Advisories

WDPN31 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15E (NOLO) WARNING NR 
076//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.4N 147.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 552 NM SOUTHEAST OF TOKYO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 15E (NOLO) WITH A SHALLOW BAND OF CONVECTION WRAPPING AROUND
THE WESTERN AND SOUTHERN PORTIONS OF A MOSTLY EXPOSED, YET
WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). A FIELD OF DRY
AIR TO THE WEST CONTINUES TO IMPACT THE VORTEX, LIMITING CONVECTIVE
ACTIVITY. A 091055Z METOP-C ASCAT PASS REVEALED A SYMMETRIC CORE OF
40-45 KNOT WINDS AND GALE-FORCE WINDS WEIGHTED MORE ON THE NORTHERN
SEMICIRCLE. THE INITIAL POSITION, INTENSITY, AND WIND RADII ARE ALL
PLACED WITH HIGH CONFIDENCE BASED ON THE BULLSEYE ASCAT PASS. THE
DVORAK-BASED ESTIMATES CONTINUE TO UNDERESTIMATE THE CURRENT
INTENSITY OF 15E DUE TO THE LACK OF CENTRAL CONVECTION.
ENVIRONMENTAL ANALYSIS INDICATES A MARGINAL ENVIRONMENT
CHARACTERIZED BY STRONG POLEWARD OUTFLOW ALOFT, LOW TO MODERATE
(15-20 KTS) VERTICAL WIND SHEAR, AND BORDERLINE (26-27 C) SEA
SURFACE TEMPERATURES GREATLY OFFSET BY THE SIGNIFICANT DRY AIR
ENTRAINMENT.

INITIAL WIND RADII BASIS: 091055Z METOP-C ASCAT SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   CIMSS ADT: 32 KTS AT 091220Z
   CIMSS AIDT: 37 KTS AT 091220Z
   CIMSS D-MINT: 37 KTS AT 091121Z
   CIMSS D-PRINT: 50 KTS AT 091220Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT THROUGHOUT THE
WESTERN PERIPHERY


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

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
NORTHWESTWARD, ALONG THE SOUTHWESTERN PERIPHERY OF THE STR, FOR
ONLY ANOTHER 12 HOURS. NEAR TAU 12, 15E WILL BEGIN TO TURN
NORTHWARD AS IT ROUNDS THE WESTERN EXTENT OF THE STR. TRACK SPEEDS
WILL START TO INCREASE NEAR TAU 36 AS THE SYSTEM TURNS
NORTHEASTWARD AND TRAVERSES THE POLEWARD SIDE OF THE RIDGE.
EXTRATROPICAL TRANSITION IS FORECAST TO BEGIN AT TAU 48 AND
COMPLETE NO LATER THAN TAU 60, ONCE THE SYSTEM BECOMES EMBEDDED
UNDERNEATH THE STRONG UPPER-LEVEL JET. IN TERMS OF INTENSITY, 15E
IS FORECAST TO MAINTAIN ITS CURRENT INTENSITY OF 50 KTS THROUGH TAU
12, PRIMARILY DUE TO THE STRONG POLEWARD OUTFLOW CHANNEL. AFTER TAU 
12, 15E IS FORECAST TO WEAKEN THROUGH TAU 60 AS WESTERLY SHEAR QUICKLY
INCREASES AND SEA SURFACE TEMPERATURES DROP. SOME MODELS,
PARTICULARLY THE GFS, ACTUALLY SHOW 15E DISSIPATING BEFORE FULLY
ROUNDING THE RIDGE AND COMPLETING EXTRATROPICAL TRANSITION. THIS IS
CURRENTLY ANALYZED TO BE LESS LIKELY DUE TO THE CURRENT SOLID
STRUCTURE OF THE LLCC.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN MODERATE AGREEMENT
WITH A SLIGHT BIFURCATION PRESENT IN THE GUIDANCE. AS PREVIOUSLY
MENTIONED, GFS AND UKMET BOTH SHOW 15E FAILING TO COMPLETE THE
RECURVE AND STALLING NEAR THE 34N LATITUDE AT TAU 48. THE REMAINDER
OF GUIDANCE SHOWS THE SYSTEM COMPLETING THE RECURVE AND TRACKING
OFF TO THE NORTHEAST. THE JTWC TRACK FORECAST IS PLACED WITHIN THE
MEAN OF THE LATTER GROUPING WITH MEDIUM CONFIDENCE. INTENSITY
GUIDANCE, DESPITE DIFFERENCES IN THE TRACK, IS IN GOOD AGREEMENT ON
STEADY WEAKENING FOLLOWING TAU 12. AS A RESULT, THE JTWC INTENSITY
FORECAST IS SET CLOSE TO THE CONSENSUS THROUGHOUT THE FORECAST
PERIOD WITH HIGH CONFIDENCE.

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