Tropical Weather Discussion
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AXNT20 KNHC 210604

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
203 AM EDT Fri Jul 21 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 0000 UTC surface analysis and satellite imagery through
0515 UTC.


A tropical wave over the far eastern Atlantic has its axis
extending from near 18N30W to 03N30W, moving west at 20 kt. This
wave is along the leading edge of a deep pool of moisture off the
coast of Africa. The METEOSAT-9 imagery along with the Total
Precipitable Water imagery show an extensive area of Saharan dry
air and dust NW of the wave. The GFS guidance continues to show am
well-defined 700 mb trough with this wave. Scattered moderate
convection is from 09N-14N between 26W-31W.

A large amplitude tropical wave is over the central Atlantic with
axis from 24N52W to 08N53W, moving west at 15 kt. The Total
Precipitable Water imagery animation depicts deep moisture south
of 24N between 47W-58W. Scattered moderate to isolated strong
convection is from 03N-12N between 41W-49W. A portion of this
wave is forecast to move across the eastern Caribbean during the
upcoming weekend, bringing increasing moisture and probabilities
for scattered showers and thunderstorms with gusty winds.

A tropical wave is over the E Caribbean with axis from 19N63W to
08N64W, moving west at 20 kt. SSMI Total Precipitable Water
imagery shows only a slightly moist area from 10N-20N. There is a
well defined 700 mb trough associated with this wave. Scattered
showers are within 120 nm of the wave axis. This wave is capable
of producing strong gusty winds as it moves west across the
eastern Caribbean tonight and into Friday morning, and across the
central Caribbean on Saturday and Saturday night.

A tropical wave is over the central Caribbean Sea with axis
from 17N79W to Panama at 06N79W. This wave is the remnants of
former Tropical Storm Don. Abundant low level moisture is S of
17N. A well defined 700 mb trough is also present. Scattered
moderate to strong convection is along the coast of Nicaragua
from 11N-17N between 80W-89W. The wave will move across the rest
of the central Caribbean tonight, and across the western Caribbean
on Friday. Strong gusty winds will continue to be possible with
the associated shower and thunderstorm activity.

A tropical wave is in the W Caribbean with axis extending from
22N87W to the E Pacific near 05N89W, moving W at 10-15 kt. SSMI
TPW imagery depict abundant moisture associated with this wave.
The wave is however, in a region of unfavorable wind shear, and
Saharan dry air and dust are affecting the western periphery of
the wave environment. Numerous strong convection is over S
Guatemala, El Salvador, and the E Pacific from 07N-15N between


The monsoon trough extends from 17N16W to 10N35W. The ITCZ then
extends from 10N35W to 10N50W. Aside from the convection
associated with the tropical waves, scattered moderate convection
is along the coast of W Africa from 08N-13N between 14W-18W.
Scattered moderate to isolated strong convection is along the ITCZ
from 03N-12N between 45W-49W.



A surface trough is over the Yucatan Peninsula from 22N90W to
16N91W. Scattered showers are within 60 nm of the trough axis. A
1018 mb high is centered over the NW Gulf of Mexico near 28N93W.
5 kt anticyclonic winds are noted around the high. The NE Gulf
has 5-10 kt S flow. Radar imagery shows isolated showers over the
NE Gulf, and N Florida. In the upper levels, a small upper level
low is centered over Mexico near 23N100W. Another small upper
level low is centered over the Yucatan Peninsula near 21N91W. A
third small upper level low is centered over N Florida near
29N93W. Expect in 24 hours for the third upper level low to move
to move to the N central Gulf, with convection. In addition,
expect scattered showers and thunderstorms to form over Florida
and the N Gulf N of 23N during maximum heating Friday.


The main features in the basin are the now three tropical waves
moving through the basin. See the section above for details.
Scattered showers and isolated thunderstorms are seen over the far
SW Caribbean within 120 nm of the coasts of Costa Rica and
Panama due to the proximity of the monsoon trough that currently
extends along 10N. Mostly fair weather conditions are observed
elsewhere, with areas of Saharan dust spreading westward across
much of the waters mainly north of about 15N.


Dry air and dust aloft have moved in over the Caribbean north of
15N including Hispaniola supporting fair weather. A tropical wave
currently over the far eastern Caribbean will pass just to the
south of the island during the next 24 hours. Moisture associated
with this wave may help erode some of the dry air in place as it
advects towards the island leading to increase chances for
scattered showers and isolated thunderstorms across the island.


Two tropical wave are moving through the far southern waters. See
the Tropical Waves section above for details. Scattered showers
are over the N Bahamas and the W Atlantic, N of 25N and W of 73W,
due to a surface trough. A large 1030 mb high is centered over
the E Atlantic near 40N32W with ridge axis extending SW to 28N70W.
Of note in the upper levels, a small upper level lows is over the
W Atlantic at 25N73W enhancing showers. Another upper level low
is also centered over the central Atlantic near 29N47W enhancing
showers W of center.

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