Tropical Storm NAMTHEUN Advisory Sun Oct 17

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (NAMTHEUN) WARNING NR 026//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 30.8N 165.3E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 694 NM NORTH OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
CONSOLIDATING SYSTEM WITH A COMPACT CORE AND INTENSE DEEP CONVECTIVE
BURSTS NEAR THE CENTER. THE IMPROVED CONVECTIVE STRUCTURE IS CLEARLY
EVIDENT IN THE 160221Z AMSR2 89GHZ AND 160431Z SSMIS 91GHZ MICROWAVE
IMAGES, WHICH SHOW DEEP CONVECTIVE BANDING WRAPPING TIGHTLY INTO A
MICROWAVE EYE FEATURE. THUS, THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE. ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE WITH LOW
VERTICAL WIND SHEAR (VWS), MODERATE OUTFLOW AND WARM SST NEAR 26-
27C. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE CIMSS SATCON ESTIMATE AND A 160219Z AMSR2
WINDSPEED IMAGE SHOWING 65-66 KNOT PEAK WINDS. THIS IS HEDGED ABOVE
THE PGTW, KNES DVORAK ESTIMATES AND BELOW THE UW-CIMSS ADT CURRENT
INTENSITY ESTIMATES OF 4.4 (74-75 KNOTS). IN GENERAL, THE SYSTEM
APPEARS TO HAVE PEAKED AROUND 160300Z NEAR 65-70 KNOTS WITH A SLIGHT
DEGRADATION IN CONVECTIVE STRUCTURE SINCE THAT TIME.
INITIAL WIND RADII BASIS: SCATTEROMETER DATA
CURRENT STEERING MECHANISM: SOUTH-SOUTHWEST TO NORTH-NORTHEAST
ORIENTED SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 64 KTS AT 160232Z
   CIMSS ADT: 74 KTS AT 160540Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT OVER THE WESTERN SEMICIRCLE.
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TY 23W IS EXPECTED TO ACCELERATE NORTH-
NORTHEASTWARD TO NORTHWARD THROUGH TAU 36 ALONG THE WESTERN
PERIPHERY OF THE STR. SIGNIFICANT WEAKENING WILL OCCUR AS SEA
SURFACE TEMPERATURES RAPIDLY COOL FROM 26C TO 21C BY TAU 36.
ADDITIONALLY, VWS WILL INCREASE TO MODERATE LEVELS AS THE SYSTEM
BEGINS EXTRA-TROPICAL TRANSITION (ETT) AND INTERACTS WITH THE
BAROCLINIC ZONE NEAR TAU 24. AFTER TAU 36, TY 23W WILL RECURVE
NORTHEASTWARD AS IT ROUNDS THE NORTHWEST PERIPHERY OF THE STR.
FURTHER WEAKENING WILL OCCUR AS SEA SURFACE TEMPERATURES COOL
FURTHER TO 16C, VWS INCREASES TO 30-35 KNOTS AND ETT COMPLETES. TY
23W SHOULD GAIN FRONTAL CHARACTERISTICS BY TAU 48 AS IT BEGINS TO
TRACK NEAR JET-STRENGTH UPPER LEVEL WINDS.
MODEL DISCUSSION: WITH THE EXCEPTION OF AFUM, NUMERICAL MODEL
GUIDANCE IS IN TIGHT AGREEMENT THROUGH THE FORECAST PERIOD WITH A
50 NM SPREAD IN SOLUTIONS AT TAU 48. INTENSITY GUIDANCE IS ALSO IN
GOOD AGREEMENT AND SUPPORTS THE STEADY WEAKENING TREND. THEREFORE,
CONFIDENCE IN THE JTWC TRACK AND INTENSITY FORECAST IS HIGH.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: HIGH//
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