Wednesday, Jul 18, 2018

Atlantic Tropical Weather Discussion

National Hurricane Center - Tropical Weather Discussion (Atlantic)

  1. 071
    AXNT20 KNHC 181713

    Tropical Weather Discussion
    NWS National Hurricane Center Miami FL
    113 PM EDT Wed Jul 18 2018

    Tropical Weather Discussion for North America, Central America
    Gulf of Mexico, Caribbean Sea, northern sections of South
    America, and Atlantic Ocean to the African coast from the
    Equator to 32N. The following information is based on satellite
    imagery, weather observations, radar and meteorological analysis.

    Based on 1200 UTC surface analysis and satellite imagery through
    1630 UTC.


    SW Caribbean Sea gale warning: A gale goes into effect at July 19/0000
    UTC along the coast of Colombia from 11N to 13N between 73W and
    76W, with seas of 9 to 13 ft. The gale ends at 19/1200 UTC. Please
    read the High Seas Forecast, under the AWIPS/WMO headers
    HSFAT2/FZNT02 KNHC, for more details.


    A tropical wave is crossing the Cabo Verde Islands, with an axis
    extending from 20N24W to 04N25W, moving westward at 10 to 15 kt.
    A well defined 700 mb trough just west of the coast of western
    Africa is noted in the model guidance. A major outbreak of
    Saharan Air Layer (SAL) dust envelops the wave environment north
    of 10N as seen in GOES-16 images. As such, satellite imagery
    shows scattered moderate convection confined south of the SAL from
    07N to 10N between 20W and 29W.

    A central Atlantic tropical wave has an axis that extends from
    23N56W to 05N59W, moving westward at 15 to 20 kt. The wave is
    depicted on GOES-16 visible and RGB imagery as an inverted-V
    shape envelope of broken to overcast stratocumulus clouds covering
    the area. The wave is being intruded upon by Saharan dust
    limiting significant convection to scattered showers and isolated
    thunderstorms within 240 nm of either side of the wave.

    A tropical wave axis is over the western Caribbean that extends
    from 21N86W to S of Panama at 05N86W, moving westward at 15 to 20
    kt. Saharan dust is following in behind this wave axis as
    observed in GOES-16 satellite imagery. Scattered moderate to
    isolated strong convection is S of 12N W of 81W.


    The monsoon trough axis extends from W Africa near 18N16W to
    10N25W to 06N37W, where the ITCZ begins and continues to 05N51W.
    Aside from convection associated with the tropical waves discussed
    in the tropical waves section, scattered moderate convection is
    from 07N to 13N E of 20W, and from 06N to 11N between 29W and 35W.



    The western periphery of Atlantic high pressure ridging extends
    E to W over the central gulf waters. Light to moderate
    anticyclonic flow prevails over the region, outside of
    thunderstorms. A surface trough extends from 30N85W to 28N89W.
    Current NWS mosaic radar and satellite imagery show scattered
    thunderstorms over the northern gulf primarily north of 28N E of
    91W associated with this surface trough. This activity is also
    being enhanced by a mid- to upper- level trough over and to the NE
    of the area. The troughing and associated thunderstorm activity
    is expected to remain over this area for at least the next day or
    so. Weak high pressure is forecast to prevail across the central
    gulf waters through Thu night. Thereafter, a frontal trough will
    cross the NE gulf, forcing the ridge axis farther south over the
    SE Gulf. Increasing winds are expected over the NE gulf with this
    frontal trough in the area. Another surface trough will move
    westward off the Yucatan Peninsula the next few evenings,
    enhancing nocturnal winds over the eastern half of the SW Gulf.


    Please read the Special Features section for details about the
    pulsing gale force winds in the far SW Caribbean near the coast
    of Colombia. A tropical wave crossing the western Caribbean is
    discussed in the section above. Elsewhere, low-cloud streamers
    with brief isolated showers will continue over the far eastern
    Caribbean through Thu. Scattered showers and thunderstorms will
    develop over the interior sections of Hispaniola this afternoon
    and Thu afternoon. Mostly fresh E winds will continue over the
    central Caribbean Sea, and strong NE-E winds will be over the SW
    and S central sections of the Caribbean, through Thu.


    A mid- to upper-level trough over the SE United States is helping
    to enhance shower and thunderstorm activity NW of a line from
    31N72W to 25N80W. These thunderstorms will remain active through
    Thu as a portion of the trough moves off the eastern seaboard.
    High pressure will build in the wake of this trough late this week.
    A 1032 mb high well north of the area, centered near 40N40W is
    dominating much of the central and eastern Atlantic discussion
    waters. A large area of Saharan Air Layer (SAL) dust is currently
    over the central Atlantic from 10N to 25N and between 51W and
    66W, and over the eastern Atlantic S of 25N E of 51W. The dust
    will continue to translate westward for the rest of the week.

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