WDPN31 PGTW 300900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (NYATOH) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.9N 138.1E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 200 NM NORTH-NORTHWEST OF ULITHI
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY
CONSOLIDATING SYSTEM WITH ROBUST RADIAL OUTFLOW AND A CLEARLY
DEFINED LOW LEVEL CIRCULATION CENTER WHICH LENDS HIGH CONFIDENCE TO
THE INITIAL POSITION. THE INITIAL INTENSITY OF 40 KTS IS HEDGED
SLIGHTLY HIGHER THAN PGTW AND KNES DVORAK ESTIMATES TO ACCOUNT FOR 
THE POSSIBLE START OF A PERIOD OF RAPID INTENSIFICATION WHICH WILL BE
FURTHER DISCUSSED IN THE FORECAST DISCUSSION.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: THE DEEP LAYERED SUBTROPICAL RIDGE TO
THE NORTHWEST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 50 KTS AT 300413Z
   CIMSS ADT: 55 KTS AT 300540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

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: TROPICAL STORM 27W WILL TRACK NORTHWESTWARD
OVER THE NEXT 24 HOURS BEFORE BEGINNING A MORE NORTHWARD TRACK AS
IT ROUNDS THE SUBTROPICAL RIDGE AXIS FROM TAU 36 TO TAU 48. AFTER
TAU 48, THE SYSTEM WILL BEGIN TO ACCELERATE NORTHEASTWARD UNDER THE
INFLUENCE OF A DEEP MID-LATITUDE TROUGH PASSING TO THE NORTH. DUE
TO INCREASINGLY ROBUST OUTFLOW PAIRED WITH HIGHLY FAVORABLE OCEAN
HEAT CONTENT AND LOW VERTICAL WIND SHEAR, TS 27W WILL UNDERGO A
PERIOD OF RAPID INTENSIFICATION FROM TAU 6 TO TAU 48. THE CURRENT
FORECAST PEAKS THE INTENSITY AT 100 KTS AT TAU 48, BUT IT IS LIKELY
TO REACH 110 KTS SOMETIME AROUND TAU 60 BEFORE INCREASING VERTICAL
WIND SHEAR FROM THE MID-LATITUDE TROUGH TO THE NORTH BEGINS TO
WEAKEN THE SYSTEM TO 95 KTS BY TAU 72. IN ADDITION TO WEAKENING THE
SYSTEM, THE VERTICAL WIND SHEAR FROM THE MID-LATITUDE TROUGH IS
EXPECTED INITIATE A DECOUPLING PROCESS OF THE CIRCULATION. THIS IS 
EXPECTED TO OCCUR AFTER TAU 96 WITH THE REMAINING LOW LEVEL 
CIRCULATION, NOW UNDER THE INFLUENCE OF LOW LEVEL STEERING FEATURES, 
BEING DRIVEN SOUTHWESTWARD. 

MODEL DISCUSSION: IN REGARDS TO FORECAST INTENSITY, BOTH
DETERMINISTIC AND ENSEMBLE MODELS ARE GENERALLY IN GOOD AGREEMENT
AS FAR A THE TREND OF INTENSIFICATION. LATEST RUNS DEPICT A PERIOD
OF MODERATE TO RAPID INTENSIFICATION UP TO TAU 48 WITH PEAK
INTENSITY AROUND TAU 60 AND A MODERATE TO RAPID WEAKENING FOR THE
REMAINDER OF THE FORECAST. THE RANGE OF PEAK INTENSITY VARIES WITH
GFS PEAKING AT ABOUT 80 KTS AND CTCI PEAKING NEAR 120 KTS. THE
FORECAST INTENSITY IS THEREFORE BASED OFF OF THE CONSENSUS. IN 
REGARDS TO FORECAST TRACK, THE MODELS SPLIT BETWEEN TWO POSSIBLE 
SCENARIOS. THE GFS DETERMINISTIC, GFS ENSEMBLE, EGRR, AND AFUM 
DEPICT A DECOUPLING SCENARIO AROUND TAU 96, WHICH THE FORECAST TRACK
CURRENTLY REFLECTS. ALTERNATIVELY, THE ECMWF DETERMINISTIC, ECMWF
ENSEMBLE, AND NVGM DEPICT A SCENARIO WHERE THE SYSTEM IS PULLED
NORTHEASTWARD AFTER TAU 96 IN THE WAKE OF THE MID-LATITUDE TROUGH
AND DISSIPATES OR UNDERGOES EXTRATROPICAL TRANSITION.     

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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