Advisories

WDPN31 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15E (NOLO) WARNING NR 
073//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.8N 151.1E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 745 NM SOUTHEAST OF TOKYO, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 27 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TS 15E HAS STRUGGLED TO MAINTAIN INTENSITY OVER THE PAST SIX HOURS.
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A NEAR
DISSIPATION OF ALL DEEP CONVECTION, BUT A STILL TIGHTLY WRAPPED
MID-LEVEL CIRCULATION. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE NEAR THE MID-POINT OF RECENT FIXES FROM PGTW, RJTD, AND
RCTP AND IS CONSISTENT WITH EXTRAPOLATION FROM THE PREVIOUS BEST
TRACK POSITION. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE HIGH END OF AVAILABLE SUBJECTIVE
DVORAK AND AUTOMATED INTENSITY ESTIMATES TO ACCOUNT FOR A POTENTIAL
LOW BIAS IN THOSE TECHNIQUES DUE TO THE RECENT, AND LIKELY TEMPORARY,
DISSIPATION OF DEEP CONVECTION OVER THE CIRCULATION.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK AND PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS ADT: 37 KTS AT 081750Z
   CIMSS AIDT: 41 KTS AT 081810Z
   CIMSS D-MINT: 39 KTS AT 081542Z
   CIMSS D-PRINT: 49 KTS AT 081810Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE 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 15E WILL TURN POLEWARD AND EASTWARD AROUND
THE WESTERN PERIPHERY OF THE CURRENT STEERING RIDGE DURING THE 72
HOUR FORECAST PERIOD. THE SYSTEM WILL INTERACT WITH A SHALLOW
SHORTWAVE TROUGH APPROACHING FROM THE WEST AND COMPLETE
EXTRATROPICAL TRANSITION AFTER TAU 48. DESPITE NOTED TRENDS IN
SATELLITE IMAGERY, TS 15E IS EXPECTED TO INTENSIFY SLIGHTLY OVER
THE NEXT 24 HOURS AS IT PASSES OVER SUFFICIENTLY WARM WATER,
VERTICAL WIND SHEAR REMAINS LOW TO MODERATE, AND IS IMPACTED BY A 
FAVORABLE OUTFLOW PATTERN SUPPORTING RENEWED CONVECTIVE ACTIVITY. 
HOWEVER, AFTER TAU 24 THE SYSTEM WILL ENCOUNTER INCREASING VERTICAL 
WIND SHEAR AND ENTRAINMENT OF DRIER AIR FROM THE WEST AS IT ROUNDS 
THE STEERING RIDGE AXIS, DRIVING A STEADY WEAKENING TREND. FAVORABLE 
BAROCLINIC SUPPORT SHOULD ALLOW THE SYSTEM TO MAINTAIN TROPICAL STORM 
LEVEL INTENSITY AS IT COMPLETES EXTRATROPICAL TRANSITION.

MODEL DISCUSSION: NUMERICAL MODEL TRACK AND INTENSITY FORECAST
GUIDANCE ARE BOTH IN GOOD AGREEMENT REGARDING THE OVERALL SCENARIO,
INCLUDING A TIGHT TURN AROUND THE STEERING RIDGE AND SLIGHT
NEAR-TERM INTENSIFICATION FOLLOWED BY GRADUAL WEAKENING AFTER TAU
24. PHYSICAL-BASED MODELS BROADLY DEPICT A WIDER AND SLOWER TURN
THAN THE AI-BASED MODELS, RESULTING IN SIGNIFICANT CROSS-TRACK AND
ALONG-TRACK SPREAD BY TAU 72. THERE IS NO CLEAR FACTOR FAVORING
EITHER SOLUTION SET, AND OVERALL SPREAD AMONG ALL OF THE AVAILABLE
GUIDANCE IS SPREAD EVENLY BETWEEN THE WESTERN AND EASTERN EDGES OF
THE ENVELOPE. THE CURRENT FORECAST LIES ALONG A PLAUSIBLE TRACK IN
THE MID-POINT OF ALL GUIDANCE, JUST SLIGHTLY TO THE WEST OF THE
PREVIOUS JTWC TRACK FORECAST AS THE SYSTEM MAKES THE TURN. THE
INTENSITY FORECAST IS CONSISTENT WITH CONSENSUS GUIDANCE AND THE
PREVIOUS FORECAST, WITH UNCERTAINTY PRIMARILY CONFINED TO THE NEXT
24 HOURS GIVEN FAVORABLE ENVIRONMENTAL CONDITIONS BUT A POOR
SATELLITE PRESENTATION.

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