Advisories

WDPN31 PGTW 081500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15E (NOLO) WARNING NR 
072//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.6N 152.7E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 815 NM EAST-SOUTHEAST OF TOKYO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 15E (NOLO) WITH DEEP CONVECTION OFFSET TO THE WEST OF THE
LOW-LEVEL CIRCULATION CENTER (LLCC). A 081053Z METOP-B ASCAT
BULLSEYE PASS REVEALED AN ELONGATED AND SOMEWHAT ASYMMETRIC WIND
FIELD WITH THE BULK OF THE STRONGEST WINDS LOCATED WITHIN THE
NORTHERN SEMICIRCLE. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON EXTRAPOLATION FROM THE BROAD WIND MINIMUM IN
THE ASCAT PASS. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE ASCAT DATA ALONG WITH THE AGENCY
DVORAK FIXES AND CIMSS INTENSITY ESTIMATES LISTED BELOW.
ENVIRONMENTAL ANALYSIS INDICATES THAT 15E IS PLACED WITHIN A
MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD
OUTFLOW ALOFT, LOW TO MODERATE (15-20 KTS) VERTICAL WIND SHEAR, DRY
AIR ENTRAINMENT, AND WARM (27-28 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: 081053Z METOP-B ASCAT SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: A DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED 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: 49 KTS AT 081210Z
   CIMSS AIDT: 47 KTS AT 081210Z
   CIMSS D-PRINT: 42 KTS AT 081210Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT ALONG THE WESTERN PERIPHERY

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 IS FORECAST TO CONTINUE TRACKING 
WEST-NORTHWESTWARD, ALONG THE SOUTHWESTERN PERIPHERY OF THE
STR THROUGH TAU 24. 15E WILL THEN APPROACH THE STEERING RIDGE AXIS
NEAR TAU 24 AND BEGIN A NORTHWARD TURN. AROUND TAU 60, THE SYSTEM
WILL ACCELERATE NORTHEASTWARD AS IT TRACKS ALONG THE NORTHWESTERN
EXTENT OF THE STR AND STARTS TO INTERACT WITH THE STRONG UPPER-LEVEL
FLOW. EXTRATROPICAL TRANSITION IS FORECAST TO COMMENCE AT TAU 72
WITH COMPLETION NO LATER THAN TAU 96, ONCE 15E BECOMES EMBEDDED
UNDERNEATH THE JET. IN TERMS OF INTENSITY, 15E IS FORECAST TO
MARGINALLY INTENSIFY THROUGH TAU 24 DUE TO IMPROVING POLEWARD
OUTFLOW AND BRIEFLY DECREASING VERTICAL WIND SHEAR. AFTER TAU 36,
SOUTHWESTERLY SHEAR WILL QUICKLY INCREASE AND SEA SURFACE
TEMPERATURES WILL DROP, CAUSING 15E TO WEAKEN AS IT TRANSITIONS
INTO AN EXTRATROPICAL CYCLONE. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN MODERATE AGREEMENT
THROUGH TAU 72 WITH THE NOTABLE EXCEPTION OF THE GEFS ENSEMBLE
MEAN, WHICH IS MUCH SLOWER ROUNDING THE RIDGE THAN THE REMAINDER OF
GUIDANCE. AFTER TAU 72, ALONG-TRACK SPREAD INCREASES DRASTICALLY,
WITH THE VARIOUS AI-BASED MODELS FASTER THAN THE PHYSICS-BASED
MODELS. THE JTWC TRACK FORECAST IS PLACED NEAR THE MODIFIED
CONSENSUS (DISCOUNTING GEFS) WITH MEDIUM CONFIDENCE THROUGH TAU 72
AND THEN CLOSER TO THE AI-BASED MODELS THROUGH TAU 96 WITH LOW
CONFIDENCE. INTENSITY GUIDANCE AGREES ON A SLIGHT BUMP IN INTENSITY
THROUGH TAU 24 FOLLOWED BY WEAKENING. AS A RESULT, THE JTWC
INTENSITY FORECAST IS SET CLOSE TO THE MULTI-MODEL CONSENSUS
THROUGHOUT THE FORECAST PERIOD WITH HIGH CONFIDENCE THROUGH TAU 72
AND MEDIUM CONFIDENCE THEREAFTER.


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