Advisories

WDPN31 PGTW 192100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (SAUDEL) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.5N 152.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 188 NM NORTH-NORTHEAST OF CHUUK
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 17W WITH A POORLY DEFINED, MOSTLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH THE BULK OF CONVECTION REMAINING IN
THE SOUTHERN SEMICIRCLE. SOME FLARING CONVECTION HAS STARTED TO
DEVELOP IN THE SOUTHEASTERN QUADRANT BUT HAS SO FAR FAILED TO WRAP
INTO THE NORTHEASTERN QUADRANT. A 191521Z AMSR-2 89 GHZ MICROWAVE
IMAGE REVEALED THE ELONGATION OF THE LLCC ALONG A
SOUTHWEST-NORTHEAST AXIS. A HEALTHY EQUATORWARD OUTFLOW CHANNEL IS
APPARENT IN ANIMATED WATER VAPOR IMAGERY, SUPPORTING UPPER-LEVEL
OUTFLOW. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON THE LLCC IN ANIMATED EIR AND EXTRAPOLATION FROM THE LLCC
IN THE AMSR-2 MICROWAVE IMAGE. THE INITIAL INTENSITY OF 35 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF THE AGENCY
DVORAK FIXES AND CIMSS OBJECTIVE INTENSITY ESTIMATES. THE
ENVIRONMENT IS CHARACTERIZED AS FAVORABLE, WITH WARM SEA SURFACE
TEMPERATURES, GOOD OUTFLOW ALOFT, AND LOW VERTICAL WIND SHEAR
(VWS).

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMBINED INFLUENCE OF THE SOUTHWESTERN
EXTENT OF A SUBTROPICAL RIDGE (STR) POSITIONED FAR TO THE NORTHEAST
AND A NEAR EQUATORIAL RIDGE (NER) TO THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS D-MINT: 29 KTS AT 191529Z
   CIMSS D-PRINT: 26 KTS AT 191810Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM (TS) 17W (SAUDEL) HAS
ACCELERATED NORTHWESTWARD OVER THE PAST 6 HOURS PRIMARILY UNDER THE
INFLUENCE OF THE NER TO THE SOUTHEAST. THE TRACK IS FORECAST TO
CONTINUE NORTHWESTWARD THROUGH TAU 72 AS THE STR TO THE NORTHEAST
BUILDS AND TAKES CONTROL OF THE STEERING ENVIRONMENT. THE
AFOREMENTIONED STR IS EXPECTED TO MIGRATE WESTWARD AS IT BUILDS AND
STEER 17W ONTO A WEST-NORTHWESTWARD TRACK AFTER TAU 72. A SLOWER
RATE OF INTENSIFICATION TO 45 KTS IS EXPECTED OVER THE NEXT 12
HOURS DUE TO THE DISORGANIZED NATURE OF THE SYSTEM. ONCE THE SYSTEM
BECOMES MORE ORGANIZED AND SYMMETRIC, A PERIOD OF RAPID
INTENSIFICATION (RI) IS FORECAST FROM TAU 12-36 IN A HIGHLY
FAVORABLE ENVIRONMENT OF WARM SEA SURFACE TEMPERATURES, HIGH OCEAN
HEAT CONTENT, AND LOW VWS. TS17W IS EXPECTED TO REACH A PEAK
INTENSITY OF 125 KTS AROUND TAU 72 UNDER THESE CONDITIONS, THEN
GRADUALLY WEAKEN THROUGH THE REMAINDER OF THE FORECAST PERIOD.
WEAKENING AFTER TAU 72 MAY BE ATTRIBUTABLE TO AN EYEWALL
REPLACEMENT CYCLE, WHICH IS SUGGESTED BY THE HAFS-A MODEL FIELDS
AROUND THAT TIME.

MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS IN GOOD AGREEMENT
ABOUT THE NORTHWESTWARD TRAJECTORY THROUGH TAU 72, WITH A
CROSS-TRACK SPREAD OF 80 NM AT THAT TIME. THERE IS SOME ALONG-TRACK
SPREAD AT TAU 72, WITH NAVGEM AND JGSM AS FAST OUTLIERS BY ABOUT
125 NM WHILE THE REMAINDER OF GUIDANCE AGREES ON A SLOWER TRACK
SPEED. THE CROSS-TRACK AT TAU 120 IS 125 NM, AN IMPROVEMENT FROM THE
PREVIOUS MODEL RUNS. THE JTWC TRACK FORECAST IS PLACED NEAR THE
MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE THROUGH TAU 72 AND
MEDIUM CONFIDENCE THEREAFTER. MODEL INTENSITY GUIDANCE AGREES ON
INTENSIFICATION, INCLUDING THE PERIOD OF RI BETWEEN TAU 12-36, WITH
THE EXCEPTION OF SHIPS GUIDANCE, WHICH DEPICTS A MUCH SLOWER RATE
OF INTENSIFICATION. INTENSITY GUIDANCE SPREADS 20KT ENVELOPE BY TAU
120, LENDING LOW CONFIDENCE TO THE LATER PORTION OF THE INTENSITY
FORECAST.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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