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Atlantic Tropical Weather Discussion

AXNT20 KNHC 190453

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1253 AM EDT Thu Jul 19 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 0000 UTC surface analysis and satellite imagery through 
0515 UTC.


SW Caribbean Sea gale warning: A gale is in effect along the 
coast of Colombia from 11N to 13.5N between 72W and 77W, with 
seas of 9 to 13 ft. The gale ends on 19/1200 UTC. Please read the
High Seas Forecast, under the AWIPS/WMO headers HSFAT2/FZNT02 
KNHC, for more details.


A tropical wave is W of the Cabo Verde Islands, with an axis 
extending from 19N27W to 04N27W, moving westward at 10 to 15 kt. 
A well defined 700 mb trough near 09N27W is noted in 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 11N between 10W 
and 24W.

An E Caribbean tropical wave extends from 22N60W to 05N62W, 
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 
120 nm of either side of the wave. 

A tropical wave is over the Yucatan Peninsula and Central America  
from 20N90W to S of SE Mexico at 05N90W, moving westward at 15 to
20 kt. Saharan dust is following in behind this wave axis as 
observed in GOES-16 satellite imagery. Isolated moderate 
convection is within 240 nm of the wave axis. 


The monsoon trough axis extends from W Africa near 17N16W to 
08N30W to 06N40W, where the ITCZ begins and continues to South 
America near 05N52W. Aside from convection associated with the 
tropical waves discussed in the tropical waves section, widely 
scattered moderate convection is within 120 nm of the ITCZ axis W
of 43W.



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 over the NE Gulf from 
30N84W to 28N90W. Current NWS mosaic radar and satellite imagery 
show scattered thunderstorms over the northern gulf primarily 
north of 29N E of 91W associated with this surface trough. This 
activity is also being enhanced by an 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 W 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 are 
over the interior sections of Hispaniola and Cuba. 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 Sat. 


An upper-level trough over the SE United States is helping to 
enhance shower and thunderstorm activity NW of a line from 31N70W
to 27N77W. 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 42N37W 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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