Advisories

WDPN31 PGTW 090300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15E (NOLO) WARNING NR 
074//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.2N 149.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 680 NM SOUTHEAST OF TOKYO, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TS 15E HAS MAINTAINED INTENSITY OVER THE PAST SIX HOURS WILL
SUPPORT FROM FAVORABLE UPPER-LEVEL FLOW AND PASSAGE OVER WARM
WATER. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS
LIMITED, PATCHY DEEP CONVECTION OVER A WELL-DEFINED LOW-LEVEL
CIRCULATION AND STRATOCUMULUS CLOUD LINES TRACING A DRIER AIR MASS
TO THE WEST OF THE CIRCULATION, WHICH MAY ALREADY BE INFLUENCING
THE SYSTEM. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON TIGHTLY-GROUPED SATELLITE FIXES FROM PGTW, RJTD, AND RCTP
AND ON A CLEAR CENTER FEATURE EVIDENT UPSTREAM IN A 082018Z WSF-M 
PASS. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM 
CONFIDENCE CONSISTENT WITH THE HIGH END OF SUBJECTIVE DVORAK AND 
AUTOMATED INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK AND PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS ADT: 33 KTS AT 082350Z
   CIMSS D-MINT: 46 KTS AT 082339Z
   CIMSS D-PRINT: 41 KTS AT 090110Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: ENTRAINMENT OF DRIER AIR FROM THE WEST

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: FORECAST INTENSITIES HAVE DECREASED
SLIGHTLY FROM THE PREVIOUS WARNING. OTHERWISE, 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 IS EXPECTED TO INTERACT WITH A
SHALLOW SHORTWAVE TROUGH APPROACHING FROM THE WEST AND COMPLETE
EXTRATROPICAL TRANSITION AFTER TAU 48. FAVORABLE UPPER-LEVEL
SUPPORT AND PASSAGE OVER WARM WATER WILL ALLOW TS 15E TO MAINTAIN
INTENSITY AS A MID-RANGE TROPICAL STORM OVER THE NEXT 24 HOURS,
WITH THE POTENTIAL FOR A SMALL TERM BOOST BY TAU 24. THEREAFTER,
THE SYSTEM WILL ENCOUNTER INCREASING VERTICAL WIND SHEAR AND
ENTRAINMENT OF DRIER AIR FROM THE WEST WILL INCREASE SIGNIFICANTLY
AS IT ROUNDS THE STEERING RIDGE AXIS, DRIVING A STEADY WEAKENING
TREND. BAROCLINIC SUPPORT SHOULD BE SUFFICIENT TO ALLOW THE SYSTEM TO 
MAINTAIN TROPICAL DEPRESSION 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 WEAKENING AFTER TAU 24.
PHYSICS-BASED MODELS DEPICT A WIDER AND SLOWER TURN THAN THE
AI-BASED MODELS, RESULTING IN SIGNIFICANT CROSS-TRACK AND
ALONG-TRACK SPREAD BY TAU 72. THE CURRENT TRACK FORECAST HOLDS
STEADY WITH THE PREVIOUS JTWC FORECAST, SET JUST SLIGHTLY TO THE
WEST AND MORE CONSISTENT WITH THE AI-BASED MODELS. ADDITIONAL
ADJUSTMENTS MAY BE NECESSARY ON SUBSEQUENT FORECASTS UNTIL GUIDANCE
COMES INTO BETTER ALIGNMENT, AND CONFIDENCE CAN ONLY BE
CHARACTERIZED AS MEDIUM AT THIS POINT. THE INTENSITY FORECAST IS
CONSISTENT WITH CONSENSUS GUIDANCE, WHICH HAS DROPPED A BIT SINCE THE
PREVIOUS FORECAST CYCLE. GIVEN TRENDS IN SATELLITE PRESENTATION AND
MODEL GUIDANCE, DISSIPATION OF THE CIRCULATION PRIOR TO
EXTRATROPICAL TRANSITION IS NOW A POSSIBILITY, ALTHOUGH IT IS THE LESS
LIKELY SCENARIO.

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