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Atlantic Tropical Weather Discussion

AXNT20 KNHC 211803

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
203 PM EDT Tue Aug 21 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
1745 UTC.


A tropical wave is just inland to just offshore the coast of 
Africa with its axis near 17W, moving westward at 10-15 kt. The 
wave is embedded within a very dry and stable environment. Only 
isolated moderate convection is occurring within 180 nm east of 
the wave axis from 11N to 14N.

A central Atlantic tropical wave has its axis extending from 
05N37W to 13N38W to 19N37W, moving westward at 10-15 kt. This wave 
is also embedded within a very dry and stable environment caused
by Saharan Air Layer outbreak migrating westward across the
central and eastern Atlantic. Only isolated moderate convection 
is noted within 60 nm either side of the wave axis from 10N to

A tropical wave over the eastern Caribbean has its axis from 
well inland Venezuela north-northeastward to 15N65W and to the
proximity of the Virgin Islands. It is moving westward near 
16 kt. Scattered moderate convection trails the wave from 09N
to 11N east to near 58W. 

A western Caribbean tropical wave has its axis extending along 
85W/86W and south of 21N, moving westward near 15 kt. Only 
isolated showers and thunderstorms are noted within 60 nm east of 
the wave.


The monsoon trough axis extends from coast of Senegal near 14N16W
to 10N23W to 09N31W and to 09N41W, where latest scatterometer data 
indicates that the  ITCZ axis begins and continues to 09N50W to 
09N60W. No significant convection is noted. Only isolated showers 
and thunderstorms are seen within 120 nm north of axis between 43W
and 48W.



Weak ridging reaches across the northern Gulf of Mexico along
roughly 27N, maintaining light to gentle breezes and 1 to 3 ft
seas. Gentle to moderate easterly flow is noted elsewhere south 
of the ridge. Latest NWS mosaic radar display shows isolated
showers and thunderstorms across much of the eastern part of the 
gulf, mainly due to a weak trough over that area. Scattered
showers and thunderstorms are observed over the far southwest 
section of the gulf in association with the Yucatan Peninsula 
trough that typically moves offshore across the southwestern gulf
late at night and into the morning hours, with the added factor 
of an upper-level low located just east of the coast of Mexico at 
22N97W. Expect for this convective activity to remain active 
through tonight. Otherwise, high pressure ridging will remain 
across the northern gulf waters, with the associated gradient 
producing gentle to moderate anticyclonic flow through Thu.


The pressure gradient across the area will maintain fresh to 
strong winds over the south central Caribbean off the coast of 
Colombia and across the Gulf of Venezuela through Thu. Moderate
to fresh trades will continue elsewhere through Thu. 

The tropical wave along 85W/86W will move across the rest of the 
western Caribbean this evening before moving inland Central
America. The tropical wave along 65W will move across the rest
of the eastern Caribbean  through Wed night and enter the eastern
part of the central Caribbean Thu.


Over the western Atlantic, a surface trough is analyzed from near
30N74W to the central Bahamas. An upper-level trough extends from
an upper-level low at 31N66W to the central Bahamas, and to 
central Cuba as a shear axis. Another trough extends from 32N59W 
to 27N68W, and another one extends from near 32N45W to 28N50W. A 
small surface trough extends from near 31N54W to 28N56W. With
these features in place along with a moist and unstable
environment, the result is scattered shower and thunderstorm
activity over the waters north of 24N between 60W and 75W, with 
the most concentrated activity observed north of 27N and 
between 70W and 76W. Isolated showers and thunderstorms are 
elsewhere west of 58W. A 1025 mb high center is analyzed north of
these troughs at 32.5N59W, with a ridge extending westward to
Bermuda, and southwestward from there to east-central Florida 
High pressure ridging will continue over the basin through the 
next several days. The trough extending across the central Bahamas
will continue westward through this evening. The aforementioned 
shower and thunderstorm activity is forecast to persist through 

Over the eastern part of the basin, a 1028 mb high is centered 
near 34N42W, supporting generally moderate north to northeast 
winds north of 20N. Saharan dust and associated dry air, as also
mentioned above under Tropical Waves, is noted mainly east of 
about 56W on GOES-16 Saharan Air Layer animation is inhibiting 
convection from developing across the eastern and central Atlantic

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