WDPN31 PGTW 172100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (NOKAEN) WARNING NR 
013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.3N 125.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 233 NM EAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 01W (NOKAEN) WITH A BROAD, POORLY DEFINED AND SHALLOW
LOW-LEVEL CIRCULATION CENTER (LLCC). REMAINING DEEP CONVECTION IS
NOW CONTAINED ONLY WITHIN THE NORTHERN SEMICIRCLE, WHILE THE
VERTICAL WIND SHEAR REMAINS LOW (10-15 KTS). STRONG UPPER-LEVEL 
OUTFLOW PATTERN PERSISTS, CONTRIBUTING TO THE MAINTENANCE OF SURFACE
INTENSITIES NEAR 45 KTS. HOWEVER, DRY MID-LEVEL AIR ENTERING THE
CORE OF THE VORTEX HAS PUT CENTRAL DEEP CONVECTION ON HOLD,
PARTICULARLY THROUGHOUT THE SOUTHERN SEMICIRCLE. THE INITIAL
POSITION IS ASSIGNED WITH MEDIUM CONFIDENCE, BASED ON THE ANIMATED EIR
IMAGERY AND A RECENT 171503Z OCEANSAT-3 OSCAT PASS DEPICTING AN AREA 
OF CALM WINDS CORRESPONDING TO THE MID-LEVEL TURNING SEEN IN THE
SATELLITE LOOP. THE INITIAL INTENSITY IS ALSO ASSESSED WITH MEDIUM
CONFIDENCE, SUPPORTED BY THE SUBJECTIVE AGENCY DVORAK ESTIMATES AND
CIMSS OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: A 171503Z OCEANSAT-3 OSCAT

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 47 KTS AT 171721Z
   CIMSS ADT: 47 KTS AT 171900Z
   CIMSS AIDT: 41 KTS AT 1711900Z
   CIMSS D-MINT: 42 KTS AT 171721Z
   CIMSS D-PRINT: 41 KTS AT 171830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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: TS 01W IS FORECAST TO TRANSIT ALONG THE
NORTHWESTERN PERIPHERY OF THE STR POSITIONED TO ITS EAST OVER THE
NEXT 48 HOURS. SUBSEQUENT TO TAU 24, THIS EASTERN STR IS PROJECTED
TO WEAKEN AND MIGRATE EASTWARD, CONCURRENT WITH THE EASTWARD
BUILDING OF A SEPARATE STR CENTERED OVER VIETNAM. FOLLOWING THIS
TRANSITION BETWEEN COMPETING STEERING RIDGES, TS 01W IS EXPECTED TO
BE STEERED SOUTH BETWEEN TAU 72 AND TAU 120 ALONG THE EASTERN
PERIPHERY OF THE WESTERN STR. REGARDING INTENSITY, A SLIGHT
DECREASE IN SURFACE INTENSITY TO 40 KTS IS FORECAST OVER THE NEXT
12 HOURS DUE TO THE CONTINUOUS WRAPPING OF DRY AIR INTO THE 
SOUTHEASTERN FLANK AND CORE OF THE SYSTEM. AROUND TAU 12, A BRIEF
REDUCTION IN VWS WILL ALLOW THE SYSTEM TO MAINTAIN ITS INTENSITY,
HOWEVER AFTER TAU 24, THE SHEAR WILL BEGIN TO INCREASE AGAIN. MORE
DRY AIR IS EXPECTED TO ENTRAIN THE CORE OF THE VORTEX RESULTING IN
WEAKENING AND EVENTUAL DISSIPATION, WHICH IS EXPECTED TO BEGIN AROUND
TAU 120. IF THE SYSTEM REMAINS SHALLOW, A MUCH FASTER WEAKENING IS
POSSIBLE, PARTICULARLY IF MULTIPLIED BY INTENSE NORTHERLY LOW-LEVEL
FLOW OVER THE SOUTHERN PHILIPPINE SEA.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE EXHIBITS FAIR
AGREEMENT THROUGH THE INITIAL 48 HOURS OF THE FORECAST PERIOD AS
THE SYSTEM NAVIGATES THE STR AXIS TO THE EAST. AS TS 01W BECOMES
INCREASINGLY INFLUENCED BY THE STR CENTERED OVER VIETNAM, NUMERICAL
MODEL TRACK GUIDANCE DIVERGES SIGNIFICANTLY. THROUGH THE INITIAL 48
HOURS, THE JTWC TRACK FORECAST REMAINS CLOSELY ALIGNED WITH THE
MULTI-MODEL CONSENSUS, LENDING MEDIUM CONFIDENCE TO THE SHORT-TERM
FORECAST. BEYOND THAT, CONFIDENCE IN THE JTWC FORECAST TRACK
DECREASES TO LOW, AS THE DOMINANT STEERING MECHANISM IS NOT CLEAR AND 
COULD BE INFLUENCED BY A REGIONAL NORTHERLY LOW-LEVEL FLOW. WITH 
RESPECT TO INTENSITY, ALL MEMBERS OF THE JTWC INTENSITY CONSENSUS SHOW 
SLOW AND STEADY WEAKENING, WITH A BRIEF PERIOD OF SUSTAINED INTENSITY 
DUE TO LOWER VWS. STATISTICAL-DYNAMICAL MODELS PREDICT A MUCH QUICKER 
DISSIPATION, AROUND TAU 72, WHILE OTHER GUIDANCE MAINTAINS GALES FORCE 
WINDS THROUGH AT LEAST TAU 120. 

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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