• Indian-S: STS Jobo W8

    From Weather Alert@1:2320/105 to All on Wed Apr 21 16:31:00 2021
    WTIO30 FMEE 211823
    RSMC / TROPICAL CYCLONE CENTER / LA REUNION
    TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)

    0.A WARNING NUMBER: 8/16/20202021
    1.A SEVERE TROPICAL STORM 16 (JOBO)

    2.A POSITION 2021/04/21 AT 1800 UTC:
    WITHIN 20 NM RADIUS OF POINT 9.8 S / 47.0 E
    (NINE DECIMAL EIGHT DEGREES SOUTH AND
    FORTY SEVEN DECIMAL ZERO DEGREES EAST)
    MOVEMENT: WEST 6 KT

    3.A DVORAK ANALYSIS: 3.0/4.0/W 1.0/6 H

    4.A CENTRAL PRESSURE: 985 HPA
    5.A MAX AVERAGE WIND SPEED (10 MN): 60 KT
    RADIUS OF MAXIMUM WINDS (RMW): 19 KM

    6.A EXTENSION OF WIND BY QUADRANTS (KM):
    28 KT NE: 95 SE: 335 SW: 220 NW: 95
    34 KT NE: 55 SE: 95 SW: 95 NW: 55
    48 KT NE: 35 SE: 35 SW: 40 NW: 35

    7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1009 HPA / 400 KM
    8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: DEEP

    1.B FORECASTS (WINDS RADII IN KM):
    12H: 2021/04/22 06 UTC: 9.7 S / 45.3 E, VENT MAX= 055 KT, SEVERE
    TROPICAL STORM
    28 KT NE: 75 SE: 155 SW: 150 NW: 100
    34 KT NE: 65 SE: 75 SW: 55 NW: 55
    48 KT NE: 45 SE: 30 SW: 35 NW: 35

    24H: 2021/04/22 18 UTC: 9.5 S / 43.8 E, VENT MAX= 045 KT, MODERATE
    TROPICAL STORM
    28 KT NE: 140 SE: 120 SW: 85 NW: 110
    34 KT NE: 65 SE: 55 SW: 20 NW: 100

    36H: 2021/04/23 06 UTC: 9.1 S / 42.6 E, VENT MAX= 040 KT, MODERATE
    TROPICAL STORM
    28 KT NE: 75 SE: 130 SW: 120 NW: 65
    34 KT NE: 65 SE: 55 SW: 45 NW: 35

    48H: 2021/04/23 18 UTC: 8.4 S / 41.3 E, VENT MAX= 030 KT, FILLING UP
    28 KT NE: 30 SE: 130 SW: 130 NW: 65

    60H: 2021/04/24 06 UTC: 7.8 S / 40.4 E, VENT MAX= 025 KT, FILLING UP

    72H: 2021/04/24 18 UTC: 7.4 S / 39.6 E, VENT MAX= 020 KT, REMNANT LOW

    2.B LONGER-RANGE OUTLOOK:
    NIL


    2.C ADDITIONAL INFORMATION:
    T=3.0+;CI=4.0+

    OVER THE LAST 6 HRS, JOBO'S CLOUD PATTERN CLEARLY DETERIORATED. THE
    LAST MODEL ANALYSIS SUGGEST A MODERATE MID-LEVEL NORTH-WESTERLY SHEAR
    THAT PUSHED DRY AIR CLOSE TO THE TC CORE. DEEP CONVECTION ONLY
    TRIGGERED AGAIN OVER THE SOUTHERN SEMI-CIRCLE IN THE LAST 2 HRS,
    PRODUCING AN ILL-DEFINED CDO PATTERN. SSMIS 1328Z AND 1519Z MW IMAGES
    CONFIRM THIS DISORGANISATION OF JOBO'S INTERNAL STRUCTURE WITH A FAR
    WEAKER CORE THAN ON PREVIOUS IMAGES. ONLY A PSEUDO-EYE REMAINS
    VISIBLE ON 85GHZ IMAGERY, BETWEEN TWO CONVECTION BANDS IN THE SOUTH
    AND THE NORTH.

    IN TERMS OF TRACK, JOBO HAS RESUMED A WESTWARD MOTION ON THE NORTHERN
    SIDE OF THE SUBTROPICAL HIGH GEOPOTENTIALS. AS IT WEAKENED, THE STORM
    FOUND A STRONGER STEERING FLOW AGAIN, WITHIN THE LOWER LEVELS OF THE TROPOSPHERE. TOMORROW, JOBO SHOULD CONTINUE WESTWARD BEFORE A
    NORTH-WESTWARD TURN LATER ON. THE DISPERSION AROUND THIS SCENARIO IS
    MODERATE. SOME TIMING DIFFERENCES REMAIN BETWEEN THE AVAILABLE MODELS
    BUT GFS AND IFS ARE NOW IN RATHER GOOD AGREEMENT.

    OVER THE NEXT 24H, THE AFOREMENTIONNED NORTH-WESTERLY SHEAR AT THE
    MID-LEVELS COULD KEEP ON HINDERING JOBO'S DEVELOPMENT. THE INTENSITY
    IS THUS EXPECTED TO REMAINS SOMEWHAT STATIONARY OR EVEN DECREASE A
    BIT. FROM TOMORROW EVENING, A WESTERLY SHEAR SHOULD APPEAR AT MID AND
    UPPER LEVELS AND TRIGGER A STRONGER WEAKENING. DRY AIR SHOULD ALSO BE
    MORE PRESENT FROM FRIDAY EVENING. JOBO'S SMALL SIZE MAKES IT VERY
    SENSIBLE TO ITS ENVIRONMENT, THUS INDUCING A GREATER UNCERTAINTY THAN
    USUAL ON THE INTENSITY FORECAST.

    POSSIBLE IMPACTS EXPECTED ON THE OUTER ISLANDS OF THE SEYCHELLES
    (ASTOVE, COSMOLEDO, ALDABRA) :
    -VERY INTENSE RAINFALL THAT COULD EXCEED 200 MM IN 24 HOURS.
    -STRONG WINDS (DEPENDING ON THE EXACT TRACK OF THE STORM): CYCLONIC
    CONDITIONS (GUSTS OVER 150 KM/H) CAN'T BE RULED OUT
    -DANGEROUS SEA CONDITIONS: WAVES EXCEEDING 6 METERS LOCALLY, STORM
    SURGE REACHING 30 TO 40 CM.
    BECAUSE OF JOBO'S SMALL SIZE, THE AREA AFFECTED BY SEVERE WEATHER
    CONDITIONS IS VERY NARROW, HENCE HIGH UNCERTAINTY ABOUT THESE
    IMPACTS.
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