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Atlantic Tropical Weather Discussion

AXNT20 KNHC 181713

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
113 PM EDT Wed Jul 18 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 1200 UTC surface analysis and satellite imagery through 
1630 UTC.


SW Caribbean Sea gale warning: A gale goes into effect at July 19/0000
UTC along the coast of Colombia from 11N to 13N between 73W and 
76W, with seas of 9 to 13 ft. The gale ends at 19/1200 UTC. Please
read the High Seas Forecast, under the AWIPS/WMO headers 
HSFAT2/FZNT02 KNHC, for more details.


A tropical wave is crossing the Cabo Verde Islands, with an axis 
extending from 20N24W to 04N25W, moving westward at 10 to 15 kt. 
A well defined 700 mb trough just west of the coast of western 
Africa is noted in the 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 10N between 20W and 29W.

A central Atlantic tropical wave has an axis that extends from 
23N56W to 05N59W, 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 240 nm of either side of the wave. 

A tropical wave axis is over the western Caribbean that extends 
from 21N86W to S of Panama at 05N86W, moving westward at 15 to 20
kt. Saharan dust is following in behind this wave axis as 
observed in GOES-16 satellite imagery. Scattered moderate to 
isolated strong convection is S of 12N W of 81W. 


The monsoon trough axis extends from W Africa near 18N16W to 
10N25W to 06N37W, where the ITCZ begins and continues to 05N51W. 
Aside from convection associated with the tropical waves discussed
in the tropical waves section, scattered moderate convection is 
from 07N to 13N E of 20W, and from 06N to 11N between 29W and 35W.



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 from 30N85W to 28N89W. 
Current NWS mosaic radar and satellite imagery show scattered 
thunderstorms over the northern gulf primarily north of 28N E of 
91W associated with this surface trough. This activity is also 
being enhanced by a mid- to 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 western 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 will 
develop over the interior sections of Hispaniola this afternoon 
and Thu afternoon. 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 Thu. 


A mid- to upper-level trough over the SE United States is helping
to enhance shower and thunderstorm activity NW of a line from
31N72W to 25N80W. 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 40N40W 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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