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Atlantic Tropical Weather Discussion

AXNT20 KNHC 220004

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
804 PM EDT Fri Sep 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 1800 UTC surface analysis and satellite imagery through 
2345 UTC.

...Special Features...

Showers and thunderstorms about 360 nm SSE of the Cabo Verde 
Islands are showing some signs of organization. This activity is 
associated with a tropical wave, analyzed along 18W from 03N-16N. 
A recent scatterometer pass shows a partially closed low-level 
circulation near 07N18W with winds of 25-30 kt in the eastern 
semicircle. Visible and IR satellite images depict a cluster of 
convection with a banding pattern from 04N-10N, between 16W-25W, 
where scattered moderate convection is noted. The environment is 
forecast to be conducive for slow development, and a tropical 
depression could form early next week while the system moves west 
around 15 kt across the low latitudes of the eastern and central 
tropical Atlantic Ocean. The system has now a medium chance of 
tropical cyclone formation within the next 48 hours.

A central Atlantic tropical wave has its axis along 52W between 
07N-17N moving WNW at 08 kt. The wave runs through a 1008 mb low 
near 13N52W. Shower and thunderstorm activity associated with a
these features has become better organized over the past few 
hours, and a tropical depression could form later tonight or 
Saturday. Strong upper-level winds and dry air are likely to 
prevent additional development of this system by late this weekend
while it moves west-northwestward to northwestward at around 10 
mph. 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 37W been relocated to 36W 
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 39W, or just ahead of the wave 
axis. Isolated showers are noted within 120 nm of the wave axis 
from 09N-13N. Little change is expected with this wave over the 
next 24-48 hours.

A central Caribbean Sea tropical wave has its axis along 80W. 
Movement is estimated to be westward around 10-15 kt. Scattered 
showers are noted west of Jamaica north of 15N between 78W-82W. A
maximum in TPW is noted just east of the wave axis.


The monsoon trough axis extends from the coast of Guinea near
10N14W to 07N18W to 07N27W. The ITCZ continues from 07N27W to 
08N40W to 10N56W to NE Venezuela. Other than convection 
associated with the tropical waves, isolated weak to moderate
convection is located within 60 nm south and 150 nm north of the
ITCZ between 40W-47W. Scattered moderate convection is also noted
over NE Venezuela as well as Trinidad and Tobago. 



An upper-level cyclonic circulation is moving slowly westward 
over the far eastern Gulf and the west coast of Florida. Satellite
imagery and NWS Doppler Radar indicate scattered showers and 
thunderstorms over the eastern Gulf, mainly from 24N-29N, between 
81W-87W, including portions of the Florida Keys and the Florida 

A ridge extends from a high pressure over the eastern U.S. to the
northern Gulf of Mexico. 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 Sat.


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

The eastern Pacific monsoon trough combined with diffluence aloft
is helping to induce scattered showers and thunderstorms over
portions of Costa Rica, Nicaragua and eastern Honduras. Plenty of 
moisture will persist over the southwest Caribbean through 
Saturday as the tropical wave, currently along 80W, reaches the 
area and moves inland into central America late Sat or early Sun.

The pressure gradient between central Atlantic high pressure and 
the lower pressure near the central Caribbean tropical wave will 
support fresh trades today. Winds will diminish over most of the 
Caribbean Sea this weekend.


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

A cold front extends from a 1011 mb low just SE of Bermuda and 
enters the forecast area near 31N63W and extends westward to 
28N70W to 27N75W. Isolated showers are noted along the frontal 
boundary. The front will drift slightly southward today, then 
dissipate by Saturday morning. The low is currently producing 
moderate to fresh winds north of 28N between 60W-65W. 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 ridge, anchored by a 1022 mb surface high located near 

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