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Atlantic Tropical Weather Discussion

AXNT20 KNHC 220606

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
206 AM EDT Sat Sep 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 0000 UTC surface analysis and satellite imagery through 
0515 UTC.

...Special Features...

The well defined low east of the Windward Islands has developed
into Tropical Depression Eleven, centered near 13.1N 53.4W at 
22/0300 UTC, or 440 nm E of the Windward Islands, moving WNW at 5
kt. Estimated minimum central pressure is 1007 mb. Maximum 
sustained wind speed is 30 kt with gusts to 40 kt. See latest NHC 
forecast/advisory under AWIPS/WMO headers MIATCPAT1/WTNT31 KNHC 
for more details.

A low pressure system is located at about 550 miles south- 
southeast of the Cabo Verde Islands. Although the low is currently
producing only limited shower and thunderstorm activity, the 
system appears to have become better organized today and a 
tropical depression could form during the next day or two. This 
system is expected to move westward at 15 to 20 mph across the low
latitudes of the eastern and central tropical Atlantic Ocean 
through early next week. The system has now a medium chance of 
tropical cyclone formation within the next 48 hours. Please refer 
to the latest Tropical Weather Outlook under AWIPS/WMO headers 
MIATWOAT/ABNT20 KNHC for more information.

A 1010 mb non-tropical low is located near 30N64W, or about 850 
miles west-southwest of the Azores. Conditions are expected to be
conducive for the low to acquire subtropical or tropical 
characteristics, and a subtropical or tropical cyclone is likely 
to form early next week while the low meanders over the central 
Atlantic Ocean. The system has now a medium chance of tropical 
cyclone formation within the next 48 hours. Please refer to the 
latest Tropical Weather Outlook under AWIPS/WMO headers 
MIATWOAT/ABNT20 KNHC for more information.


The tropical wave has its axis along 38W from 04N-16N and is 
moving west at 10-15 kt. The wave corresponds nicely with a 
maximum in TPW imagery. Model analyses depict an associated 700 mb
trough along 38W. Isolated showers are noted within 120 nm of the
wave axis from 10N-13N. Little change is expected with this wave 
over the next 24-48 hours.

A western Caribbean Sea tropical wave has its axis along 82W,
moving west at 10-15 kt. This wave is well depicted in model
guidance and TPW imagery shows abundant moisture in its
environment. Scattered showers are noted within 75 nm on either
side of the wave's axis. 


The monsoon trough extends across Africa along 17N. The trough
begins over the Atlantic near 07N21W to 07N36W. The ITCZ begins
near 07N40W to 10N52W. Scattered showers are noted within 75 nm
north of the ITCZ between 43W-52W. 



An upper-level cyclonic circulation centered near 28N85W is 
enhancing convection across the eastern half of the basin mainly
east of 90W. A surface trough was analyzed from 27N88W to 23N88W.
Another trough is located from 27N82W to 24N82W. Surface ridging 
prevails across the remaining of the basin. The ridge will 
support gentle to moderate easterly winds and seas 3 ft or less 
across most of the Gulf of Mexico through the middle of next week.
It is possible that a typical nocturnal surface trough, that will
be moving westward across the southwestern corner of the Gulf of 
Mexico, may produce locally fresh winds through Saturday.


A tropical wave is moving across the western Caribbean. Please 
see the Tropical Waves section for more details.

The eastern Pacific monsoon trough combined with diffluence aloft
is helping to induce scattered showers over portions of Costa 
Rica and Panama. Plenty of moisture will persist over the 
southwest Caribbean through Saturday as the tropical wave, 
currently along 82W, moves west through the weekend. The pressure
gradient between central Atlantic high pressure and the lower 
pressure near the west Caribbean tropical wave will support 
moderate to fresh trades across the area. Winds will diminish over
most of the Caribbean this weekend.


Currently, there are two tropical waves and a tropical depression
between the west coast of Africa and the Lesser Antilles. Please 
see the Special Features/Tropical Waves sections for more details.

A weakening frontal boundary extends from a 1010 mb low near 
30N64W to 27N68W. Minimal convection is observed along the 
frontal boundary. The front will dissipate by this morning. The 
low is currently producing moderate to fresh winds north of 27N 
between 60W-66W. The low is expected to drift south and then west
over the forecast area between 60W-70W while weakening. The 
remainder of the Atlantic forecast area is under the influence of 
a surface ridge, anchored by a pair of 1017 mb highs centered near
24N63W and 24N47W. 

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