YET FORMED AN EYE, A
010912Z 91HZ SSMIS IMAGE DEPICTS A MICROWAVE EYE IN THE UPPER
LEVELS. THE INITIAL POSITION IS BASED ON THE PGTW POSITION FIX WHICH 
IS INLINE WITH AN EXTRAPOLATED POSITION BASED ON THE MICROWAVE EYE 
IN THE SSMIS IMAGE. THE INITIAL INTENSITY OF 65 KTS IS BASED ON THE 
PGTW CURRENT INTENSITY ESTIMATE OF T4.0. TROPICAL CYCLONE NYATOH IS 
CURRENTLY TRACKING THROUGH A VERY IDEAL ENVIRONMENT FOR FURTHER
INTENSIFICATION, WITH EXCEPTIONALLY HIGH OCEAN HEAT CONTENT, LOW
VERTICAL WINDS SHEAR, AND ROBUST RADIAL OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: THE SOUTHWESTERN EDGE OF THE
SUBTROPICAL RIDGE.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T4.5 - 77 KTS
   CIMSS ADT: 61 KTS AT 011140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

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: OVER THE NEXT 24 HOURS, TY 27W WILL REMAIN IN
A HIGHLY FAVORABLE ENVIRONMENT WITH LOW VERTICAL WIND SHEAR AND
HIGH OCEAN HEAT CONTENT AS IT CONTINUES TO TRACK AROUND THE WESTERN
EDGE OF THE SUBTROPICAL RIDGE. THE SYSTEM WILL UNDERGO A PERIOD OF
STEADY INTENSIFICATION UP AND WILL REACH ITS PEAK INTENSITY OF 90
KTS AROUND TAU 24, AT WHICH POINT THE FAVORABLE ENVIRONMENT WILL
BEGIN TO ERODE. BY TAU 36, RAPIDLY INCREASING VERTICAL WIND SHEAR
FROM A MID-LATITUDE TROUGH TO NORTH FOLLOWED DRY AIR ENTRAINMENT
WILL BEGIN TO WEAKEN THE SYSTEM AS IT ACCELERATES NORTHEASTWARD. BY
TAU 72, THE ADDITION OF COOL SEA SURFACE TEMPERATURES WILL BRING
THE INTENSITY DOWN TO 45 KTS. AROUND THIS SAME TIME, THE EXTREMELY
HIGH VERTICAL WIND SHEAR (40+ KTS) WILL DECOUPLE THE UPPER LEVELS
FROM THE LOW LEVEL VORTEX, WHICH WILL THEN FURTHER WEAKEN AND DRIFT
SOUTHWEST FOR THE REMAINDER OF THE FORECAST UNDER THE INFLUENCE OF
LOW LEVEL STEERING FEATURES AND EVENTUALLY DISSIPATE NO LATER THAN
TAU 120. 

MODEL DISCUSSION: FORECAST INTENSITY GUIDANCE IS IN GOOD AGREEMENT
IN REGARDS TO FORECAST INTENSITY TIMING AND TREND. ALL MODELS
DEPICT A PERIOD OF MODERATE TO STEADY INTENSIFICATION BEFORE A PEAK
INTENSITY AT TAU 24 WHICH IS THEN FOLLOWED BY A RAPID WEAKENING
TREND. THERE IS DISAGREEMENT IN REGARDS TO THE ACTUAL PEAK
INTENSITY WITH GFS ON THE LOW END PEAKING AT 75 KTS AND HWRF ON THE
HIGH END PEAKING AT 105 KTS. OVER THE PAST 24 HOURS, THE INTENSITY
TREND IN THE MODEL HAS REMAINED CONSISTENT, BUT THE OVERALL
CONSENSUS HAS DECREASE IN INTENSITY WITH LESS MODELS SUPPORTING
RAPID INTENSIFICATION. THE JTWC FORECAST IS CURRENTLY PLACED 5 KTS
HIGHER THAN CONSENSUS. FORECAST TRACK GUIDANCE IS GOOD AGREEMENT
FOR THE FIRST 24 HOURS OF THE FORECAST. FROM TAU 24 TO TAU 48,
CROSS-TRACK SPREAD REMAINS TIGHT BUT ALONG-TRACK SPREAD INCREASES
AS SOME MODELS BEGIN TO ACCELERATE THE SYSTEM NORTHEASTWARD. AFTER
TAU 72, THE MODELS ARE IN DISAGREEMENT AS TRACK UNCERTAINTY
INCREASES DUE TO POOR HANDLING TO THE DECOUPLING PROCESS. THERE IS
ESPECIALLY LOW CONFIDENCE IN THE FORECAST TRACK AFTER TAU 72 DUE TO
THE VARIOUS POSSIBILITIES IN HOW THE DECOUPLING WILL AFFECT WHERE
THE LOW LEVEL VORTEX TRACKS ONCE THE DECOUPLING IS COMPLETE.

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