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Atlantic Tropical Weather Discussion

AXNT20 KNHC 271716

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
116 PM EDT Thu Jul 27 2017

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 
1800 UTC.


An eastern Atlantic tropical wave extends along 31W from 04N to
17, moving west at 10 kt. Scattered moderate convection is noted 
from 07N to 12N between 30W and 35W. An 11Z scatterometer pass 
indicated sharp cyclonic turning at the intersection of the 
tropical wave and the monsoon trough near 09.5N31W, with winds
near 20 kt on the south side of the monsoon trough. Satellite
imagery also shows Saharan dust in wrapping into the northern 
side of the elongated circulation, contrasting with deep layer
moisture showing up south of 12N.

A central Atlantic tropical wave extends along 42W from 03N to 
16N moving west at 10 to 15 kt. No significant convection is
associated with this tropical wave other than a few showers where
it intersects the monsoon trough near 09N42W. This is due in part
to remnant dry Saharan air with the tropical wave, but also due to
subsident dry air in northerly flow aloft.

A tropical wave is along 59W/60W from 12N to 23N moving toward the
Lesser Antilles at 15 to 20 kt. The tropical wave is interacting 
with an upper low centered near 26N58W, and is much better
represented north of 18N as a result. The only convection is 
noted closer to the upper low, from 19N to 22N between 55W and 
60W. The tropical wave will move into the eastern Caribbean 
tonight, followed by moderate to fresh trade winds and a few 

A Caribbean tropical wave extends between Haiti and northeast
Colombia moving west at 15 to 20 kt. The tropical wave is moving
toward an upper low centered over central Cuba, and will start
interacting with the upper low through tonight, complicating
precise position analysis. No significant convection is associated
with the tropical wave, but its presence has allowed the pressure
gradient to relax and subsequently diminished the area of strong trade
winds across the central Caribbean. This wave will move across 
the rest of the Caribbean through tonight, and across the western 
Caribbean Sea Friday through Saturday.


The monsoon trough axis extends from 13N17W to 09N42W, where it
transitions to the intertropical convergence zone which reaches to
near Trinidad. No significant convection is noted other than what
was already mentioned in the tropical wave section above.



Weak ridging extends from central Florida to the Texas coast. A
trough is digging into north Florida, supporting scattered showers
and thunderstorms over the Big Bend area this morning. Another
line of showers and thunderstorms is observed from 26N83W to
24N90W, attributed to divergent flow aloft between an upper low
over central Cuba and an upper anticyclone farther north. A
similar configuration is supporting scattered moderate to isolated
strong convection off Veracruz in the southwest Gulf. The light to
gentle winds across the region are maintaining slight seas
overall. Little change is expected through Saturday for the 
majority of the Gulf. On Saturday, a weak front is forecast to 
drop south over the southeastern United States to near the Florida
panhandle by late Saturday may bring an increase of moisture 
along with an increase in shower and thunderstorm activity to the 
NE Gulf at that time.


Scattered showers and thunderstorms are diminishing over the
northern Caribbean north of 18N to the coast of Cuba, on the
periphery of an upper low centered over central Cuba. A large
cluster of convection is noted along the coast of Nicaragua, on
the southwest quadrant of an weak upper jet south of the upper
low. A few showers are noted across the Windward and Leeward
Islands moving into the eastern Caribbean, ahead of the tropical
wave moving into the region. Ridging north of the area continues 
to support fresh to locally strong trade across the Caribbean to 
the S of 17N and E of 82W, with the strongest winds along the 
coasts of northwest Venezuela and northeast Colombia, with the 
area of strong winds extending as far north as 15N.


Daytime heating is supporting scattered showers and thunderstorms
starting to form over the higher terrain of the island, on the 
eastern edge of an upper low centered over central Cuba.  
Moisture is expected to decrease on Friday and Friday night, then 
increase on Saturday as another tropical wave passes through the 
central Caribbean Sea.


The main weather maker in the western Atlantic continues to be the
upper low centered near 26N58W. As discussed in the tropical wave
section above, scattered showers and thunderstorms are active
south of the upper low from 19N to 22N between 55W and 
60W due to convergent trade winds in the lower levels and upper 
divergence. Scattered showers and thunderstorms are also ongoing
off northeast Florida, south of a stationary frontal boundary
situated just to the north off the Carolina coast. Scattered
showers are starting to develop across the Bahamas, on the
periphery of an upper low centered over Cuba. Weak surface 
ridging along 28N is supporting light to gentle breezes and slight
seas. Farther east, outside areas already discussed in the
tropical wave and monsoon trough/ITCZ sections, high pressure over
the central Atlantic is maintaining gentle to moderate trade
winds, with Saharan dust dominating east of 35W.

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