Advisories

WDPN32 PGTW 130300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (PEILOU) WARNING 
NR 025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.1N 166.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 786 NM NORTHEAST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS THE FULLY
EXPOSED, ELONGATED LOW LEVEL CIRCULATION CENTER OF TROPICAL DEPRESSION 
(TD) 13W. FLARING CONVECTION REMAINS CONFINED TO THE EASTERN 
SEMICIRCLE AND IS QUICKLY SHEARED FROM THE NORTHWEST, WHILE DRY AIR 
ENTRAINMENT IS EVIDENT IN MSI BY THE FIELD OF STRATOCUMULUS CLOUDS ON 
THE WESTERN FLANK. FURTHER ANALYSIS REVEALS A WHOLLY UNFAVORABLE 
ENVIRONMENT CHARACTERIZED BY MODERATE TO HIGH (20-25 KTS) VERTICAL 
WIND SHEAR, MARGINAL (26-27 C) SEA SURFACE TEMPERATURES, AND WEAK 
POLEWARD OUTFLOW ALOFT. A 122318Z METOP-C ASCAT FURTHER CONFIRMS THE 
ELONGATED LLCC AND ASYMMETRICAL WIND FIELD, WITH ALL 25-30 KT WINDS 
BEING CONFINED TO THE SOUTHEAST QUADRANT. THE INITIAL POSITION IS 
PLACED WITH HIGH CONFIDENCE BASED ON MSI AND ASCAT DATA. THE INITIAL 
INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON ASCAT DATA AS IT 
IS MORE REPRESENTATIVE THAN THE SPREAD OF AGENCY DVORAK FIXES AND 
CIMSS OBJECTIVE ESTIMATES LISTED BELOW WHICH STRUGGLE WITH SYSTEMS 
LACKING CONVECTION.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: EASTERN EXTENSION OF A NEAR-EQUATORIAL
RIDGE (NER) CENTERED TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.0 - 25 KTS
   CIMSS SATCON: 36 KTS AT 122210Z
   CIMSS ADT: 26 KTS AT 122330Z
   CIMSS AIDT: 27 KTS AT 122330Z
   CIMSS D-MINT: 34 KTS AT 122252Z
   CIMSS D-PRINT: 28 KTS AT 122330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST PHILOSOPHY HAS CHANGED
TO EXTRATROPICAL TRANSITION RATHER THAN DISSIPATION OVER WATER.

FORECAST DISCUSSION: TD 13W IS FORECAST TO CONTINUE TRACKING 
NORTHEASTWARD WITH INCREASING TRACK SPEED FOR THE REMAINDER OF THE
FORECAST PERIOD UNDER THE STEERING INFLUENCE OF THE EASTERN EXTENSION 
OF A NEAR-EQUATORIAL RIDGE CENTERED TO THE SOUTH. A SIGNIFICANT CHANGE 
TO THE FORECAST HAS BEEN MADE, AS TD 13W IS EXPECTED TO BEGIN 
EXTRATROPICAL TRANSITION (ETT) BY TAU 24 AS IT CROSSES THE 26 C 
ISOTHERM, APPROACHES THE UPPER LEVEL JET, INCREASED VWS, AND FURTHER 
DRY AIR ENTRAINMENT WILL CAUSE THE SYSTEM TO CONTINUE TO ELONGATE AND 
BECOME EMBEDDED WITHIN THE LARGER TROUGH CENTERED TO THE NORTHEAST, 
ULTIMATELY COMPLETING ETT BY TAU 36. REGARDING INTENSITY, TD 13W IS 
EXPECTED TO INTENSIFY DURING THIS TRANSITION AND BE FULLY 
EXTRATROPICAL WITH GALE STRENGTH WINDS.

MODEL DISCUSSION: TRACK MODEL GUIDANCE REMAINS IN GOOD AGREEMENT ON
THE NORTHEASTWARD TRACK OF TD 13W FOR THE REMAINDER OF THE FORECAST
PERIOD. THE OFFICIAL JTWC FORECAST TRACK IS PLACED WITH HIGH 
CONFIDENCE, CLOSELY IN LINE WITH THE MULTI-MODEL CONSENSUS. INTENSITY 
MODEL GUIDANCE IS IN GOOD AGREEMENT ON THE INTENSIFICATION OUT TO TAU 
36 AS TD 13W COMPLETES ETT. THE OFFICIAL JTWC INTENSITY FORECAST IS 
ASSESSED WITH HIGH CONFIDENCE, SLIGHTLY BELOW THE MULTI-MODEL 
CONSENSUS AND ENDING EARLIER AS THE BULK OF THE GUIDANCE DOES NOT 
REPRESENT THE FORECAST ETT ACCURATELY.

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