Advisories

WDPN32 PGTW 101500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (PEILOU) 
WARNING NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.6N 152.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 170 NM SOUTH-SOUTHWEST OF MINAMI TORI
SHIMA
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION (TD) 13W (PEILOU) LOOKING DECEPTIVELY GOOD, WITH A
RADIALLY EXPANDING CENTRAL DENSE OVERCAST AND COOLING CLOUD TOPS.
HOWEVER, THE 101134Z ASCAT DATA REVEALS THAT SYSTEM HAS WEAKENED
CONSIDERABLY, AND APPEARS TO BE BECOMING INCREASINGLY WEAK AND
ELONGATED IN THE NORTHERN QUADRANT. THE STRONGEST WINDS CAPTURED BY
THE ASCAT WERE 30 KT WINDS CONFINED TO THE SOUTHERN QUADRANT,
COLLOCATED WITH THE STRONG MONSOONAL WESTERLIES. ENVIRONMENTAL
ANALYSIS REVEALS A MARGINAL ENVIRONMENT, CHARACTERIZED BY LOW TO
MODERATE (15-20 KTS) VERTICAL WIND SHEAR (VWS), WARM (28-29 C) SEA
SURFACE TEMPERATURES (SST), AND MODERATE POLEWARD OUTFLOW, OFFSET
BY DRY AIR ENTRAINMENT. THE INITIAL POSITION AND INITIAL INTENSITY
ARE PLACED WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED 101134Z
ASCAT DATA.

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

CURRENT STEERING MECHANISM: LOW-LEVEL WESTERLY MONSOONAL FLOW AND
EASTERN EXTENSION OF A NEAR EQUATORIAL RIDGE (NER) CENTERED TO THE
SOUTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 52 KTS AT 101030Z
   CIMSS ADT: 51 KTS AT 101230Z
   CIMSS AIDT: 39 KTS AT 101230Z
   CIMSS D-MINT: 51 KTS AT 101151Z
   CIMSS D-PRINT: 44 KTS AT 101230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: UPPER-LEVEL TROUGH POSITIONED TO THE NORTHWEST,
IN VERY CLOSE PROXIMITY TO THE SYSTEM

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: TD 13W WEAKENED UNEXPECTEDLY FROM 40
KTS AT 100600Z TO 30 KTS AT 101200Z. THEREFORE, THE FORECAST HAS
BEEN ADJUSTED TO REFLECT THE UPDATED INTENSITIES AND QUICKER
EXPECTED WEAKENING.

FORECAST DISCUSSION: TD 13W IS FORECAST TO CONTINUE TRACKING
EAST-NORTHEASTWARD FOR THE DURATION OF THE FORECAST PERIOD, WHILE
THE SHALLOW VORTEX REMAINS UNDER THE STEERING INFLUENCE OF THE
STRONG MONSOONAL WESTERLIES AND THE WEAK EASTWARD EXTENSION OF THE
NER CENTERED IN THE PHILIPPINE SEA. REGARDING INTENSITY, 13W IS
FORECAST TO GRADUALLY WEAKEN THROUGH TAU 48 AS ITS ENVIRONMENT
BECOMES INCREASINGLY UNFAVORABLE. THE UPPER-LEVEL TROUGH CURRENTLY
SUPPORTING MODERATE POLEWARD OUTFLOW IS EXPECTED TO WEAKEN AND PASS
OVER THE SYSTEM AROUND TAU 12, INDUCING STRONGER NORTHWESTERLY VWS
AND SIGNIFICANT DRY AIR ENTRAINMENT. THE COMBINATION OF THESE
FACTORS, PLUS THE LOSS OF THE UPPER-LEVEL SUPPORT PROVIDED BY THE
TROUGH, IS ANTICIPATED TO HASTEN PEILOU'S TERMINAL WEAKENING TREND.
13W IS EXPECTED TO OPEN INTO A SURFACE TROUGH AND FORFEIT TROPICAL
CHARACTERISTICS NO LATER THAN TAU 48.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG
AGREEMENT THROUGH TAU 60, SUPPORTING THE JTWC TRACK FORECAST WITH
HIGH CONFIDENCE. THE ONLY SIGNIFICANT OUTLIER IS NAVGEM, WHICH WAS
DISCOUNTED WHILE CREATING THE TRACK FORECAST. LIKEWISE, RELIABLE
INTENSITY GUIDANCE IS IN STRONG AGREEMENT IN A GRADUAL WEAKENING
TREND THROUGHOUT THE DURATION OF THE FORECAST PERIOD, SUPPORTING
THE JTWC INTENSITY FORECAST WITH HIGH CONFIDENCE.


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