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Atlantic Tropical Weather Discussion

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

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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