WDPN31 PGTW 190300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (NOKAEN) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.6N 126.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 340 NM EAST-NORTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC) ASSOCIATED WITH
TROPICAL STORM (TS) 01W (NOKAEN). THE SYSTEM IS STILL BETWEEN
IMPACTS OF MARGINALLY FAVORABLE AND STRUCTURALLY DEGRADING
ENVIRONMENTAL CHARACTERISTICS. THE INFLUENCE OF A PERVASIVE,
DEEP-LAYER DRY AIR MASS AND A LOW-TO-MODERATE (15-20 KTS) VERTICAL
WIND SHEAR (VWS) ARE OFFSET BY WARM (26-27 C) SEA SURFACE
TEMPERATURES (SST) AND GOOD POLEWARD OUTFLOW ALOFT. IN THE
PRECEDING HOURS CONVECTIVE BURSTS HAVE MATERIALIZED IN PROXIMITY TO
THE VORTEX CORE, COMPLEMENTED BY MORE ORGANIZED DEEP CONVECTION
THROUGHOUT THE FEEDING BANDS. THEREFORE, THE OVERALL SYNOPTIC
ENVIRONMENT REMAINS MARGINALLY FAVORABLE. THE INITIAL POSITION IS
DETERMINED WITH HIGH CONFIDENCE, DERIVED FROM PARTIALLY EXPOSED
LLCC PRESENT IN THE VISIBLE IMAGERY LOOP. A MEDIUM CONFIDENCE
ASSESSMENT IS PLACED ON THE INITIAL INTENSITY OF 35 KTS, PREDICATED
ON THE RECENT DEVELOPMENT OF CENTRAL CONVECTION VIEWED IN
CONJUNCTION WITH SUBJECTIVE DVORAK CLASSIFICATIONS AND OBJECTIVE
SATELLITE-BASED INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) CENTERED TO THE
EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T1.5 - 25 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 34 KTS AT 182214Z
   CIMSS ADT: 33 KTS AT 182040Z
   CIMSS AIDT: 32 KTS AT 182040Z
   CIMSS D-MINT: 26 KTS AT 182213Z
   CIMSS D-PRINT: 29 KTS AT 190020Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 01W IS FORECAST TO NAVIGATE THE
NORTHWESTERN PERIPHERY OF THE EASTERN SUBTROPICAL RIDGE (STR)
THROUGH APPROXIMATELY TAU 36. SUBSEQUENTLY, A LARGE-SCALE PATTERN
SHIFT IS ANTICIPATED, CHARACTERIZED BY THE RETROGRADE MOTION AND
ATTENUATION OF THIS STEERING RIDGE, COINCIDENT WITH THE EASTWARD
EXPANSION OF A SEPARATE STR DEVELOPING TO THE WEST. THIS DEFINITIVE
TRANSITION IN THE DEEP-LAYER STEERING REGIME IS EXPECTED TO INDUCE
AN EQUATORWARD DEFLECTION IN THE TRAJECTORY OF TS 01W SHORTLY AFTER
TAU 36, FORCING IT ONTO THE EASTERN FLANK OF THE NOW-DOMINANT
WESTERN STR. WITH RESPECT TO THE INTENSITY FORECAST, A RELAXATION
OF THE VWS, COUPLED WITH THE PERSISTENT POLEWARD OUTFLOW WILL
RESULT IN MODEST INTENSIFICATION PHASE TO 40 KTS UNTIL TAU 48.
SHORTLY THEREAFTER, THE COMBINED INFLUENCE OF THE DEEP-LAYER DRY
AIR, A SIGNIFICANT INCREASE OF THE VWS, AND PERSISTENT NORTHEASTERLY 
LOW-LEVEL SURGE EVENT TO THE NORTHWEST WILL INITIATE A TERMINAL 
WEAKENING TREND, WITH COMPLETE DISSIPATION OF THE CYCLONE PROJECTED 
AROUND OR SHORTLY AFTER TAU 72.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE REMAINS IN FAIR
AGREEMENT ONLY FOR THE INITIAL 24 HOURS, REFLECTED BY A CROSS-TRACK
SPREAD OF 22 NM AT THAT TAU. HOWEVER, THE GUIDANCE ENVELOPE
DIVERGES SUBSTANTIALLY THEREAFTER, REACHING A 280 NM SPREAD AT TAU
72, WHICH NECESSITATES A LOW CONFIDENCE ASSESSMENT FOR THE
LONG-TERM TRACK. NAVGEM PROJECTS THE SHARPEST AND RAPID
RECURVATURE, WHILE THE ECMWF SUITE DEPICTS A MORE GRADUAL AND BROADER
TURN SOUTHWARD. THE OFFICIAL JTWC TRACK IS POSITIONED WITH MEDIUM
CONFIDENCE AND CLOSE TO THE MULTI-MODEL CONSENSUS, ALIGNED SLIGHTLY
TOWARDS THE OUTSIDE OF THE MEAN PROJECTED TURN. THE NUMERICAL MODEL
INTENSITY GUIDANCE SUITE SHOWS A MODERATE CONSENSUS THROUGHOUT THE
FORECAST PERIOD, WITH ALL AVAILABLE SOLUTIONS INDICATING AN INITIAL
INTENSIFICATION TO 40 KTS, FOLLOWED BY A STEADY DECAY BEGINNING
BETWEEN TAUS 36 AND 48. THE SPREAD WITHIN THE INTENSITY ENVELOPE
DURING THE LATTER PHASE IS APPROXIMATELY 20 KTS, INTRODUCING SOME
UNCERTAINTY REGARDING THE PRECISE TIMING OF DISSIPATION.
CONSEQUENTLY, THE INTENSITY FORECAST IS ASSIGNED MEDIUM CONFIDENCE.


FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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