Tropical Weather Discussion
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AXNT20 KNHC 121736

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
136 PM EDT Sat Aug 12 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
1715 UTC.


A low pressure of 1012 mb is centered near 23N68.5W. Scattered
moderate convection is noted from 21N-25N between 64W-68W. Dry
air aloft and unfavorable upper-level winds have limited
significant development during the past few days. This morning, the
low has become a little better defined and the shower activity
has increased somewhat since yesterday. This system continues to
show some signs of organization, but there is no evidence of a
closed surface circulation. Conditions remain conducive for
development, and a tropical depression could form during the next
day or two. The low is forecast to move northwestward and
northward through the weekend, and then turn to the northeast away
from the United States early next week. There is a medium chance
for tropical cyclone formation during the next 48 hours.


A tropical wave is in the far eastern Atlantic just west of the
Cabo Verde Islands moving west at about 20 kt. It axis extends
from 20N25W to 08N26W. The wave shows up very well on the TPW
animation and 700 mb streamline analysis. Scattered moderate
convection is noted where the wave meets the monsoon trough from
08N-13N between 25W-28W.

Another tropical wave in the central Atlantic is near 46W from
08N to 20N, moving W at 15-20 kt. The wave coincides with a well
defined 700 mb trough, and a high amplitud northward bulge of
moisture is noted on the TPW product. African dust surrounds the
wave, which is limiting the associated convective activity. Only
isolated moderate convection is seen near the southern end of the
wave axis.

A tropical wave is in the central Caribbean and extends from
eastern Cuba through Jamaica to near 10N77W. The wave coincides
with a 700 mb trough, and is well depicted in the moisture
product. Scattered showers are noted over the southwest Caribbean
in the vicinity of this wave.


The monsoon trough extends from the coast of African near 14N17W
to 13N20W to 11N30W to 09N40W to 08N47W. The Intertropical
Convergence Zone continues from 08N47W to the coast of South
America near 08N59W. Aside from convection associated with the
tropical waves, scattered moderate convection is noted from 10N-
15N E of 21W, and from 07N to 10N between 28W-35W. Isolated
moderate convection is from 07N to 10N between 38W and 50W.



A 1018 mb high pressure is centered over the NE Gulf of Mexico
near 26N88W. Light to gentle anticyclonic flow is observed over
the Gulf waters, with the exception of moderate winds noted west
of a thermal trough moving off the Yucatan into the southwest
Gulf. The high pressure center will be nearly stationary across
the NE and north-central Gulf waters through the weekend. Then,
the ridge is forecast to shift early next week allowing fresh
southerly return flow to set up over the western Gulf Tue and Wed.

A thermal trough will develop each evening over the Yucatan
Peninsula, shifting westward into the southwest Gulf during the
overnight hours, and dissipating over this area each morning.
Locally higher winds can be expected west of the trough axis.


A tropical wave is moving through the central Caribbean. See
Tropical Waves section for details. The tropical wave will
continue to propagate westward, moving west of the area late
Sunday night. Fresh to locally strong winds prevail over the
south central Caribbean, while gentle to moderate winds are
blowing elsewhere. These general conditions will persist through
the weekend. The pressure gradient is forecast to tighten early
next week as the Atlantic ridge builds westward. This will allow
for the trade winds to expand northward across the central
Caribbean to near 17N by Monday morning. Expect building seas to
8-10 ft with the strongest winds across the south-central

Clusters of moderate to isolated strong convection are noted over
the SW Caribbean, just west of a 1012 mb low pressure located
within the monsoon trough near 10N79W. A diffluent pattern aloft,
associated with an upper-level anticyclonic circulation situated
near 12N79W supports this convective activity. Shallow moisture
embedded in the trade wind flow is noted elsewhere.


An upper-level trough extending just north of Hispaniola and
through Windward Passage to Jamaica will combine with the local
effects to favor the development of scattered showers and tstms
mainly during the afternoon and evening hours today. Moisture is
forecast to diminish across the island on Sunday. Expect isolated
showers and tstms due to local effects as daytime heating, local
sea breezes and mountain upslope lifting.


Please see the tropical wave section above for more on the
tropical waves moving across the Atlantic waters. Also, please see
above in the Special features section for more on low pressure,
and the potential for tropical cyclogenesis, over the southwest
north Atlantic waters. A weak surface trough persists across the
central Atlantic and extends from 31N46W to 27N53W. Isolated
showers are near the trough axis. The Bermuda-Azores high
will strengthen over the central Atlantic this weekend. The
pressure gradient will tighten between the area of high pressure
and the tropical wave currently over the eastern Atlantic this
weekend. This will freshen winds north of the tropical wave by
Sunday as the wave propagates westward. The Saharan Air Layer
tracking product from CIMSS indicates abundant african dust between
the two tropical waves currently located across the tropical

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