Tropical Weather Discussion
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AXNT20 KNHC 202348

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
747 PM EDT Sun Aug 20 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 1800 UTC surface analysis and satellite imagery through
2315 UTC.

A tropical wave extends along 76W/77W moving W at 15-20 kt. The
remnant circulation of Harvey continues to be analyzed as
a 1006 mb low pressure along the wave axis near 14N77W with
scattered to numerous showers and thunderstorms occuring from 15N-
21N between 74W-79W, and from 12N-16N between 77W-81W. This shower
and thunderstorm activity has changed little in organization
since earlier today. An Air Force Reserve Unit Hurricane Hunter
aircraft investigating the remnants of Harvey found that the
system still lacks a well-defined center of circulation, and so
far there is no indication of winds to tropical storm force.
Gradual development of this system is possible, and it could
become a tropical cyclone once again while it moves west-
northwestward across the northwestern Caribbean Sea, near the
northern coast of Honduras, during the next day or two. The system
is expected to reach Belize or the Yucatan Peninsula on Tuesday.
Interests in northern Nicaragua, Honduras, Belize, and the Yucatan
Peninsula should monitor the progress of this system. Regardless of
development, the wave and associated low pressure (remnants of
Harvey) will continue to impact the central Caribbean tonight and
the western Caribbean Monday and Tuesday. The main concern will be
heavy rainfall, with the potential of flash flooding and mudslides
over parts of Nicaragua and Honduras. This system and associated
shower and tstm activity will continue to affect Jamaica, the
Cayman Islands, and parts of Cuba tonight and Monday, then
reaching Belize and the Yucatan peninsula by late Monday.

A tropical wave is added to the 1800 UTC analysis/surface map and
extends from 21N19W to 10N21W. The Hovmoller Diagram shows the
westward propagation of the wave. In addition, this wave in a
moist area based on TPW imagery and has a well pronounced 700 mb
trough. Scattered moderate convection is noted where the wave
meets the monsoon trough from 11N-13N between 19W-22W. A 1008 mb
low pressure is analyzed ahead of the wave near 14N24W and it is
forecast to move westward, in tandem with the wave, over the next
24-48 hours. Saharan dust is noted ahead of the wave axis and
west of the Cabo Verde Islands.

A tropical wave extends from 19N52W to 10N54W moving W at 15-20
kt. The wave shows up very well on the TPW animation and 700 mb
streamline analysis. The northern portion of the wave has
fractured and is analyzed as a surface trough extending from
25N48W to 20N50W. No significant deep convection is associated
with the wave itself, however scattered moderate convection is
occurring mainly east of the surface trough from 19N-24N between
46W and the trough axis.

A tropical wave is reaching the Yucatan peninsula and Belize and
extends from 19N87W across Honduras into the Eastern Pacific
region to near 10N87W moving W at 15-20 kt. Subtle troughing is
noted on 700 mb streamline analysis, but abundant moisture is
observed on either side of the wave axis based on the TPW animation.
The wave, combined with a diffluent pattern aloft, is generating
scattered showers and thunderstorns over parts of the Yucatan
peninsula, Belize and northern Guatemala, as well as over parts
of Honduras, Nicaragua and El Salvador.

The monsoon trough extends from the African coast near 13N17W to
10N24W to 08N38W. Sattered moderate convection is from 11N-13N
between 19W-22W, and within about 120 nm S of the monsoon trough
between 33W-36W.


A large and well defined upper-level low centered over the eastern
Gulf near 25N87W continues to generate scattered showers and
thunderstorms, mainly over the SE Gulf and western Cuba, icluding
also parts of the Florida peninsula. A surface trough, reflection
of this upper-level low is analyzed over south Florida and the
Florida Keys to western Cuba near 22N84W. The western half of the
Gulf is under the influence of a weak ridge, anchored by a 1019
mb high pressure centered over the State of Alabama. Isolated
showers and light to gentle anticyclonic winds prevail W of 90W.
The upper-low will drift westward reaching the central Gulf on
Monday. This system will continue to enhance the development of
showers and tstms across the Gulf waters on Monday. Looking
ahead, the remnant low of Harvey, currently moving across the
Caribbean Sea is expected to reach Belize or the Yucatan Peninsula
on Tuesday, and then move into the Bay of Campeche by the middle
of the week, where redevelopment appears more likely.

The primary area of concern across the Caribbean Sea is the low
pressure (remnants of Harvey) that is generating scattered to
numerous showers and thunderstorms over the central Caribbean.
Please, see Special Features section for more details. A tropical
wave is exiting the area, with axis along 87W. Please, see the
Tropical Waves section for details. A trough of low pressure
located across the Atlantic waters, north of Puerto Rico,
combined with abundant tropical moisture supports the development
of showers and strong thunderstorms across parts of Puerto Rico
and Hispaniola this afternoon and evening. This trough and
associated moisture will move away from Puerto Rico on Monday,
but will continue to enhance the shower and tstm activity over

Daytime heating, local sea breezes, and mountain upslope lifting
will combine with available moisture to produce scattered showers
and thunderstorms across the island mainly during the afternoon
and evening hours. A trough of low pressure, currently located
north of Puerto Rico will be north of Hispaniola on Monday, and
will bring increased moisture, cloudiness, and precipitation to
the island.

As previously mentioned, a trough of low pressure is north of
Puerto Rico and extends from 26N67W to 20N68W. This system
continues to produce disorganized showers and thunderstorms, with
fresh to strong winds mainly on its northeast side based on
scatterometer data. Environmental conditions are expected
to be unfavorable for development of this system during the next day
or two, but they could become slightly more conducive for development
by midweek when the system is near the northwestern Bahamas or
Florida. This feature is expected to move west-northwestward at
15-20 kt during the next few days. A pair of tropical waves are
between the coast of Africa and the Lesser Antilles, and a another
surface trough extends 25N48W to 20N50W. Please, see the Tropical
Waves section for details. The remainder of the Atlantic is under
the influence of a ridge, with a center of 1022 mb located SW of
Bermuda near 31N68W. This high pressure center is forecast to
remain nearly stationary over the next 24 hours. Another 1023 high
pressure center is seen near 31N42.5W.

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