WDPN31 PGTW 182100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01W (NOKAEN) WARNING 
NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.1N 125.7E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 286 NM EAST-NORTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A MAINLY
OBSCURED LOW-LEVEL CIRCULATION CENTER ASSOCIATED WITH TROPICAL
DEPRESSION (TD) 01W (NOKAEN). THE SYSTEM HAS BEEN STRUGGLING TO
MAINTAIN ITS STRUCTURE DUE TO SIGNIFICANT AMOUNT OF DRY AIR
SURROUNDING IT, AS WELL AS LOW TO MODERATE (15-20 KTS) VERTICAL
WIND SHEAR (VWS). OVER THE LAST FEW HOURS SOME CENTRAL CONVECTION
HAS DEVELOPED, ALONG WITH A PERIPHERAL DEEP CONVECTION PRIMARILY
THROUGHOUT THE NORTHERN SEMICIRCLE. THIS WAS ELEVATED BY A ROBUST
POLEWARD OUTFLOW CHANNEL. OTHER ENVIRONMENTAL PARAMETER RESULTING
IN MARGINALLY FAVORABLE OVERALL CONDITIONS IS WARM (26-27 C) SEA
SURFACE TEMPERATURE (SST). THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE BASED ON LOW-LEVEL CLOUD TRACING CONSISTENT WITH
THE EXTRAPOLATION FROM A 181557Z OCEANSAT-3 IMAGE DEPICTING AN 
IDENTIFIABLE AREA OF CALMER WINDS. THE INITIAL INTENSITY OF 30 KTS IS 
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE RECENTLY DEVELOPING 
CENTRAL CONVECTION IN CONJUNCTION WITH THE SUBJECTIVE DVORAK AND 
OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 33 KTS AT 181730Z
   CIMSS AIDT: 31 KTS AT 181900Z
   CIMSS D-MINT: 22 KTS AT 181701Z
   CIMSS D-PRINT: 25 KTS AT 181830Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TD 01W IS PROJECTED TO TRANSIT THE
NORTHWESTERN PERIPHERY OF THE EASTERN STR THROUGH TAU 36. A
SYNOPTIC PATTERN EVOLUTION IS ANTICIPATED SUBSEQUENT TO THAT TIME,
CHARACTERIZED BY THE EASTWARD RETREAT AND ATTENUATION OF THIS
STEERING RIDGE, OCCURRING IN CONCERT WITH THE ZONAL EXPANSION OF A
SEPARATE STR DEVELOPING TO THE WEST OF THE SYSTEM. THIS FUNDAMENTAL
SHIFT IN THE DEEP-LAYER STEERING REGIME IS EXPECTED TO INDUCE AN
EQUATORWARD DEFLECTION IN THE TRAJECTORY OF TD 01W AFTER TAU 36,
FORCING IT ONTO THE EASTERN FLANK OF THE NOW-ASCENDANT WESTERN STR.
ON THE INTENSITY FORECAST, SLIGHT DECREASE IN VWS COMBINED WITH
GOOD POLEWARD OUTFLOW WILL RESULT IN MINOR INTENSIFICATION TO 40
KTS BETWEEN TAUS 36 AND 48. SHORTLY AFTER, THE PRESENCE OF A
DEEP-LAYER, DRY AIR MASS SURROUNDING THE VORTEX, COMBINED WITH
DRAMATICALLY INCREASING VWS AND PERSISTENT NORTHEASTERLY SURGE
EVENT IMMEDIATELY TO THE NORTHWEST WILL RESULT IN STEADY WEAKENING, 
WITH FULL DISSIPATION EXPECTED AROUND OR SOON AFTER TAU 72.

MODEL DISCUSSION: THE NUMERICAL MODEL INTENSITY GUIDANCE SUITE 
DEMONSTRATES A FAIR DEGREE OF AGREEMENT THROUGHOUT THE FORECAST 
PERIOD, WITH ALL AVAILABLE GUIDANCE INICATING INITIAL INTENSIFICATION 
TO 35-40 KTS, FOLLOWED BY STEADY WEAKENING AFTERWARDS. THE INTENSITY 
SPREAD DURING THE LATTER STAGE IS APPROXIMATELY 20 KTS, RESULTING IN 
SOME UNCERTAINTY ASSOCIATED WITH THE TIMELINE OF THE DISSIPATION. AS A 
RESULT, INTENSITY FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE. IN 
REGARD TO THE TRACK, THE INITIAL 24-HOUR CROSS-TRACK SPREAD IS 38 NM 
INDICATING GOOD AGREEMENT. HOWEVER SHORTLY AFTER, MODEL GUIDANCE 
ENVELOPE OPENS UP SIGNIFICANTLY, REACHING 300 NM AT TAU 72, RESULTING 
IN LOW LONG-TERM TRACK CONFIDENCE. THE FASTEST AND TIGHTEST TURN IS 
PROJECTED BY NAVGEM, WHILE ECMWF MODELS ARE THE SLOWEST AND WIDEST IN 
REGARD TO THE TURN ANGLE. JTWC OFFICIAL TRACK FORECAST IS LAID IN 
RELATIVELY CLOSE PROXIMITY TO THE MULTI-MODEL CONSENSUS, SLIGHTLY ON 
THE OUTSIDE OF THE PROJECTED TURN.

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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