Advisories

WDPN31 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15E (NOLO) WARNING NR 
077//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.0N 147.2E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 495 NM SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS THE
LOW-LEVEL CIRCULATION CENTER (LLCC) OF TROPICAL STORM (TS) 15E
(NOLO) BECOMING DECOUPLED FROM AND OBSCURED BY THE UPPER-LEVEL
CONVECTION. THE LOWER- TO MID-LEVEL ROTATION REMAINS VIGOROUS
BENEATH THE COLLAPSING UPPER-LEVELS. 15E RECENTLY CROSSED THE 26C
ISOTHERM INTO COOLER WATER, ELIMINATING OCEANIC SUPPORT TO THE
LOWER LEVELS. ENVIRONMENTAL ANALYSIS REVEALS AN UNFAVORABLE
ENVIRONMENT, CHARACTERIZED BY MODERATE TO HIGH (20-25 KTS) VERTICAL
WIND SHEAR (VWS), COOL (25-26 C) SEA SURFACE TEMPERATURES,
SIGNIFICANT DRY AIR ENTRAINMENT, OFFSET SOLELY BY THE ROBUST
POLEWARD OUTFLOW CHANNEL. THE INITIAL POSITION IS PLACED WITH LOW
CONFIDENCE BASED ON THE FULLY OBSCURED LLCC. THE INITIAL INTENSITY
OF 50 KTS IS ASSESSED WITH LOW CONFIDENCE BASED ON THE AUTOMATED
CIMSS INTENSITY ESTIMATES, SUPPLEMENTED BY THE AGENCY DVORAK FIXES.
THE AGENCY DVORAK FIXES ARE ASSESSED TO BE UNDERESTIMATING THE
ACTUAL INTENSITY DUE TO THE LACK OF ORGANIZED DEEP CONVECTION.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN EXTENT OF A SUBTROPICAL RIDGE
(STR) CENTERED TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   CIMSS ADT: 33 KTS AT 091910Z
   CIMSS AIDT: 47 KTS AT 091740Z
   CIMSS D-MINT: 34 KTS AT 091607Z
   CIMSS D-PRINT: 57 KTS AT 091840Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: LOW
   INITIAL WIND RADII: LOW

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
NORTH-NORTHWEST FOR THE NEST 12 HOURS WHILE IT REMAINS EQUATORWARD
OF THE STEERING RIDGE AXIS. AROUND TAU 12, 15E WILL CROSS THE RIDGE
AXIS AND RECURVE TO THE NORTHEAST. 15E WILL MAINTAIN A
NORTHEASTWARD TRAJECTORY THROUGH THE REMAINDER OF THE FORECAST
PERIOD, BEGINNING EXTRATROPICAL TRANSITION NO LATER THAN TAU 36 AND
COMPLETING TRANSITION BY TAU 48. REGARDING INTENSITY, 15E IS
EXPECTED TO STEADILY WEAKEN THROUGH THE FORECAST PERIOD, AS THE
ENVIRONMENT CONTINUES TO DETERIORATE AS THE SYSTEM TRACKS POLEWARD.
THE SYSTEM'S CURRENT INTENSITY IS SUSTAINED ONLY BY THE STRONG
POLEWARD OUTFLOW CHANNEL, WHICH IS EXPECTED TO DEGRADE BY TAU 24.
ALSO, BY TAU 24, VWS IS EXPECTED TO INCREASE TO 30 KTS AND FORCE
COPIOUS AMOUNTS OF DRY AIR INTO THE CORE. BY TAU 36, 15E WILL BEGIN
INTERACTING WITH THE UPPER-LEVEL WESTERLIES AND ENTER THE
BAROCLINIC ZONE, THUS BEGINNING ITS TRANSITION INTO AN
EXTRATROPICAL SYSTEM. 15E IS EXPECTED TO BE FULLY EXTRATROPICAL AT
TAU 48, BUT IT WILL LIKELY COMPLETE TRANSITION SOONER.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN DECENT
AGREEMENT THROUGH TAU 24, BUT DIVERGES THEREAFTER AS MODELS
DISAGREE ON THE SPEED AND TIMING OF THE RECURVE. THE ALONG-TRACK
SPREAD COMPOUNDS INTO A 300 NM SPREAD AT TAU 48 BETWEEN THE SLOWEST
(GEFS MEAN) AND THE FASTEST (GSM) MEMBERS. OF NOTE, THE GFS
DETERMINISTIC AND ENSEMBLE MEAN DEPICT 15E DISSIPATING BEFORE
RECURVING AND GOING EXTRATROPICAL, EXPLAINING THE SIGNIFICANT LAG
IN THOSE MODELS SPECIFICALLY. A SCENARIO WHERE NOLO DISSIPATES
PRIOR TO COMPLETING EXTRATROPICAL TRANSITION HAS BEEN DEEMED
UNLIKELY, THOUGH NOT IMPOSSIBLE GIVEN THE ANTICIPATED HOSTILE
ENVIRONMENT. AS A RESULT, THE JTWC TRACK FORECAST IS PLACED CLOSER
TO THE ECMWF AND GSM MODEL SOLUTIONS AND DEPICTS AN EXTRATROPICAL
TRANSITION. THE JTWC TRACK FORECAST IS PLACED WITH OVERALL MEDIUM
CONFIDENCE. RELIABLE INTENSITY AIDS ARE IN STRONG AGREEMENT,
LENDING HIGH CONFIDENCE TO THE JTWC INTENSITY FORECAST. 

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