Advisories

WDPN31 PGTW 080900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15E (NOLO) WARNING NR 
071//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.4N 154.1E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 882 NM EAST-SOUTHEAST OF TOKYO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 15E (NOLO) WITH WARMING CLOUD TOPS AND A MORE DISORGANIZED
CONVECTIVE STRUCTURE. DRY AIR CAN BE SEEN SPILLING IN FROM THE
NORTH ALONG THE WESTERN PERIPHERY OF 15E, AND IS LIKELY THE PRIMARY
CAUSE OF THE DEGRADING APPEARANCE. A 080513Z SSMIS 91 GHZ MICROWAVE
IMAGE REVEALED A BAND OF CONVECTION DISPLACED TO THE WEST OF THE
ASSESSED CENTER. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE ANIMATED MSI AND SSMIS MICROWAVE IMAGE. 
THE INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY DVORAK AND CIMSS INTENSITY ESTIMATES LISTED
BELOW. ENVIRONMENTAL ANALYSIS INDICATES THAT 15E REMAINS PLACED
WITHIN A MARGINAL ENVIRONMENT CHARACTERIZED BY MODERATE OUTFLOW
ALOFT, MODERATE (15-20 KTS) SOUTHEASTERLY VERTICAL WIND SHEAR, 
DRY AIR ENTRAINMENT, AND WARM (27-28 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: THE 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: T3.5 - 55 KTS
   CIMSS ADT: 49 KTS AT 080610Z
   CIMSS AIDT: 54 KTS AT 080610Z
   CIMSS D-MINT: 51 KTS AT 080513Z
   CIMSS D-PRINT: 48 KTS AT 080610Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT ALONG THE WESTERN PERIPHERY

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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
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 BY TAU 96, ONCE 15E BECOMES EMBEDDED UNDERNEATH THE JET. 
IN TERMS OF INTENSITY, 15E IS FORECAST TO MARGINALLY INTENSIFY FROM
TAU 12 TO TAU 36 DUE TO IMPROVING POLEWARD OUTFLOW AND BRIEFLY
DECREASING VERTICAL WIND SHEAR. AFTER TAU 36, SOUTHWESTERLY SHEAR
WILL QUICKLY INCREASE TO OVER 40 KTS 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 36 FOLLOWED BY WEAKENING WITH NO SIGNIFICANT OUTLIERS.
THE JTWC INTENSITY FORECAST IS SET CLOSE TO THE MULTI-MODEL
CONSENSUS THROUGHOUT THE FORECAST PERIOD WITH MEDIUM CONFIDENCE.

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