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Atlantic Tropical Weather Discussion

AXNT20 KNHC 181157

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
757 AM 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 
1100 UTC.


SW Caribbean Sea gale warning: A gale goes into effect at 19/0000
UTC along the coast of Colombia from 11N to 12.5N between 74W and
76W, with seas of 10 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 nearing the Cabo Verde Islands, with an axis 
extending from 20N20W to 05N23W, moving westward at 10 to 15 kt. 
A well defined 700 mb trough exiting the coast of western Africa
is noted in the model guidance. Satellite imagery shows scattered
moderate convection from 07N to 10N between 17W and 28W. A major 
outbreak of Saharan Air Layer (SAL) dust envelops the wave 
environment north of 10N as seen in GOES-16 images.

A central Atlantic tropical wave has an axis that extends from 
22N54W to 06N56W, moving westward at 15 to 20 kt. The wave is 
depicted on GOES-16 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 from developing near it. Only scattered showers and 
isolated thunderstorms are seen within 240 nm of either side of 
the wave. 

A tropical wave axis is over the western Caribbean that extends 
from 22N82W to S of Panama at 06N81W, 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 20N16W to 
07N28W to 06N37W, where latest scatterometer data indicates that 
the ITCZ begins and continues to 06N37W to 10N55W. The ITCZ then
resumes west of a tropical wave at 09N58W and continues to South 
America near 08N62W. Aside from convection associated with the
tropical waves discussed in the tropical waves section, scattered
moderate convection is from 06N to 10N between 28W and 41W, and
from 01N to 05N between 41W and 48W.  



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. Current NWS mosaic radar and satellite imagery 
show scattered thunderstorms over the northern gulf primarily 
north of 28N E of 92W. This activity is being enhanced by a mid- 
to upper- level trough over and to the NE of the area. The base 
of the trough 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 northern 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 trough in
the area. Another surface trough will move westward off the 
Yucatan Peninsula the next few evenings, enhancing nocturnal 
winds over the eastern section 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. Aside from the tropical waves mentioned above, a 
small upper-level low is seen on water vapor imagery over the 
extreme northeastern part of the Yucatan Peninsula. 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. Low-cloud streamers with brief isolated 
showers will continue over the far eastern Caribbean through Thu. 
Scattered showers and thunderstorms will again develop over the 
interior sections of Hispaniola this afternoon and Thu afternoon.


A mid- to upper-level trough over the SE United States is helping
to enhance shower and thunderstorm activity NW of a line from
31N70W 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 1031 mb high well north of the area, centered near 38N41W 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 09N to 25N and between 51W and 65W,
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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