Tropical Storm MEARI Advisory Thu Aug 11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (NINE) WARNING NR
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 28.6N 135.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 446 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY CONTINUES TO
SHOW A SOMEWHAT DISORGANIZED SYSTEM, THOUGH IT IS STEADILY
IMPROVING. THE PREVIOUSLY EXPOSED LOW LEVEL CIRCULATION CENTER
(LLCC) HAS SLID SOUTHEASTWARD AND APPEARS TO HAVE MERGED WITH, OR
WILL DO SO IMMINENTLY, WITH WHAT WAS A DEVELOPING AREA OF VORTICITY
TO THE SOUTHEAST SEEN IN MICROWAVE IMAGERY FROM SEVEN HOURS AGO. AT
THIS POINT, THE POSITION HAS TUCKED UNDER PERSISTENT CONVECTIVE
ACTIVITY, OBSCURING IT ONCE MORE. HOWEVER, TIMELY RECEIPT OF AN
111234Z ASCAT-B PASS REVEALED THAT THE LLCC REMAINS SLIGHTLY
ELONGATED, BUT HAS CONGEALED IN THE SOUTHEASTERN PORTION OF THE
BROADER ROTATION AND LENT HIGH CONFIDENCE TO THE INITIAL POSITION.
LIKEWISE, THE SCATTEROMETER DATA PROVIDED HIGH CONFIDENCE IN
NUDGING THE INTENSITY UP TO 35 KNOTS, A BIT HIGHER THAN THE
OBJECTIVE AND SUBJECTIVE FIXES WHICH RANGED BETWEEN 25-30 KNOTS, AS
IT SHOWED AN AREA OF 35-40 KNOT WINDS TO THE SOUTHEAST OF THE
CENTER. THE LLCC HAS TRACKED GENERALLY IN A COUNTER-CLOCKWISE LOOP
OVER THE PAST SIX HOURS WITH MOTION OF THE LAST THREE HOURS BEING
TO THE NORTH, BUT TRACK MADE GOOD SINCE THE PREVIOUS POSITION IS
ROUGHLY SOUTHEAST AT 2-3 KNOTS, AS IT MOVES ALONG THE WESTERN
PERIPHERY OF A DEEP SUBTROPICAL RIDGE (STR) TO THE EAST. THE
ENVIRONMENT IS CHARACTERIZED BY WARM (29-30C) SSTS, AND MODERATE TO
STRONG EQUATORWARD OUTFLOW. SHEAR ANALYSIS IS A BIT OF A DICHOTOMY,
WITH CIMSS AUTOMATED ANALYSIS SHOWING 5-10 KNOTS OF SHEAR, WHILE
HWRF FIELDS SUGGEST 25-30 KNOTS. CLEARLY THE SYSTEM IS EXPERIENCING
A FAIR AMOUNT OF SHEAR BASED ON THE SHARP NORTHERN EDGE OF THE
CONVECTIVE ENVELOPE AND CONTINUED STRUGGLE TO KEEP THE LLCC UNDER
THE CONVECTION, WITH AN ESTIMATED SHEAR VALUE OF 15-20 KNOTS.
INITIAL WIND RADII BASIS: SCATTEROMETER DATA
CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   CIMSS ADT: 28 KTS AT 1140Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
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: AFTER A PERIOD OF SOMEWHAT ERRATIC MOTION WITH
MULTIPLE VORTICES, NOW THAT THE LOW LEVEL CORE HAS STARTED TO
CONSOLIDATE, IT WILL SLOWLY START TO MOVE NORTH ALONG THE WESTERN
PERIPHERY OF THE STR TO THE EAST. AFTER TAU 24, THE SYSTEM WILL
ACCELERATE NORTHEASTWARD AS IT ROUNDS THE RIDGE AXIS AS THE
STEERING RIDGE SIMULTANEOUSLY SLIDES TO THE SOUTH-SOUTHWEST. TS 09W
IS FORECAST TO MAKE LANDFALL ALONG THE IZU PENINSULA BETWEEN TAUS
36 AND 48, MOVE THROUGH THE TOKYO METRO AREA THEN REEMERGE OVER
WATER SHORTLY AFTER TAU 48. WHILE TS 09W REMAINS UNDER A MODERATE
AMOUNT OF NORTHERLY SHEAR, IT HAS BEEN ABLE TO CONSOLIDATE A
SINGLE, MORE DEFINED LLCC OVER THE PAST SIX HOURS. HOWEVER, MODEL
GUIDANCE SUGGESTS THE SHEAR WILL HOLD FIRM FOR ANOTHER 12 TO 24
HOURS, AND UPPER-LEVEL DIVERGENCE IS EXPECTED TO DECREASE, THE
COMBINED EFFECT OF WHICH WILL BE TO INHIBIT SIGNIFICANT
INTENSIFICATION THROUGH THIS PERIOD, WITH THE SYSTEM ONLY FORECAST
TO REACH 40 KNOTS BY TAU 24. THE BRAKES START TO LET UP BY TAU 36
AS THE SYSTEM MOVES INTO A REGION OF LOWER SHEAR AND DIFFLUENT
UPPER-LEVEL OUTFLOW AHEAD OF A 200MB TROUGH. THE COMBINED EFFECTS
OF DECREASED SHEAR AND DRAMATICALLY IMPROVED OUTFLOW ALOFT SHOULD
ALLOW FOR A BRIEF PERIOD OF INTENSIFICATION, TO A PEAK OF 60 KNOTS
BY TAU 48 AS THE OUTFLOW OFFSETS THE SHEAR. THIS BURST OF
INTENSIFICATION WILL BE SHORT LIVED AND THE SYSTEM WILL BEGIN TO
RAPIDLY WEAKEN AFTER IT PEAKS AT TAU 48. AS IS THE CASE CURRENTLY,
THE SYSTEM IS EXPECTED TO REMAIN SOMEWHAT ASYMMETRIC THROUGHOUT THE
FORECAST, WITH THE HIGHEST WINDS EXPECTED TO BE IN THE EASTERN
HEMISPHERE OF THE CIRCULATION.  TS 09W WILL BEGIN EXTRA-TROPICAL
TRANSITION SHORTLY AFTER IT EMERGES BACK OVER WATER, AS IT MOVES
RAPIDLY NORTH-NORTHEAST AHEAD OF NEGATIVELY TILTED MAJOR SHORTWAVE
TROUGH AND ULTIMATELY BECOMES A VERTICALLY STACKED COLD CORE LOW
BETWEEN TAUS 72 AND 96 AS IT APPROACHES THE SOUTHERN KURIL ISLANDS.
MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE GUIDANCE REMAINS IN
GOOD OVERALL AGREEMENT ON THE TRACK, WITH ALL CONSENSUS MEMBERS
CONSTRAINED IN A TIGHT 65NM ENVELOPE AT TAU 48. AS THE SYSTEM MOVES
NORTHWARD AND BECOMES EXTRATROPICAL, MODEL SPREAD INCREASES TO A
MODEST 200NM. THE JTWC FORECAST REMAINS CONSISTENT WITH THE
PREVIOUS FORECAST, AND REMAINS ON THE EASTERN SIDE OF THE ENVELOPE
THROUGH THE FORECAST PERIOD, CLOSELY TRACKING THE HWRF THROUGH TAU
48. CONFIDENCE HAS IMPROVED DUE TO THE INCREASED CONFIDENCE IN THE
INITIAL POSITION BUT REMAINS MEDIUM THROUGH TAU 72 AND LOW
THEREAFTER. INTENSITY GUIDANCE REMAINS CONSISTENT WITH THE PREVIOUS
MODEL RUN, WITH THE DECAY-SHIPS STUBBORNLY STICKING TO THEIR
FORECAST OF LITTLE TO NO INTENSIFICATION, WHILE THE HWRF AND CTR1
RAPID INTENSIFICATION (RI) AID STILL PREDICTING A PEAK OF 65 KNOTS
AND 90 KNOTS RESPECTIVELY. THE CONSENSUS MEAN SITS AT A PEAK OF 50
KNOTS. THE DETERMINISTIC COAMPS-TC (CTCX) HAS COME ON BOARD WITH A
PEAK OF 70 KNOTS AT TAU 48 AND THE CTCX ENSEMBLE PROBABILISTIC
INTENSITY NOW SHOWS A RESPECTABLE 50 PERCENT CHANCE OF RI PRIOR TO
LANDFALL. WITH SUCH A LARGE SPREAD IN THE GUIDANCE, THERE IS LOW
CONFIDENCE IN THE INTENSITY FORECAST, WITH A POSSIBILITY OF A
SLIGHTLY HIGHER PEAK BETWEEN THE TAU 36 AND 48 FORECAST POINTS.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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