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Atlantic Tropical Weather Discussion

AXNT20 KNHC 211749

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1249 PM EST Thu Nov 21 2019

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 
1720 UTC.


Tropical Storm Sebastien is centered near 23.5N 60.5W at 21/1500 
UTC, or about 352 nm NNE of the northern Leeward Islands, moving 
NNE at 7 kt. Estimated minimum central pressure is 999 mb. Maximum
sustained wind speed is 55 kt with gusts to 55 kt. Numerous 
moderate with scattered strong convection is within 240 nm of the 
center in the SE quadrant. Scattered moderate with isolated strong
convection is elsewhere within 250 nm E semicircle. Sebastien is 
expected to begin a faster northeastward motion during the next 
few days. Sebastien is forecast to become a hurricane by tonight 
but a weakening trend is expected to begin by late Friday. The 
system is likely to become an extratropical cyclone by Saturday. 
Public Advisories for Sebastien are available via AWIPS/WMO 
headers MIATCPAT5/WTNT35 KNHC. Forecast/Advisories for Sebastien 
are available via AWIPS/WMO headers MIATCMAT5/WTNT25 KNHC.


An Atlantic Ocean tropical wave is along 49W from 13N southward, 
moving W at 10-15 kt. Scattered showers are seen along the wave
axis from 06N-09N between 48W-50W.

A Caribbean Sea tropical wave is along 77W from 18N southward, 
moving W at 10 kt. Isolated showers are near the wave axis from 


The monsoon trough passes through the coast of Sierra Leone near 
09N13W to 08N14W. The ITCZ continues from 08N14W to 03N30W to 
07N48W, then continues W of a tropical wave near 07N50W to the
coast of Suriname near 05N55W. Scattered moderate convection is
seen along the ITCZ from 01S to 06N between 26W-35W. 


Mid to upper-level anticyclonic wind flow spans the Gulf of 
Mexico, along with surface ridging from a 1027 mb high anchored in
the Mid-Atlantic. Little to no precipitation can be seen across 
the basin. Latest scatterometer data depicts fresh to strong 
southeasterly return flow is occurring over the western Gulf of 
Mexico with gentle to moderate easterly winds observed in the 
eastern Gulf.

A surface ridge will prevail across the area through Friday, with
fresh SE return flow persisting over the western Gulf. A cold 
front will move off the Texas coast and into the NW Gulf Friday 
night, cross the northern and central waters this weekend, then 
weaken and stall over the southern Gulf Sunday night. 


A cold front passes through western Haiti near 19N74W and 
stretches westward to northern Jamaica to the NW Caribbean near 
20N84W. Isolated showers are seen along the front with scattered 
thunderstorms seen along the Mona Passage and in southern 
Dominican Republic. A surface trough is analyzed over the Gulf of 
Honduras from 16N88W to the Yucatan near 19N88W. Scattered showers
are occurring near this feature. Subsidence is seen across the 
eastern and western Caribbean and inhibiting any convective 
activity. Latest scatterometer data depicts fresh northerly winds 
in the Windward Passage, with gentle to moderate trades elsewhere.

The cold front will continue moving over the northern Caribbean 
through tonight, then stall and weaken on Friday. Fresh NE winds 
will prevail across much of the western Caribbean through Friday,
with the strongest winds expected through the Windward and Mona 
passages as high pressure builds behind the cold front. Easterly 
trades will freshen across the south-central Caribbean early next 


For information on T.S. Sebastien, see Special Features section

A cold front enters the forecast area in the central Atlantic 
near 31N59W and stretches to northern Haiti near 20N71W. This 
boundary combined with the moisture from T.S. Sebastien is giving 
way to numerous showers along and ahead of the front from 25N-31N 
between 54W-62W. Meanwhile, there is an upper level low near 
19N42W with a surface trough associated with it analyzed from 
09N44W to 17N40W. Scattered showers with isolated thunderstorms 
are seen from 07N-24N between 29W-41W. A cold front is dipping 
southward toward the Cabo Verde Islands, stretching from a 1004 mb
low near 34N15W to 30N29W. Otherwise, surface ridging continues 
to dominate the rest of the basin from a 1025 mb high near 31N38W.

A surface trough is hugging the Florida coast from 25N80W to
30N80W with no significant weather associated with it. Latest
scatterometer data depicts fresh to strong N winds behind the cold
front, mostly N of 21N and between 61W-74W.  

Tropical Storm Sebastien will strengthen to a hurricane while 
accelerating northeastward away from the forecast waters tonight. 
The cold front will continue moving eastward and steer Sebastien 
into the central Atlantic. High pressure will build behind the 
cold front across the northern waters through Saturday, then 
shift eastward Saturday night. Another cold front will cross the 
region Sunday through Monday.