WDPN31 PGTW 130300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SEVENTEEN) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 7.1N 138.3E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 144 NM SOUTH OF YAP
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LOW-LEVEL
CIRCULATION CENTER (LLCC) POSITIONED EAST-SOUTHEAST OF A REGION OF
RAGGED FLARING CONVECTION. THE SYSTEM CONTINUES TO STRUGGLE TO
CONSOLIDATE AS THE DEEPEST CONVECTION IS DISPLACED TO THE WESTERN
AND SOUTHERN QUADRANTS OF THE LLCC DUE TO THE IMPACT OF EASTERLY
OUTFLOW ALOFT. ADDITIONALLY, MID-LEVEL DRY AIR UNDER THE
SUBTROPICAL RIDGE (STR) TO THE NORTH CONTINUES TO HINDER CONVECTION
AROUND THE NORTHERN AND EASTERN SEMICIRCLES. A 122140Z SSMIS 91 GHZ
MICROWAVE IMAGE DEPICTS FORMATIVE BANDING OVER THE WESTERN AND
NORTHERN SEMICIRCLE OF THE LLCC. THE INITIAL POSITION IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE PARTIALLY EXPOSED CIRCULATION
DEPICTED IN THE MSI IMAGERY ALONG WITH THE SSMIS MICROWAVE IMAGERY.
THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
THE AVERAGE OF THE AGENCY DVORAK INTENSITY ESTIMATES RANGING
BETWEEN T1.5 AND T2.0. OVERALL, THE ENVIRONMENT IS ASSESSED AS
MARGINAL, CHARACTERIZED BY MODERATE EASTERLY DIFFLUENT OUTFLOW
ALOFT, MODERATE TO HIGH EASTERLY VERTICAL WIND SHEAR (VWS), WARM
(30-31C) SEA SURFACE TEMPERATURES (SSTS), AND DRY AIR IN THE
MID-LEVELS.

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

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 32 KTS AT 122330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE WESTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: OVER THE NEXT 24-36 HOURS, TD 17W (SEVENTEEN)
IS FORECAST TO TRACK SLOWLY GENERALLY WESTWARD DUE TO AN OVERALL
WEAK STEERING GRADIENT ASSOCIATED WITH THE DEEP-LAYER RIDGE TO THE
NORTH-NORTHEAST. AFTER TAU 48, 17W WILL ACCELERATE TO THE
WEST-NORTHWEST AS THE STEERING RIDGE TO THE NORTH-NORTHEAST IS
EXPECTED TO RESTRENGTHEN AND EXTEND WEST. THE SYSTEM WILL CONTINUE
TO TRACK WEST-NORTHWEST THROUGH TAU 72, AFTER WHICH ANOTHER BREAK
IN THE STEERING RIDGE IS EXPECTED TO OCCUR, ALLOWING 17W TRACK
GENERALLY NORTHWESTWARD THROUGH TAU 120. THE INTENSITY FORECAST
REMAINS OVERALL CONSISTENT WITH THE PREVIOUS FORECAST. 17W WILL
STRUGGLE TO DEVELOP THROUGH TAU 48 DUE TO THE OVERALL DISORGANIZED
LOW-LEVEL STRUCTURE AND THE PRESENCE OF DRY MID-LEVEL AIR AND
MODERATE TO HIGH EASTERLY SHEAR. AFTER TAU 48, THE SYSTEM IS
EXPECTED TO EXPERIENCE A GRADUAL INTENSIFICATION TREND AS 17W IS
EXPECTED TO TRANSIT INTO A MORE FAVORABLE ENVIRONMENT OF SLIGHTLY
LOWER SHEAR AND ENHANCED MID-LEVEL MOISTURE. THEREFORE, 17W IS
FORECAST TO REACH A PEAK INTENSITY OF 45 KNOTS BY TAU 96.

MODEL DISCUSSION: NUMERICAL MODELS CONTINUE TO SUGGEST THE SYSTEM
WILL DRIFT SLOWLY WESTWARD THROUGH TAU 48. FOLLOWED BY A MORE
NORTHWESTWARD TRACK THROUGH TAU 120. OVERALL, NUMERICAL MODEL
GUIDANCE IS IN FAIR AGREEMENT WITH A 107NM SPREAD IN TRACK GUIDANCE
BY TAU 72. CROSS-TRACK SPREAD INCREASES TO 200NM BY TAU 120. THE
INTENSITY GUIDANCE CONTINUES TO BE IN GOOD AGREEMENT OVERALL, WITH
GLOBAL AND MESOSCALE MODELS ALL SHOWING GRADUAL INTENSIFICATION
THROUGHOUT THE FORECAST PERIOD. THE JTWC INTENSITY FORECAST FOLLOWS
CLOSE TO THE MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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