Advisories

WDPN31 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15E (NOLO) WARNING NR 
075//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.8N 148.7E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 609 NM SOUTHEAST OF TOKYO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 15E (NOLO) WITH A MOSTLY EXPOSED, YET WELL-DEFINED, LOW-LEVEL
CIRCULATION CENTER (LLCC) AND A FRAGMENTED BAND OF CONVECTION ALONG
THE WESTERN SEMICIRCLE. A FIELD OF DRY AIR, INDICATED BY STABLE
STRATOCUMULUS CLOUDS, CAN BE SEEN SPILLING INTO THE CORE FROM THE
NORTH AND WEST, LIKELY PREVENTING CONVECTION FROM BUILDING OVER THE
CENTER. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED
ON THE EXPOSED CENTER IN ANIMATED MSI. THE INITIAL INTENSITY OF 50
KTS IS ASSESSED WITH MEDIUM CONFIDENCE AND IS SET HIGHER THAN THE
INTENSITY ESTIMATES LISTED BELOW WOULD SUGGEST. THIS IS IN RESPONSE
TO THE ESTIMATES LIKELY UNDERESTIMATING THE CURRENT INTENSITY DUE
TO THE LACK OF CENTRAL CONVECTION ASSOCIATED WITH THE SYSTEM.
ENVIRONMENTAL ANALYSIS INDICATES A MARGINAL ENVIRONMENT
CHARACTERIZED BY STRONG POLEWARD OUTFLOW ALOFT, LOW (10-15 KTS)
VERTICAL WIND SHEAR, AND BORDERLINE (26-27 C) SEA SURFACE
TEMPERATURES GREATLY OFFSET BY THE SIGNIFICANT DRY AIR ENTRAINMENT.

INITIAL WIND RADII BASIS: PERSISTENCE WITH SLIGHT ADJUSTMENTS MADE
BASED ON THE OBJECTIVE BEST TRACK

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: 31 KTS AT 090540Z
   CIMSS AIDT: 41 KTS AT 090540Z
   CIMSS D-PRINT: 45 KTS AT 090540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 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: MEDIUM
   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
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 AROUND 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 LOW SHEAR AND A STRONG POLEWARD OUTFLOW CHANNEL.
AFTER TAU 12, 15E IS FORECAST TO STEADILY 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 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
A 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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