Advisories

WDPN33 PGTW 240900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 19W (ATSANI) WARNING 
NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.1N 138.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 552 NM SOUTH-SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY EXPOSED 
LOW-LEVEL CIRCULATION CENTER (LLCC) ASSOCIATED WITH TROPICAL 
DEPRESSION (TD) 19W (ATSANI). THE LLCC PROPAGATED RAPIDLY 
NORTHEASTWARD OVER THE LAST 06 HOURS, STEERED BY THE COMBINED EFFECTS 
OF LOW- TO MID-LEVEL SOUTHWESTERLIES ASSOCIATED WITH A NEAR-EQUATORIAL 
RIDGE (NER) TO THE EAST-SOUTHEAST, IN TANDEM WITH THE SOUTHEASTWARD 
FLANK OF A SUBTROPICAL RIDGE CENTERED TO THE NORTHEAST - WHICH, IN 
TURN, SERVES AS THE PRIMARY STEERING MECHANISM FOR TYPHOON 17W. 
ADDITIONALLY, THE TWO SYSTEMS ARE WITHIN THE BINARY INTERACTION 
DISTANCE THRESHOLD. THE INITIAL POSITION IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE CLEAR LLCC OBSERVED IN THE VISIBLE SATELLITE 
IMAGERY LOOP. ENVIRONMENTAL ANALYSIS INDICATES MARGINALLY UNFAVORABLE 
DEVELOPMENT CONDITIONS. ALTHOUGH SEA SURFACE TEMPERATURES (SST) REMAIN 
CONDUCIVE AT 29-30C AND UPPER-LEVEL DYNAMICS BENEFIT FROM AN 
EQUATORWARD OUTFLOW PATTERN, SEVERE NORTHEASTERLY VERTICAL WIND SHEAR 
(VWS) OF 30+ KTS LIMITS ANY INTENSIFICATION. FURTHERMORE, WHILE 
TROPOSPHERIC MOISTURE IS RELATIVELY HIGH ALONG THE WESTERN PERIPHERY, 
SIGNIFICANT MID-LEVEL DRY-AIR INTRUSION IS INCREASING, DUE TO THE 
SURROUNDING DRY AIR MASS ENVELOPING AND CONSTRAINING THE CORE. THE 
INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE, AS NO 
NEW WIND SPEED DATA IS AVAILABLE, WHILE OBJECTIVE AIDS AND SUBJECTIVE 
AGENCY FIXES PRESENT A SLIGHTLY INCREASED VARIABILITY.

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

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SOUTHWESTERLIES DRIVEN 
BY SOUTHEASTWARD EXTENSION OF A SUBTROPICAL RIDGE CENTERED TO THE 
NORTHEAST, WHICH IS THE PRIMARY STEERING MECHANISM FOR TYPHOON 17W.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 38 KTS AT 240540Z
   CIMSS ADT: 35 KTS AT 240610Z
   CIMSS AIDT: 33 KTS AT 240610Z
   CIMSS D-MINT: 32 KTS AT 240442Z
   CIMSS D-PRINT: 27 KTS AT 240610Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE
   VWS: 30+ KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: PERSISTENT DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE 
FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TD 19W IS FORECAST TO CONTINUE TRACKING 
NORTHEASTWARD OVER THE NEXT 06-12 HOURS BEFORE GRADUALLY VEERING 
NORTHWARD AND FOLLOWING IN THE WAKE OF TY 17W ALONG THE SOUTHWESTERN 
PERIPHERY OF A STR ANCHORED TO THE NORTHEAST. THE SYSTEM IS BEGINNING 
ITS TERMINAL WEAKENING PHASE, DRIVEN PRIMARILY BY HOSTILE VWS AND 
INCREASING DRY-AIR ENTRAINMENT. AS SUCH, IT IS EXPECTED TO RETAIN 30 
KTS INTENSITY FOR A SHORT PERIOD OF TIME. IT WILL LIKELY STRUGGLE TO 
RETAIN SYMMETRY AND WILL BEGIN TO OPEN UP, PARTICULARLY OVER THE 
WESTERN SEMICIRCLE. THESE DESTRUCTIVE DYNAMIC AND THERMODYNAMIC 
IMPEDIMENTS WILL PERSIST, LEADING TO THE STEADY DECAY OF TD ATSANI. 
INTENSITY IS EXPECTED TO DEPRESS TO 25 KTS BY TAU 24, CULMINATING IN 
COMPLETE DISSIPATION OVER OPEN WATER WITHIN THE NEXT 36 HOURS.

MODEL DISCUSSION: NUMERICAL WEATHER PREDICTION SPREAD EXHIBITS HIGH 
TRACK CONSISTENCY, DEPICTING A TIGHT 90-NM CROSS-TRACK DISPERSION 
ENVELOPE THROUGH TAU 36. ALONG-TRACK UNCERTAINTY IS MODERATE,   
CONSTRAINED TO APPROXIMATELY 200 NM SPREAD BETWEEN THE MAJORITY OF THE 
TRACKERS AND THE SLOWEST ECMWF AND UKMET GUIDANCE. THE OFFICIAL JTWC 
TRACK IS POSITIONED ON THE EASTERN SIDE OF THE MULTI-MODEL CONSENSUS 
WITH HIGH CONFIDENCE, OFFSETTING THE MUCH SLOWER AND TIGHTER-TURNING 
UKMET TRACKER. IN TERMS OF INTENSITY, ALL AVAILABLE GUIDANCE MEMBERS 
PROJECT TERMINAL WEAKENING, WITH DISSIPATION ESTIMATED BETWEEN TAUS 24 
AND 36. WHILE PREVIOUS RUNS FROM COAMPS-TC RECENTLY ACTED AS OUTLIERS 
PROGNOSTICATING PEAK SPEEDS OF 50-55 KTS, CURRENT CONSENSUS MEMBERS 
HAVE FULLY REALIGNED WITH A STEADY WEAKENING SCENARIO, SECURING HIGH 
CONFIDENCE IN THE DISSIPATION OUTLOOK.

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