Tropical Storm NANMADOL Advisory So, 18.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (NANMADOL) WARNING NR 022//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 29.7N 131.0E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 215 NM SOUTH-SOUTHEAST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT WHILE TY
16W REMAINS VERY LARGE IN OVERALL EXTENT, WITH OUTER RAIN BANDS
EXTENDING FROM OKINAWA TO NORTHERN KYUSHU, THE INNER CORE REGION OF
DEEP CONVECTION REMAINS FAIRLY SMALL, ABOUT 100NM IN DIAMETER. IN
THE VISIBLE IMAGERY, NO EYE IS DISCERNABLE, THOUGH THERE IS A SMALL
DIMPLE WHICH LINES UP WITH A RAGGED EYE-LIKE FEATURE IN THE
BD-ENHANCED INFRARED IMAGERY. THE JMA RADAR AT TUNE SHOWS MULTIPLE
RAINBANDS WRAPPING INTO THE WELL-DEFINED EYE ABOUT 35-40NM
SOUTHEAST OF YAKUSHIMA ISLAND, MOVING TOWARDS THE NORTH-NORTHWEST
AT 12 KNOTS. IN THE PREVIOUS DISCUSSION THERE WAS CONCERN WITH A
SHARP WOBBLE TO THE EAST, BUT OVER THE PAST SIX HOURS, TRACK MOTION
HAS SMOOTHED OUT AND THE TRACK MADE GOOD HAS STEADIED UP ON 345
DEGREES AND THE SYSTEM DOES NOT CURRENTLY SHOW MUCH OF A WOBBLE.
LANDFALL IS EXPECTED IN THE VICINITY OF YAKUSHIMA WITHIN THE NEXT
COUPLE OF HOURS AND THE OBSERVATION SITE THERE IS CURRENTLY
REPORTING WINDS UP TO 55 KNOTS AND PRESSURE FALLS OF ROUGHLY 6MB
PER HOUR AS THE SYSTEM APPROACHES. THE INITIAL INTENSITY IS LOWERED
TO 105 KNOTS, AS THE SYSTEM CONTINUES TO STRUGGLE TO RE-ESTABLISH A
STRONG POST-ERC INNER CORE IN THE FACE OF STRONG (50-70 KNOT)
MID-LEVEL WINDS PUNCHING IN FROM THE WEST, AS INDICATED IN THE
0000Z NAZE SOUNDING. THE BULK OF AGENCY CURRENT INTENSITY ESTIMATES
AND THE ADT CONGEALED AROUND T5.5 (102 KNOTS) THOUGH THE FINAL-T
VALUES ARE DROPPING PRECIPITOUSLY. MEANWHILE RADAR VELOCITY DATA
SHOWED ROUGHLY 110 KNOTS IN THE LOWER LEVELS, LENDING HIGH
CONFIDENCE TO THE INITIAL INTENSITY ASSESSMENT. THE ENVIRONMENT IS
CURRENTLY CHARACTERIZED AS MARGINAL DUE TO INCREASING WESTERLY
SHEAR IN THE MID-LEVELS AND REDUCED OUTFLOW ON THE WESTERN SIDE DUE
TO THE PRESENCE OF A SECONDARY UPPER-LEVEL ANTICYCLONE OVER THE
EAST CHINA SEA.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: NEARING THE AXIS OF THE SUBTROPICAL
RIDGE (STR) TO THE EAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T5.5 - 102 KTS
   RJTD: T5.0 - 90 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 116 KTS AT 172229Z
   CIMSS ADT: 102 KTS AT 172340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: STRONG MID-LEVEL WESTERLIES, IMPINGED OUTFLOW TO
THE WEST AND DECREASING SSTS.
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: LOW
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: THOUGH THERE COULD BE ANOTHER ROUND OF WOBBLES
AS THE SYSTEM TURNS MORE NORTHWARD OVER THE NEXT 12 HOURS, NO MAJOR
CHANGES IN THE TRACK ARE ANTICIPATED. WHILE THERE IS A SLIGHT
CHANCE OF A SMALL AMOUNT OF INTENSIFICATION AS THE SYSTEM
APPROACHES THE COAST, THE FORECAST CALLS FOR ABOUT 15 KNOTS OF
WEAKENING BEFORE REACHING KYUSHU DUE PRIMARILY TO DECREASING SSTS,
INCREASING VWS AND CONVERGENT FLOW PUNCHING IN FROM THE WEST. THE
SYSTEM WILL PASS OVER YAKUSHIMA ISLAND WITHIN THE NEXT HOUR OR TWO
AND THEN TAKE AIM AT THE WESTERN COAST OF KYUSHU, WITH A LANDFALL
EXPECTED TO THE SOUTH OF KAGOSHIMA BEFORE TAU 12. THE SYSTEM THEN
REACHES THE INFLECTION POINT OF THE RIDGE AXIS AND TURNS SHARPLY
NORTHEASTWARD, TURNING EAST PRIOR TO REACHING SASEBO. ONCE OVER
LAND, THE SYSTEM WILL CONTINUE TO RAPIDLY WEAKEN DUE TO THE
INFLUENCES NOTED ABOVE, WITH THE ADDED FACTOR OF LAND INTERACTION.
BY TAU 36, A STRONG COLD FRONT AND ASSOCIATED UPPER-LEVEL TROUGH
WILL LIE DRAPED ACROSS THE CENTRAL SEA OF JAPAN, MOVING QUICKLY
TOWARDS THE SOUTHEAST. TY 16W WILL BEGIN TO INTERACT WITH THIS
FRONTAL SYSTEM BY TAU 48, AND BE PUSHED A BIT TO THE SOUTH, MOST
LIKELY SOUTH OF THE JAPANESE ALPS, WHILE SLIDING NORTHEAST ALONG
AND AHEAD OF THE FRONT. LOW LEVEL WINDS FROM THE NORTH WILL BRING
COOL, DRIER AIR INTO THE BACKSIDE OF TY 16W, BLOWING OUT THE CORE
OF THE SYSTEM, COMBINING THE EFFECTS OF THE RUGGED TERRAIN TO
RAPIDLY WEAKEN THE SYSTEM DOWN TO 50 KNOTS OR LESS AS IT TRACKS
WEST OF TOKYO. THE REMNANT LOW ONCE KNOWN AS TY 16W WILL THEN
QUICKLY EXIT STAGE RIGHT AND MOVE NORTHEAST TO NEAR THE KURILS BY
TAU 96, ALL THE WHILE CONTINUING TO DISSIPATE. EXTRA-TROPICAL
TRANSITION (ETT) BEGINS AROUND TAU 48 AND WILL BE COMPLETE NO LATER
THAN TAU 96.
MODEL DISCUSSION: THERE HAVE BEEN NO SIGNIFICANT CHANGES IN THE
MODEL GUIDANCE SINCE THE PREVIOUS RUN. THE SCENARIO IS HANDLED IN
TWO DISTINCT WAYS, RESULTING IN TWO GROUPS OF MODELS. GROUP ONE
CONSISTS OF THE UKMET, UKMET ENSEMBLE AND GALWEM, WHICH BREAKS FROM
THE PACK AFTER TAU 36, REMAINS OVER THE SEA OF JAPAN AND
ACCELERATES THE SYSTEM TO OVER 30 KNOTS, PUSHING IT INTO THE
PACIFIC BY SHORTLY AFTER TAU 48. GROUP TWO CONSISTS OF THE GFS,
HWRF, ECMWF AND THEIR ENSEMBLES. THIS GROUP KEEPS THE SYSTEM MOVING
AT A SLOWER PACE, EXHIBITS MORE INTERACTION WITH THE FRONT AND
KEEPS THE TRACK A BIT FURTHER TO THE SOUTH. THE EXTREME OUTLIER
REMAINS THE ECMWF, WHICH DISSIPATES THE SYSTEM BY TAU 72 TO THE
SOUTH OF TOKYO. THE JTWC TRACK REMAINS CONSISTENT WITH THE PREVIOUS
FORECAST THROUGH THE FORECAST PERIOD, THOUGH CONFIDENCE REMAINS LOW
DUE TO THE EXTREME ALONG-TRACK SPREAD AFTER TAU 36. INTENSITY
GUIDANCE CONCURS ON THE SHARP WEAKENING TREND THROUGH THE FORECAST,
BUT THE JTWC FORECAST LIES ON THE HIGH EDGE OF THE ENVELOPE, WITH
ALL BUT HWRF INDICATING AN EVEN FASTER RATE OF WEAKENING, WITH
SEVERAL MODELS INDICATING DISSIPATION AS EARLY AS TAU 48.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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