Atlantic Tropical Weather Discussion

National Hurricane Center - Tropical Weather Discussion (Atlantic)

  1. 000
    AXNT20 KNHC 270003

    Tropical Weather Discussion
    NWS National Hurricane Center Miami FL
    805 PM EDT Mon Jun 26 2017

    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 1800 UTC surface analysis and satellite imagery through
    2315 UTC.


    A tropical wave axis is along 26W from 01N to 11N, moving
    westward at 15 kt. The wave is embedded within a rather moist
    environment, however Saharan dry air and dust is intruding some
    around the northern segment of the wave s surface ridging noses
    south just to the west of the wave. Only widely scattered
    moderate to isolated moderate convection is present within 120
    nm either side of the axis from 07N to 10N. This activity
    appears to be on the decreasing trend.

    A broad tropical wave with axis is along 46W from 01N to 11N,
    moving westward at 10-15 kt. The wave is in a region of
    favorable wind shear. It is also within a moderate moist
    environment and under an area of diffluent flow aloft that is
    located between an upper anticyclone near 15N51W and mid/upper
    ridging to the southeast of the wave. In addition 700 mb
    streamline analysis also supports a wave signal near that of the
    surface position. Scattered moderate isolated strong convection
    is seen within 180 nm east of the axis from 06N-08N, within 180
    nm west of the axis from 10N-11N and within 60 nm west of the
    wave from 07N-08N.

    A tropical wave is over the central Caribbean axis along 69W/70W
    south of 19N to inland Venezuela near 08N69W, moving westward at
    15-20 kt. The wave is in a region of unfavorable wind shear and
    in a limited moist environment. Deep convection that develops
    near and along the wave axis is observed to have a short
    duration due to the moderate to strong westerly winds aloft.
    Scattered moderate isolated strong convection is seen within
    30 nm of a line from 17N71W to 17.5N74W. Scattered showers and
    isolated weak thunderstorms are elsewhere within 120 nm west
    of the axis from 14N-17N. Isolated showers are within 60 nm
    east of the wave axis.

    A tropical wave is over the western Caribbean with axis along
    86W south of 21N to the northwest section of Costa Rica, moving
    westward at about 15 kt. The southern portion of the wave is
    very near the eastern Pacific monsoon trough that extends across
    the SW Caribbean Sea. The wave marks the leading edge of deep
    tropical moisture that trails the wave east to near 78W.
    Clusters of scattered moderate isolated strong convection are
    located within this area of deep moisture south of 17N to inland
    northern Honduras between the wave axis and 83W, and also south
    of 16N between 77W and the coast of central America. The
    activity south of 16N between 77W and the coast of central
    America is mainly associated with the monsoon trough. This wave
    is forecast to move inland early on Tuesday.


    The Monsoon Trough axis extends from the coast of Africa near
    15N17W southwest to near 05.5N25W. The Intertropical Convergence
    Zone axis then begins just to the west of the tropical wave
    along 26W near 05N28W, and continues to 06N37W to 05N45W.
    05N52W. Scattered moderate isolated strong convection is within
    180 nm south and 60 nm north of the axis between 41W-43W.



    A broad upper level trough extends from over the eastern United
    States seaboard southwest to the extreme northeast portion of
    the Gulf, then becomes a narrow trough south to near 24N85W.
    This feature supports a stationary front that is analyzed from
    just offshore NE Florida southwest to Cross City and to 29N86W,
    and northwest from there to inland southeastern Louisiana.
    Widely scattered showers and isolated thunderstorms are noted
    along, and within 60 nm south of the boundary west of 88W.
    Isolated showers are elsewhere within 30 nm of the boundary.
    The boundary is forecast to gradually become diffuse through
    Tuesday afternoon, with the remnants possibly lifting back north
    as a warm front. The portion of the front along the Florida
    coast may sag some to the south through Tuesday as high pressure
    to its north builds in from the northwest.

    Upper level anticyclonic wind flow covers the rest of the Gulf
    of Mexico, especially from the area of the upper level trough,
    southwestward to over SW portion of the area. A pair of surface
    troughs are analyzed over the SW and far western portions of the
    Gulf. One surface trough extends from just east of southern
    Texas to 21N96W and southeast to near 18N94W. Scattered showers
    and isolated thunderstorms are noted within 90 nm east of the
    trough south of 23N, while isolated showers are within 60 nm to
    its west south of 23N. The second surface trough extends along
    93W from 20N-26N. Scattered moderate isolated strong convection
    is within 120 nm east of this trough from 22N-24N, and also
    within 60 nm west of the trough from 21N-23N. A weak pressure
    pattern is present elsewhere.


    The main features in the basin are two tropical waves already
    discussed in the waves section above. Aside from the shower and
    thunderstorm activity associated with them as described above,
    latest scatterometer data depicts fresh to strong winds in the
    vicinity of the waves south of about 17N. These winds are
    expected to increase to near gale across the Gulf of Venezuela
    on Tuesday night. Otherwise, scattered showers and thunderstorms
    are developing over the Windward Passage and just north of
    Jamaica. Isolated showers in streamer fashion are observed over
    the eastern Caribbean, and over portion of the northwest
    Caribbean north of the shower and thunderstorm activity
    associated with the tropical wave along 86W. A broad tropical
    wave currently over the central tropical Atlantic is expected to
    enter the eastern Caribbean Sea on Tuesday night, and reach the
    central Caribbean late on Wednesday. This wave will be
    accompanied by scattered showers and thunderstorms, some of
    which may contain gusty winds.


    Upper level moderate to strong southwest to west winds continue
    to advect deep level moisture over Hispaniola and surrounding
    waters as the northern portion of a tropical wave moves across
    the far eastern part of the island this evening. With these
    factors in play and in addition to the presence of ample
    instability as well, expect scattered showers and thunderstorms
    to be on the increase over much of the island through the next
    day or so.


    Surface high pressure covers the basin, with the parent 1025 mb
    anticyclonic center located just north of the area at 33N47W.
    A broad upper trough along the United Stated eastern seaboard
    supports a stationary front that extends from a 1016 mb low
    pressure center near 32N79W southwest to inland NE Florida. A
    short-wave trough riding along the southern periphery of the
    upper trough in combination with the surface boundary is
    activating increasing clusters of scattered moderate isolated
    strong convection over the far northwest portion of the basin to
    inland NE Florida. This activity is expected to continue quite
    active through late Tuesday as the surface boundary begins to
    drift southward, and upper level dynamics provide further
    support to maintain it active.

    A large upper level cyclonic circulation is situated over
    the central Atlantic 28N57W, and is slowly moving northwestward.
    Isolated showers and thunderstorms are noted north of 24N
    between 52W-63W. Similar activity is to its west within 30 nm of
    a line from 28N66W to 32N69W. Another upper level cyclonic is
    moving south-southwest over the eastern portion of the basin
    near 28N26W. Isolated showers and thunderstorms are possible
    within 120 nm of the southeast quadrant of the low. Otherwise,
    isolated showers and thunderstorms are evident elsewhere west of
    about 50W. They are moving in a general westward motion. Stable
    and rather stable atmospheric conditions are present to the east
    of 50W under stronger high pressure.

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