WDPN31 PGTW 010900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (NYATOH) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.4N 135.9E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 321 NM NORTH-NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD
SYSTEM WITH DEEP SUSTAINED CONVECTION AND A DRY AIR SLOT WRAPPING
INTO THE SOUTHERN SEMI-CIRCLE OF THE CIRCULATION. THE INITIAL
POSITION IS BASED ON THE PGTW POSITION FIX WHICH IS INLINE WITH AN
EXTRAPOLATED POSITION BASED ON BANDING IN A 010408 AMSR2 IMAGE. THE
INITIAL INTENSITY OF 60 KTS IS AVERAGED BY ALL CURRENT AGENCY
AND AUTOMATED INTENSITY ESTIMATES WHICH ARE IN RELATIVELY GOOD
AGREEMENT. TROPICAL CYCLONE NYATOH IS CURRENTLY TRACKING THROUGH A
NEARLY IDEAL ENVIRONMENT FOR FURTHER INTENSIFICATION, WITH
EXCEPTIONALLY HIGH OCEAN HEAT CONTENT, LOW VERTICAL WIND 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: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 59 KTS AT 010355Z
   CIMSS ADT: 59 KTS AT 010540Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 36 HOURS, TS 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
RAPID INTENSIFICATION UP TO TAU 24 AND WILL REACH ITS PEAK
INTENSITY OF 100 KTS AROUND TAU 36, AT WHICH POINT THE FAVORABLE
ENVIRONMENT WILL BEGIN TO ERODE. A COMBINATION OF INCREASING
VERTICAL WIND SHEAR FROM A MID-LATITUDE TROUGH TO NORTH AND 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 60 KTS. AROUND THIS
SAME TIME, THE HIGH VERTICAL WIND SHEAR (40+ KTS) WILL DECOUPLE THE
LOW LEVEL VORTEX, WHICH WILL FURTHER WEAKEN AND DRIFT SOUTHWEST FOR
THE REMAINDER OF THE FORECAST UNDER THE INFLUENCE OF LOW LEVEL
STEERING FEATURES. 

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 RAPID INTENSIFICATION BEFORE A PEAK
INTENSITY AROUND TAU 36 WHICH IS THEN FOLLOWED BY A MODERATE TO
RAPID WEAKENING TREND. HOWEVER, 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 115 KTS. THE JTWC FORECAST IS
PLACED CLOSE TO THE CONSENSUS WHICH HAS BEEN FAIRLY CONSISTENT
OVER THE PAST 24 HOURS. 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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