Advisories

WDPN34 PGTW 100300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (FIFTEEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.6N 160.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 522 NM NORTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION 15W WITH A SMALL SYMMETRICAL CENTRAL DENSE OVERCAST
(CDO) FEATURE OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC). A
092248Z METOP-C ASCAT PASS REVEALED THAT THE WIND FIELD IS HIGHLY
ASYMMETRIC WITH A MARKED WEAKNESS IN THE WESTERN SEMICIRCLE. WINDS
ON THE EASTERN SIDE WERE MEASURED TO BE AROUND 25-30 KTS, LENDING
HIGH CONFIDENCE TO THE INITIAL INTENSITY ASSESSMENT. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE MSI AND
EXTRAPOLATION FROM THE ASCAT PASS. ENVIRONMENTAL ANALYSIS INDICATES
THAT TD 15W IS IN A MARGINAL ENVIRONMENT CHARACTERIZED BY MODERATE
POLEWARD OUTFLOW ALOFT, LOW TO MODERATE (15-20 KTS) WESTERLY
VERTICAL WIND SHEAR, DRY AIR ENTRAINMENT, AND WARM (29-30 C) SEA
SURFACE TEMPERATURES.

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

CURRENT STEERING MECHANISM: LARGE-SCALE DEEP-LAYER CYCLONIC FLOW
CENTERED TO THE NORTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T1.5 - 25 KTS
   PHFO: T2.0 - 30 KTS
   CIMSS D-PRINT: 36 KTS AT 100000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE WEST

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TD 15W IS FORECAST TO TRACK NORTHWARD WITHIN
THE LARGE-SCALE CYCLONIC FLOW THROUGH THE REST OF ITS SHORT LIFESPAN. 
AN INCOMING UPPER-LEVEL TROUGH IS EXPECTED TO PROPAGATE EASTWARD AND 
CRASH INTO 15W, INDUCING OVER 30 KTS OF WESTERLY SHEAR ON THE SYSTEM 
WITHIN THE NEXT 12 HOURS. THE HIGH SHEAR COMBINED WITH AN ASYMMETRIC 
WIND FIELD IS EXPECTED TO QUICKLY WEAKEN 15W. COMPLETE DISSIPATION AND 
UNRAVELING OF THE VORTEX IS FORECAST TO OCCUR AROUND TAU 24.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN RELATIVELY
POOR AGREEMENT CONSIDERING HOW SHORT THE FORECAST PERIOD IS.
CROSS-TRACK SPREAD AT TAU 24 IS OVER 100 NM, WHICH IS PRIMARILY DUE
TO THE ECMWF DETERMINISTIC TRACKER SHOWING AN IMMINENT NORTHWESTWARD 
TURN. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL 
CONSENSUS WITH MEDIUM CONFIDENCE. RELIABLE INTENSITY GUIDANCE AGREES 
ON WEAKENING THROUGH TAU 24 AND THE JTWC INTENSITY FORECAST FOLLOWS 
SUIT. 

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