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Atlantic Tropical Weather Discussion

AXNT20 KNHC 221648

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1248 PM EDT Sun Jul 22 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 
1530 UTC.


A tropical wave is off the coast of Africa extending from 09N to
20N along roughly 18N/19N, moving W at 10-15 kt. A large area of
Saharan dust is noted along the wave north of 10N. Farther south,
scattered moderate convection is noted where the tropical wave 
intersects the monsoon trough off the coasts of Sierra Leone and 
Guinea, from 07N to 10N east of 10W.

A tropical wave is in the central Atlantic with axis extending 
from 09N-22N along 41W/42W, moving W at 15-20 kt. This tropical 
wave continues to be on the leading edge of a large area of 
Saharan dry air and dust, inhibiting large scale convection at 
this time. Isolated cells are noted on the southern end of the 
tropical wave where it intersects the monsoon trough and 
intertropical convergence zone.

A tropical wave is in the western tropical Atlantic with axis 
extending from 09N-23N along 54W, moving W at 10-15 kt. The
tropical wave is accompanied by Saharan dry air and dust,
inhibiting large scale convection. However the northern extent of
the tropical wave will be coming into phase with a broad upper
trough to the northwest of the wave axis. This may allow
development of isolated convection later today or tonight 
approximately 300 nm northeast of the Leeward Islands.

A low amplitude and low latitude tropical wave is moving across
the Pacific coast plains of Colombia, from 01N-11N along roughly
75W. The tropical wave may be interacting with overnight drainage
flow to support a large area of showers and a few thunderstorms 
off the Pacific coast of Colombia and in the Gulf of Panama. 

A tropical wave extends from the Gulf of Honduras into the eastern
Pacific along roughly 87W. No significant convection is noted in
the Caribbean related to this tropical wave.


The monsoon trough axis extends from the coast of Mauritania near
18N16W to 08N30W. Segments of the intertropical convergence zone 
reach from 08N30W to the coast of Guyana near 07N59W. Scattered 
moderate to isolated strong convection is noted from 07N to 10N 
east of 10W.



A surface trough moving across the Florida Big Bend area in the 
far northeast Gulf may be a focus for a few showers and 
thunderstorms later today. the northern portion of a tropical wave
over the western Yucatan peninsula will move into the southwest
Gulf later today, then continue west of the area through Mon. 
Otherwise, 1017 mb high pressure centered over the west central 
Gulf near 24N92W is maintaining fair weather, light to gentle 
winds, and 1 to 3 ft seas. 

The surface trough over the northeast Gulf will be followed by a 
weak cold front that will move over the north-central and
northeast Gulf waters early this week. This front will become 
stationary and weaken to a trough by Thu. A surface trough will 
move off the Yucatan Peninsula into the Bay of Campeche each 
evening, accompanied by fresh nocturnal winds. Elsewhere, a ridge 
will prevail.


The northern portion of a tropical wave will is moving across the
far southwestern Caribbean today, just north of Panama. This may
bring increased showers and thunderstorms especially tonight, from
the central coast of Panama to Costa Rica. Dry conditions persist
elsewhere, and no significant shower or thunderstorm activity is
observed. Earlier scatterometer pass indicated fresh to strong
trade winds over the south central Caribbean, mainly off Colombia.
Maximum seas are estimated to be 8 to 10 ft. Seas are 3 to 5 ft in
the northwest Caribbean, and 5 to 7 ft elsewhere. A tropical wave
is approaching 55W. While Saharan dry air and dust are inhibiting
showers and thunderstorms, there may be isolated showers at least
in the Windward Islands by late Mon as the tropical wave moves
into the region. Little change is expected elsewhere.


Scattered showers and thunderstorms are ongoing over the northern
Bahamas, related to divergent flow aloft. Another cluster of
thunderstorms is emerging off the northeast Florida coast, ahead
of a deep layer trough moving through the region. Gusty winds are
possible with these thunderstorms. A third area of thunderstorms
is brewing farther east, about 180 nm northeast of the central
Bahamas, in part also related to divergent flow aloft but also
related to a weak boundary on the tail end of a weakening front
north of the area. Moderate S to SW winds are noted west of 70W
with 4 to 6 ft seas in open waters. For the forecast, the 
Atlantic high pressure along with the low pressure system over 
the southeast U.S. will continue to produce moderate to fresh 
southerly winds across the waters just offshore the central and
northeast Florida through Wed. Moderate to fresh winds are also 
expected south of 22N, including approaches to the Windward 
Passage. Ridging will dominate the area most of the forecast 
period, with a surface trough reaching the E part of the region by

Farther east, scattered showers and thunderstorms are noted north
of 27N between 55W and 65W, related to a broad cold-core mid to
upper level low centered near 29N60W. Elsewhere fair weather
persist with moderate to fresh NE to E winds and 6 to 8 ft seas north
of 20N, and gentle to moderate trades farther south into the 
tropics with 5 to 7 ft seas.

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