Atlantic hurricane map

Thursday, Sep 20, 2018

Atlantic Tropical Weather Discussion

National Hurricane Center - Tropical Weather Discussion (Atlantic)

  1. 007
    AXNT20 KNHC 201452 AAA
    TWDAT

    Tropical Weather Discussion...Updated
    NWS National Hurricane Center Miami FL
    1052 AM EDT Thu Sep 20 2018

    Updated Caribbean section for SW Caribbean convection

    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 0600 UTC surface analysis and satellite imagery through
    1400 UTC.

    ...TROPICAL WAVES/TROPICAL TROUGHS...

    A far eastern Atlantic tropical wave has its axis along 21W/23W
    from 05N25N to 14N24W to 20N23W, moving westward at 10 to 15 kt.
    This wave is supported by a 700 mb inverted-trough from 14N to
    20N. om 20N southward. This wave is associated with a distinct 700
    mb trough from 13N to 20N. In addition, mid-level satellite
    winds show winds veering in direction from NE to SE across the
    wave axis. The total precipitable water (TPW) satellite animation
    shows a well-depicted plume of moisture trailing the wave to the
    coast of Africa.

    A far eastern Atlantic surface trough is analyzed from 10N31W to
    19N30W, moving westward at about 10 kt. The trough continues
    to be reflected at 700 mb as a rather distinct inverted trough.
    700 mb trough. No deep convection is seen with the trough, only
    isolated showers and thunderstorms within 60 nm either side of the

    A 1010 mb low, formerly a tropical wave, is analyzed near 10N48W,
    moving westward at 10 to 15 kt. The overall cloud pattern of this
    low appears more symmetric than 18 to 24 hours ago. Satellite
    imagery shows scattered moderate to strong convection within 120
    nm of the low in the northern semicircle. Scattered moderate
    convection is within 90 nm of the low in the southern semicircle.
    Latest NHC Tropical Weather Outlook calls for some development
    of this system today before before upper-level winds become
    highly unfavorable for tropical cyclone formation starting tonight
    and continuing through the weekend.

    An eastern Caribbean Sea tropical wave has its axis along 69W
    south of 20N to inland Venezuela at 09N. It is moving westward at
    10 to 15 kt. Satellite imagery shows a rather large area of
    scattered showers showers and thunderstorms east of the wave north
    of 15N and between the wave and 65W. The TPW animation concurs
    with this shower and thunderstorm activity in depicting low-level
    over the eastern Caribbean Sea. Satellite imagery indicates some
    Saharan dust in the wake of the wave over the far eastern
    Caribbean Sea and tropical Atlantic between the Lesser Antilles
    and 55W. The dust is forecast to continue to spread westward,
    across the eastern Caribbean Sea islands, bringing hazy skies and
    stable conditions through early Sat.

    ...MONSOON TROUGH/ITCZ...

    The monsoon trough axis extends off the coastal sections of
    Senegal near 13N17W to 12N21W. The ITCZ axis extends from 10N24W
    to 08N33W to 06N44W. Scattered moderate convection is noted from
    04N to 10N between 11N and 20W, and within 180 nm south of the
    ITCZ between 28W and 31W. Scattered moderate convection is to the
    northwest of the ITCZ within 60 nm of line from 09N51W to 09N60W.

    ...DISCUSSION...

    GULF OF MEXICO...

    A cyclonic shear axis is observed on water vapor imagery to
    stretch from the NW Bahamas to S Florida, westward to near
    26N85W, and northwestward to near 29N90W. Cyclonic flow covers
    the eastern gulf south of this shear axis, while strong easterly
    upper-level flow around the southern periphery of an anticylone
    anchored over far northwestern Georgia. Between 90W and 94W, the
    upper flow is anticyclonic from a weak anticyclone centered at
    24N93W. W of 94W, the upper flow becomes broadly cyclconic in
    advance of an upper-level trough that is moving eastward across
    Texas and extends to the far eastern section of Mexico. The
    trough is moving through a very moist and unstable atmosphere.
    Scattered showers and isolated thunderstorms are over the far
    western gulf from 21N to 28N west of 95W. Mid and upper-level
    clouds associated with this activity are streaming northeastward
    west of 94W.

    A surface trough, remnants of former tropical cyclone Isaac, is
    located over the Yucatan Peninsula. No deep convection is noted.
    Earlier overnight scattered shower and thunderstorm activity
    observed over the eastern Bay of Campeche has weakened as the
    typical nocturnal Yucatan Peninsula trough has progressed
    westward across the eastern Bay of Campeche this morning.
    Isolated showers and thunderstorms are over the Bay of Campeche
    and waters adjacent to the Yucatan Peninsula.

    A weak surface trough is analyzed over the southeastern Gulf of
    Mexico from near Naples to near 22N88W. Isolated showers are
    near the trough from 22N to 24N bewteen 83W and 85W.

    Isolated showers and thunderstorms are over the remainder of the
    gulf waters.

    The forecast calls for high pressure to build across the eastern
    United States through tonight. The associated gradient will
    bring gentle to moderate east to southeast winds and 2 to 4 ft
    seas across the basin through Sun. The surface trough over the
    eastern Yucatan Peninsula will weaken as it gradually moves
    westward across the remainder of the Yucatan Peninsula through
    tonight.

    CARIBBEAN SEA...Updated

    A mid to upper-level central Atlantic trough axis stretches
    southwestward to a small cyclonic circulation over the Windward
    Passage, to 15N76W and to near 13N79W. Isolated showers and
    thunderstorms are just northeast of Jamaica from within 60 nm of
    18N76W. Isolated showers and thunderstorms are seen from north
    of 16N and west of 79W.

    An eastern Caribbean Sea tropical wave, with axis along 69W,
    will move westward, across the central Caribbean Sea through Fri
    and into Central America on Sun. Scattered showers and
    thunderstorms east of the wave north of 15N and between the wave
    and 65W may be attendant by strong gusty winds and at times
    rough seas. This activity is underneath an upper anticyclone
    that should help sustain it through Fri even with the wave
    axis translating westward. The extreme northern edge of this
    activity is approaching the far southwest side of Puerto Rico
    and the Mona Passage.

    The gradient associated with high pressure building from the
    central Atlantic to the central Bahamas will support moderate to
    fresh trade winds and building seas across the entire basin from
    late on Wed through Fri.

    The eastern segment of Pacific monsoon trough protrudes into the
    far southwestern Caribbean Sea. With this feature there, and
    combined with the already low-level speed convergence in place
    there, this presently leading to increasing scattered moderate
    to strong convective clusters over the waters southwest of a
    line from near 13N83W to 12N80W to 11N76W. This activity is
    likely to remain active into this evening.

    Scattered showers and thunderstorms are approaching the lower
    Windward Islands over the waters just east of Trinidad and
    Tobago.

    ATLANTIC OCEAN...

    A narrow mid-upper trough is indicated by the models and
    observed in water vapor imagery extends from near 32N70W
    southwestward to 27N75W, where it transitions to a cyclonic
    shear axis to S Florida, and continues well into the
    southeastern Gulf of Mexico. To the east and southeast of this
    trough, a deep-layer trough extends from near 32N61W to 26N63W
    and to a small cyclonic circulation over the Windward Passage.
    A surface trough is analyzed from near 32N61W to near 30N63W.
    Also at the surface, a cold front extends from a 1004 mb low
    (gale center) located well north of the area at 33N68W,
    southwestward to 32N71W and to near 29N80W. Surface observations
    and satellite imagery suggest that a surface trough may be
    forming from near 27N68W to just east of the SE Bahamas.
    Isolated showers and thunderstorms are seen from 24N to 28N
    between 65W and 71W, while scattered showers and thunderstorms
    are along and within 60 nm south of the cold front between 70w
    and 79W. Similar convection is within 30 nm either side of a
    line from 23N69W to 25N65W to 27N61W, and also north of 29N
    between 58W and 63W, where upper dynamics are more robust.

    Over the eastern Atlantic, a broad upper-level low is observed
    near 28N37W, with a trough axis stretching southwestward to
    29N48W and to a base near 13N57W. A cyclonic shear axis extends
    east-northeastward from the upper-low to 30N29W and continues
    northeastward as an upper trough to an ill-defined small upper-
    level low that is seen in water vapor imagery near 32N23W.
    A mid and upper-level trough is over the far eastern Atlantic
    along a position from near 24N22W to a small upper-level
    circulation at 20N23W and to base near 12N29W. Broad upper-level
    anticyclone is observed between this trough and the trough
    related to the aforementioned broad upper-level low. At the
    surface, the remnant low of former tropical cyclone Joyce is
    analyzed near 29N31W with a pressure of 1014 mb. Latest
    satellite imagery shows broken low and mid-level clouds with
    possible isolated showers within 90 nm of the low in the NE
    semicircle and 60 nm of the low in the SE semicircle. The recent
    trends in the satellite imagery indicate that this low is
    weakening further, and most likely will be a trough later today.
    A pair of 1021 mb high are analyzed. The first one is anchored
    near 30N49W, and the second one is just north of the area near
    33N37W. The surface analysis depicts high pressure covering the
    area north of 23N from 40W to 60W.

    The aforementioned cold front is forecast to move southeastward
    to the waters north of 27N through Fri before it dissipates. The
    1004 mb gale center north of the area is forecast to weaken
    as it moves southeastward to near 34N62.5W by early Fri. The
    attendant cold front will also weaken through Fri. The low will
    also weaken as it moves to near 31N67W by Fri evening. It is
    then forecast to drift westward and slowly weaken Sat through
    Sun. NE swell will move into the open waters east of the Bahamas
    Fri through early parts next week.

    For additional information please visit
    http://www.hurricanes.gov/marine

    $$
    Aguirre