Advisories

WDPN31 PGTW 210300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (SAUDEL) WARNING NR 
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.7N 149.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 188 NM EAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
CONTINUOUS DEEP CONVECTION AROUND THE CENTRAL CORE OF TROPICAL
STORM (TS) 17W AND DEEP CONVECTIVE BANDS AROUND ALL BUT THE
NORTHWEST QUADRANT.  A 202236Z GMI 89 GHZ MICROWAVE IMAGE REVEALS
THAT THE LOW LEVEL STRUCTURE CONTINUES TO SYMMETRIZE AND EXPAND,
WITH EXTENSIVE LOW CLOUD BANDS THAT ARE BEGINNING TO EXHIBIT
FLARING CONVECTION. A 202334Z METOP-B ASCAT IMAGE SHOWS SOME
ASYMMETRY OF THE WIND FIELD IN THE NORTHWEST QUADRANT AND A SWATH
OF 45 KT WINDS IN THE SOUTHEAST QUADRANT. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION FROM THE GMI
MICROWAVE IMAGE AND AGENCY DVORAK FIX POSITIONS. THE INITIAL
INTENSITY OF 45 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
ASCAT WIND SPEEDS AND T3.0 AGENCY FIXES. THE ENVIRONMENT IS
CHARACTERIZED AS HIGHLY FAVORABLE FOR INTENSIFICATION WITH LOW
VERTICAL WIND SHEAR (VWS), VERY WARM SEA SURFACE TEMPERATURES, HIGH
OCEAN HEAT CONTENT (OHC), ABUNDANT DEEP-LAYER MOISTURE, AND ROBUST
OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A SUBTROPICAL
RIDGE (STR) CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 42 KTS AT 202100Z
   CIMSS ADT: 41 KTS AT 210010Z
   CIMSS AIDT: 42 KTS AT 210010Z
   CIMSS D-MINT: 39 KTS AT 202234Z
   CIMSS D-PRINT: 43 KTS AT 210010Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 17W (SAUDEL) HAS MAINTAINED A NORTHWESTWARD
TRACK OVER THE PAST 12 HOURS UNDER THE STEERING INFLUENCE OF THE
STR SITUATED TO THE NORTHEAST. THE NORTHWESTWARD TRAJECTORY IS
FORECAST TO CONTINUE THROUGH TAU 12 IN THIS STEERING ENVIRONMENT.
BETWEEN TAU 24-36, AN EXTENSION OF THE STEERING RIDGE IS EXPECTED
TO CONTINUE BUILDING WESTWARD AND INDUCE A WEST-NORTHWESTWARD TRACK
THROUGH THE REMAINDER OF THE FORECAST PERIOD. A SECOND STR CENTERED
OVER KYUSHU IS ALSO EXPECTED TO BUILD SOUTHEASTWARD DURING THE
LATER PERIOD OF THE FORECAST AND AID IN MAINTAINING THE
WEST-NORTHWESTWARD TRACK OF 17W. REGARDING INTENSITY, TS 17W
REMAINS IN A HIGHLY FAVORABLE ENVIRONMENT AND CONTINUES TO
CONSOLIDATE. A LENGTHY PERIOD OF RAPID INTENSIFICATION (RI) THROUGH
TAU 36 IS EXPECTED IN THIS ENVIRONMENT. ONCE THE SYSTEM EXITS THE
REGION OF HIGH OHC THE INTENSIFICATION RATE WILL SLOW UNTIL IT
REACHES A PEAK OF 120 KTS AROUND TAU 60. AFTER TAU 60, LOWER OHC,
INCREASING VWS, AND POTENTIAL EYEWALL REPLACEMENT CYCLES ARE
EXPECTED TO CAP THE INTENSIFICATION AND RESULT IN A STEADY GRADUAL
WEAKENING PHASE.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH
TAU 72, WITH A CROSS-TRACK SPREAD OF 70 NM AT THAT TIME. AFTER TAU
72, THE GFS TRACKER TURNS POLEWARD AND BECOMES AN OUTLIER, WHILE
THE REMAINDER OF PRIMARY GUIDANCE AND EXPERIMENTAL AI TRACKERS
MAINTAIN A WEST-NORTHWESTWARD TRACK TOWARD THE RYUKYU ISLANDS,
ALTHOUGH STILL WITH A 180 NM CROSS-TRACK SPREAD AT TAU 120. THE
JTWC TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS
THROUGHOUT THE FORECAST PERIOD WITH HIGH CONFIDENCE THROUGH TAU 72
AND MEDIUM CONFIDENCE THEREAFTER. THE MODEL INTENSITY GUIDANCE IS
IN GOOD AGREEMENT ABOUT THE NEAR-TERM RI SCENARIO, WITH SEVERAL RI
AIDS CONTINUING TO TRIGGER THIS CYCLE. ALL INTENSITY GUIDANCE
AGREES ON THE INTENSITY PROFILE THROUGHOUT THE FORECAST PERIOD AND
THE JTWC INTENSITY FORECAST IS PLACED ON THE UPPER END OF THE
ENVELOPE IN ANTICIPATION OF A NEAR-TERM RI.

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