AXNT20 KNHC 281718

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
118 PM EDT Fri Jul 28 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 1200 UTC surface analysis and satellite imagery through 1715 UTC.


An eastern Atlantic tropical wave extends its axis from 17N37W to a 1012 mb surface low centered near 10N37W to 04N36W, moving westward at 10 kt. Both satellite imagery and the total precipitable water (TPW) imagery animation reveal that moisture has increased within the surrounding environment of this wave/low, and seems to have overtaken most of the Saharan dust that has been present over its northern portion over the past several days. Scattered showers are noted within 90 nm of the low circulation.

A central Atlantic tropical wave has its axis from 20N48W to 03N48W, moving west at 10 to 15 kt. This wave is moving through a very stable atmospheric environment marked by the presence of a very pronounced African Saharan Air Layer that covers the eastern and central Atlantic north of the tropics. Latest water vapor imagery confirms that strong subsidence and resultant dry air prevails over the the northern and central portions of this wave. Satellite imagery shows isolated showers east of the wave's axis south of 10N between 40W-45W.

An eastern Caribbean tropical wave has its axis along 66W, and extends northward to the Atlantic near 21N. Water vapor imagery depicts dry subsident air over the wave. No convection is occurring with this wave at this time. This wave will move across the remainder of the eastern Caribbean through tonight, then through the central Caribbean on Saturday.

A western Caribbean tropical wave has its axis along 80W south of 20N. The wave is moving west at about 15-20 kt. The southern portion of the wave is aiding scattered to numerous moderate convection over Central America and its adjacent waters. The wave will move across the rest of the western Caribbean through tonight and inland central America on Saturday.


The monsoon trough extends from 11N16W to 12N28W to the 1012 mb low at 10N37W. Aside from convection related to the tropical wave described above, scattered moderate convection is within 240 nm mainly east of 30W.



A surface ridge prevails across the basin anchored by a 1016 mb high centered near 26N92W. An upper-level low is centered over central Cuba enhancing convection across the Florida Peninsula, Florida Straits and western Atlantic mainly near the southern Bahamas. Scatterometer data depicts a light to gentle anticyclonic flow across the basin. Little change is expected through the weekend for the majority of the Gulf. On Saturday, a weak front is forecast to drop south over the southeastern United States to near the Florida panhandle by late Saturday may bring an increase of moisture along with an increase in shower and thunderstorm activity to the NE Gulf at that time.


Two tropical waves are moving across the basin. Refer to the section above for details on these features. Isolated showers are observed across the western Caribbean on the southern periphery of an upper-level low centered over central Cuba, as seen in water vapor imagery. Scattered to numerous moderate convection is noted over the southwest Caribbean south of 12N between 77W-83W. This activity is along the eastern extension of the Pacific monsoon trough that protrudes eastward to northwestern Colombia, and is being further aided by upper diffluent flow found on the southern extent of an upper trough located over the NW Caribbean that is associated with the aforementioned upper-level low. The present pressure gradient will allow for fresh to strong trades to continue over the south-central Caribbean through the weekend, with moderate to locally fresh trades prevailing elsewhere.


Fair weather prevails across the island at this time. Moisture should increase slightly tonight into Saturday as the present eastern Caribbean tropical wave passes through the central Caribbean. Some pockets of dry air behind the wave will follow in behind the wave.


Two tropical waves are moving across the basin. Refer to the section above for details. The upper-level low centered over central Cuba extends north enhancing convection across the southern Bahamas and Florida Straits. This activity is expected to linger into tonight, then begin to lift northward on Saturday in response to a frontal boundary that will push off the southeastern United States and move to the northwest portion on Saturday through Sunday. To the east, another upper- level low is reflected at the surface as a trough that extends from 32N56W to 25N57W. Isolated showers are observed along this trough. The remainder of the basin is under the influence of a surface ridge anchored by a 1024 mb high centered near 30N36W.

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