• Indian-S: Bongoyo W7

    From Weather Alert@21:1/175 to All on Mon Dec 7 20:33:00 2020
    WTIO30 FMEE 071819
    RSMC / TROPICAL CYCLONE CENTER / LA REUNION
    TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)

    0.A WARNING NUMBER: 7/3/20202021
    1.A MODERATE TROPICAL STORM 3 (BONGOYO)

    2.A POSITION 2020/12/07 AT 1800 UTC:
    WITHIN 20 NM RADIUS OF POINT 15.4 S / 79.9 E
    (FIFTEEN DECIMAL FOUR DEGREES SOUTH AND
    SEVENTY NINE DECIMAL NINE DEGREES EAST)
    MOVEMENT: WEST-SOUTH-WEST 11 KT

    3.A DVORAK ANALYSIS: 3.0/3.0/D 0.5/6 H

    4.A CENTRAL PRESSURE: 994 HPA
    5.A MAX AVERAGE WIND SPEED (10 MN): 40 KT
    RADIUS OF MAXIMUM WINDS (RMW): 65 KM

    6.A EXTENSION OF WIND BY QUADRANTS (KM):
    28 KT NE: 75 SE: 280 SW: 335 NW: 75
    34 KT NE: 0 SE: 75 SW: 185 NW: 0

    7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1008 HPA / 700 KM
    8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: MEDIUM

    1.B FORECASTS (WINDS RADII IN KM):
    12H: 2020/12/08 06 UTC: 16.8 S / 78.0 E, VENT MAX= 040 KT, MODERATE
    TROPICAL STORM
    28 KT NE: 55 SE: 250 SW: 205 NW: 75
    34 KT NE: 45 SE: 75 SW: 95 NW: 65

    24H: 2020/12/08 18 UTC: 17.9 S / 77.0 E, VENT MAX= 040 KT, MODERATE
    TROPICAL STORM
    28 KT NE: 55 SE: 205 SW: 185 NW: 75
    34 KT NE: 45 SE: 55 SW: 85 NW: 65

    36H: 2020/12/09 06 UTC: 18.8 S / 76.4 E, VENT MAX= 035 KT, MODERATE
    TROPICAL STORM
    28 KT NE: 45 SE: 130 SW: 165 NW: 75
    34 KT NE: 35 SE: 100 SW: 75 NW: 65

    48H: 2020/12/09 18 UTC: 19.2 S / 75.4 E, VENT MAX= 035 KT, MODERATE
    TROPICAL STORM
    28 KT NE: 45 SE: 215 SW: 110 NW: 75
    34 KT NE: 35 SE: 85 SW: 45 NW: 65

    60H: 2020/12/10 06 UTC: 19.3 S / 73.8 E, VENT MAX= 030 KT, TROPICAL
    DEPRESSION
    28 KT NE: 35 SE: 95 SW: 120 NW: 55

    72H: 2020/12/10 18 UTC: 19.2 S / 71.8 E, VENT MAX= 025 KT, FILLING UP

    2.B LONGER-RANGE OUTLOOK:
    96H: 2020/12/11 18 UTC: 18.7 S / 65.6 E, VENT MAX= 025 KT, REMNANT
    LOW


    2.C ADDITIONAL INFORMATION:
    T=CI=3.0-

    DURING THE LAST 6 HOURS, THE BONGOYO CLOUD CONFIGURATION HAS EVOLVED
    FROM A CURVED BAND CONFIGURATION TO A SHEARED CONFIGURATION TO
    FINALLY BECOME A CDO PATTERN WHOSE CENTER IS LOCATED AT THE EASTERN
    EDGE OF THE CDO. THIS EVOLUTION IS CERTAINLY RELATED TO A MODERATE
    WINDSHEAR OF THE MIDDLE TROPOSPHERE ACCOMPANIED BY AN INTRUSION OF
    DRY AIR WHICH WEAKENED THE CONVECTION. THIS HAS BROKEN THE CONVECTIVE
    CENTER OF THE CURVED BAND STILL PRESENT FURTHER EAST OF THE SYSTEM.
    THE DVORAK ANALYSIS CAN BE REVISED SLIGHTLY UPWARDS WITH A CI OF 3.0
    LEAVING WINDS OF THE ORDER OF 40KT VALIDATED LOCALLY BY THE 1531UTC
    ASCAT SWATH.

    LIMITED CHANGE IN THE PHILOSOPHY OF THE TRACK FORECAST: BONGOYO
    MAINTAINS A SOUTHWEST TRACK UNDER THE INFLUENCE OF THE SUBTROPICAL
    RIDGE FURTHER SOUTH. WITH THE PASSAGE FURTHER SOUTH OF A TROUGH, THE SUBTROPICAL RIDGE INDUCES A LESS MARKED DIRECTIONAL FLOW: THE TRACK
    SLOWS DOWN AND TAKES ON A MORE MARKED MERIDIONAL COMPONENT BY MIDDAY
    ON TUESDAY. IN MID-WEEK, A NEW SUBTROPICAL RIDGE IS POSITIONED
    SOUTHWEST OF BONGOYO AGAIN IMPOSING A WESTWARD TRACK WHICH
    ACCELERATES.

    DURING THIS DISPLACEMENT, BONGOYO SEEMS TO HAVE FINISHED BENEFITING
    FROM ITS FAVORABLE WINDOW, WITH THE REINFORCEMENT OF THE CONSTRAINT
    IN THE MIDDLE TROPOSPHERE. THIS CONSTRAINT WILL GRADUALLY LIMIT THE
    DEVELOPMENT OF THE SYSTEM ON TUESDAY. ON WEDNESDAY, THE DEEP VERTICAL
    SHEAR SHOULD ALSO INCREASE AND BE ASSOCIATED WITH GREATER DRY
    INTRUSIONS. THE SYSTEM SHOULD THEN RAPIDLY EVOLVE INTO A REMNANT LOW
    AS IT MOVES TOWARDS THE MASCARENE ISLANDS.
    =
    --- SBBSecho 3.11-Linux
    * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (21:1/175)