Advisories

WDPN31 PGTW 262100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 034//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.6N 125.3E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 183 NM NORTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A STEADILY 
BUT SLOWLY WEAKENING TYPHOON 17W, WHICH HAS MAINTAINED A 30NM WIDE, 
RAGGED EYE FEATURE OVER THE PAST SIX HOURS. THE PREVIOUSLY OBSERVED 
CLOUD-TOP WARMING HAS CEASED WITH THE APPROACH OF DIURNAL MAXIMUM AND 
SMALL POCKETS OF DEEP CONVECTION ARE REFORMING ALONG THE EASTERN 
FLANK OF THE EYE. A 261726Z NOAA-20 ATMS 89GHZ MICROWAVE IMAGE 
REVEALED A LARGE MICROWAVE EYE FEATURE, TILTED WESTWARD WITH 
REFERENCE TO THE LOWER-LEVEL EYE DUE TO THE PERSISTENT MODERATE 
EASTERLY SHEAR, AND MODERATE CONVECTIVE ACTIVITY ACROSS THE 
SOUTHEASTERN FLANK. THE INITIAL POSITION IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE 30NM WIDE EYE IN THE EIR AND THE MICROWAVE 
IMAGE DISCUSSED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM 
CONFIDENCE, BASED ON AN AVERAGE OF THE OBJECTIVE AND SUBJECTIVE 
INTENSITY ESTIMATES NOTED BELOW. ENVIRONMENTAL CONDITIONS ARE 
MARGINAL, WITH THE WARM SSTS AND MODERATE RADIAL OUTFLOW ALOFT BEING 
OFFSET BY THE MODERATE TO HIGH EASTERLY SHEAR AND STEADILY DECREASING 
OHC.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SYSTEM IS POSITIONED TO THE SOUTH OF A
WEAKNESS IN THE SUBTROPICAL RIDGE (STR). 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   CIMSS SATCON: 84 KTS AT 261728Z
   CIMSS ADT: 65 KTS AT 261730Z
   CIMSS AIDT: 71 KTS AT 261730Z
   CIMSS D-MINT: 86 KTS AT 261729Z
   CIMSS D-PRINT: 75 KTS AT 261800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: DRY MID-LEVEL AIR TO THE NORTH. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TYPHOON (TY) 17W IS CURRENTLY POSITIONED SOUTH
OF A WEAKNESS IN THE STR TO THE NORTH, WHICH HAS RESULTED IN THE 
SYSTEM SLOWLY DRIFTING NORTHWESTWARD OVER THE PAST 12 HOURS. OVER THE 
LAST SIX HOURS, THE SYSTEM HAS REACHED ITS SLOWEST FORWARD SPEED, BUT 
IMPORTANTLY, HAS BEGUN TO TURN WESTWARD AS THE STEERING PATTERN 
BEGINS TO SHIFT. TY 17W WILL CONTINUE TO TRACK GENERALLY WESTWARD FOR 
THE NEXT 12 HOURS AT A SLIGHTER FASTER SPEED THAN ITS CURRENTLY 
TRACKING. THE SYSTEM THEN TURNS MORE SOUTHWESTWARD AS A LARGE STR 
CENTERED OVER NORTH-CENTRAL CHINA BECOMES THE DOMINANT STEERING 
INFLUENCE. TY 17W IS FORECAST TO MAKE LANDFALL ALONG THE CHINESE 
COAST IN SOUTHERN ZHEJIANG PROVINCE BETWEEN TAU 24 AND TAU 36, BEFORE 
CONTINUING INLAND ALONG A WEST-SOUTHWESTWARD TRACK THROUGH TAU 60. 
REGARDING INTENSITY, THE SYSTEM IS EXPECTED TO SLOWLY WEAKEN AS IT 
APPROACHES THE CHINESE COAST DUE TO THE PERSISTENT MODERATE TO HIGH 
EASTERLY SHEAR AND DRY AIR ENTRAINMENT. ONCE THE SYSTEM MOVES ASHORE, 
IT WILL RAPIDLY DECAY DUE TO LAND INTERACTION AND FRICTIONAL EFFECTS, 
ULTIMATELY DISSIPATING OVER SOUTHEASTERN CHINA WITHIN THE NEXT 60 
HOURS.  

MODEL DISCUSSION: TRACK GUIDANCE IS IN STRONG AGREEMENT, WITH MINIMAL 
CROSS- OR ALONG-TRACK SPREAD THROUGH THE END OF THE FORECAST PERIOD. 
THE ONE NOTABLE EXCEPTION BEING THE EC-AIFS, WHICH TRACKS THE SYSTEM 
ON A MUCH MORE SOUTHWARD TRAJECTORY, ENDING THE SYSTEM JUST NORTH OF 
HONG KONG BY TAU 60. THE JTWC FORECAST IS PLACED NEAR THE MULTI-MODEL 
CONSENSUS MEAN THROUGH THE FORECAST PERIOD, WITH HIGH CONFIDENCE. 
INTENSITY GUIDANCE IS ALSO IN STRONG AGREEMENT, WITH ALL CONSENSUS 
MEMBERS INDICATING A SLOW WEAKENING OVER THE NEXT 24 HOURS, FOLLOWED 
BY A RAPID DECAY OVER LAND AND DISSIPATION WITH 60 HOURS. 

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