Tropical Storm NANMADOL Advisory Sa, 17.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 16W (NANMADOL) WARNING NR
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 26.0N 133.1E
   INITIAL INTENSITY: 130 KTS
   GEOGRAPHIC REFERENCE: 287 NM EAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 52 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A VERY LARGE
TYPHOON, IN TERMS OF ITS OUTER RAIN BANDS AND WIND FIELD, WITH A
COMPACT INNER CORE OF SYMMETRICAL DEEP CONVECTION SURROUNDING A
20NM WIDE EYE, WITH TEMPERATURE NEAR 20C. CONFIDENCE IN THE
INITIAL POSITION IS HIGH BASED ON THE EYE FEATURE AND AGREEMENT OF
ALL AGENCY FIX POSITIONS. A LACK OF RECENT MICROWAVE IMAGERY
PRECLUDES DETAILED ASSESSMENT OF THE INNER STRUCTURE OF THE SYSTEM,
BUT THE LAST SSMIS PASS AT 162014Z SHOWED A VERY SMALL RING OF DEEP
CONVECTION INSIDE OF 20NM FROM THE CENTER AND HINTED AT THE
DEVELOPMENT OF A SECONDARY EYEWALL ON THE EASTERN PERIPHERY OF THE
SYSTEM. IT IS HIGHLY PROBABLE THAT THE SYSTEM IS CURRENTLY IN THE
EARLY PHASES OF AN EYEWALL REPLACEMENT CYCLE (ERC) BUT WE WILL JUST
HAVE TO WAIT FOR MICROWAVE DATA TO CONFIRM IT. THE INITIAL
INTENSITY HAS BEEN LOWERED TO 130 KNOTS BASED PRIMARILY ON A
162107Z RADARSAT-2 SYNTHETIC APERTURE RADAR PASS WHICH SHOWED A
MAXIMUM WIND OF 125 KNOTS IN THE NORTHWEST EYEWALL. WHILE AGENCY
AND OBJECTIVE FIX CURRENT INTENSITY (CI) VALUES REMAIN BETWEEN T6.5
AND T7.0, ALL SHOW T6.5 FINAL-T VALUES, MORE IN LINE WITH THE ADT,
PROVIDING ADDITIONAL CONFIDENCE IN A SLIGHTLY LOWER INTENSITY. THE
WIND RADII HAVE ALSO BEEN UPDATED WITH HIGH CONFIDENCE BASED ON THE
SAR DATA. OVERALL THE ENVIRONMENT REMAINS FAVORABLE WITH WARM SSTS,
LOW VWS AND MODERATE RADIAL OUTFLOW ALOFT. THE UPPER-LEVEL PATTERN IS
COMPLEX, WITH ANTICYCLONES TO THE NORTHEAST AND WEST AND A SMALL
POINT SOURCE DIRECTLY OVER STY 16W PROVIDING THE RADIAL OUTFLOW
SOURCE.
INITIAL WIND RADII BASIS: SAR DATA
CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE EAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T7.0 - 140 KTS
   RJTD: T7.0 - 140 KTS
   KNES: T6.5 - 127 KTS
   CIMSS ADT: 132 KTS AT 162340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: IN THE NEAR-TERM (36 HOURS) THERE IS LITTLE
DOUBT THAT STY 16W WILL TRACK STEADILY NORTHWESTWARD ALONG THE
SOUTHWEST SIDE OF THE STEERING RIDGE TO THE EAST, PASSING JUST
SOUTHWEST OF YAKU SHIMA ISLAND AFTER TAU 24 AND ENTERING THE EAST
CHINA SEA TO THE WEST OF KYUSHU. DUE TO AN EXPECTED ERC, THE SYSTEM
IS FORECAST TO WEAKEN SLIGHTLY OVER THE NEXT 12 HOURS. THOUGH IT
MAY IN FACT COMPLETE AN ERC, BY THAT TIME IT WILL BE MOVING OVER A
PATCH OF RELATIVELY LOW OHC WATERS AND WON'T BE ABLE TO RECOVER ITS
FORMER INTENSITY, THOUGH IT IS STILL EXPECTED TO BE A 120 KNOT
TYPHOON AT TAU 24. A STRONG COLD FRONT AND ACCOMPANYING 500MB
SHORTWAVE TROUGH, CURRENTLY MOVING ACROSS NORTHERN CHINA, WILL OVER
THE NEXT 24 TO 48 HOURS STEADILY MOVE EASTWARD AND BEGIN TO ERODE
THE STEERING RIDGE. BY TAU 36 THIS MID-LATITUDE SYSTEM WILL BEGIN TO
HAVE A DIRECT IMPACT ON BOTH THE STEERING AND INTENSITY OF STY 16W.
THE SYSTEM IS FORECAST TO TURN SHARPLY TO THE NORTHEAST AFTER TAU
36, TURNING INBOUND TO A LANDFALL IN THE VICINITY OF NAGASAKI BY
TAU 48, THEN RAPIDLY ACCELERATING TO THE NORTHEAST ALONG THE
FRONTAL BOUNDARY. WESTERLY SHEAR WILL BEGIN IMPACTING THE SYSTEM BY
TAU 36, AND COMBINED WITH COOLING SSTS AND WEAK CONVERGENCE ALOFT,
WILL MARK THE ONSET OF MORE RAPID WEAKENING, DOWN TO 105 KNOTS BY
TAU 36 WITH ADDITIONAL WEAKENING ANTICIPATED BY TAU 48 DUE TO THE
ADDITION OF SIGNIFICANT LAND INTERACTION AS THE SYSTEM TRACKS CLOSE
TO THE COAST OF KYUSHU. AFTER TAU 48 THE SYSTEM LAYS ON THE GAS
PEDAL AND ACCELERATES RAPIDLY NORTHEASTWARD ALONG THE FRONTAL
BOUNDARY PUSHING IN FROM THE WEST WHILE BEING TORN APART BY A
COMBINATION OF ELEVATED SHEAR IN THE UPPER LEVELS AND TERRAIN
INFLUENCES IN THE LOWER LEVELS. THE END RESULT WILL BE RAPID
WEAKENING IN CONJUNCTION WITH EXTRA-TROPICAL TRANSITION. BY TAU 96
THE DRASTICALLY WEAKENED REMNANTS WILL EXIT INTO THE PACIFIC
NORTHEAST OF TOKYO AND BECOME FULLY EXTRATROPICAL NO LATER THAN TAU
120.
MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH
TAU 36 WITH ALL CONSENSUS MEMBERS CONFINED TO A 75NM ENVELOPE WITH
NAVGEM SLOW AND TO THE WEST AND JGSM FAST AND TO THE RIGHT OF THE
ENVELOPE. BY TAU 48, SIGNIFICANT DIFFERENCES BEGIN TO EMERGE AS THE
MODELS ARE HANDLING THE TIMING AND STRENGTH OF THE TURN TO THE
NORTHEAST DIFFERENTLY. BY TAU 48, THE ENVELOPE SPREAD INCREASES TO
220NM WITH NAVGEM HANGING BACK SOUTHWEST OF SASEBO WHILE JGSM AND
THE UKMET MODELS START TO PULL AWAY TO THE NORTHEAST. THESE TRENDS
ARE EXACERBATED THROUGH TAU 72, AS THE SPREAD INCREASES TO 640NM
BETWEEN NAVGEM AND THE UKMET MODELS. AT THIS POINT THERE IS
SIGNIFICANT UNCERTAINTY IN THE FORECAST SCENARIO. THE NAVGEM, ECMWF
AND TO LESSER EXTENT THE HWRF, SHOW THE SYSTEM UNDERGOING EXTREMELY
RAPID DISSIPATION AND THE REMNANT CIRCULATION PUSHING SOUTH OF
SHIKOKU BY TAU 120, PUSHED SOUTH BY THE STRONG NORTHERLY FLOW ALONG
THIS SECTION OF THE COLD FRONT. THE UKMET MODELS AND GALWEM
MEANWHILE RACE THE SYSTEM NORTHEAST AT OVER 35 KNOTS ALONG THE MORE
PARALLEL FLOW SECTION OF THE COLD FRONT, WITH THE TAU 120 POSITION
EXTENDING TO EAST OF THE KURILS, RESULTING IN A SPREAD OF WELL OVER
1700NM THE END OF THE FORECAST PERIOD. THE GFS AND ECMWF
INTERMEDIATE MODEL TAKE A MORE MEASURED MEAN BETWEEN THE TWO
EXTREMES. THE JTWC FORECAST REMAINS CONSISTENT WITH THE PREVIOUS
FORECAST WITH A TRACK SHIFTED JUST SLIGHTLY FURTHER SOUTHWARD AFTER
TAU 48. CONFIDENCE IS HIGH THROUGH TAU 36 BUT LOW THEREAFTER. THE
JTWC FORECAST LIES ON THE HIGH EDGE OF THE INTENSITY GUIDANCE,
WHICH SHOWS STRONG AGREEMENT ON THE OVERALL WEAKENING TREND, WITH
MEDIUM CONFIDENCE.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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