Tropical Weather Discussion
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AXNT20 KNHC 211735

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
135 PM EDT Sun May 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 1200 UTC surface analysis and satellite imagery through
1715 UTC.


Visible satellite animation suggests that a new tropical wave is
about to emerge off the coast of Africa. This wave will likely be
added to the 1800 UTC analysis/surface map.

A weak tropical wave is in the eastern Atlantic and extends from
12N31W to 04N32W, moving west at 10-15 kt. Based on current SAL
analysis from UW-CIMSS, african dust surrounds the wave. As a
result, only a few showers are noted near the wave axis.

A tropical wave is moving across the eastern Caribbean. Its axis
extends from 17N63W to NE Venezuela near 08N64W, moving west at
around 15 kt. Convection is limited in association with this wave.
The TPW animation shows a modest surge of moisture in the wake of
the wave axis.


The Monsoon Trough enters the tropical Atlantic through Sierra
Leone near 08N13W and continues to 07N21W. The ITCZ extends from
07N21W to 06.5N30W, then resumes west of a tropical wave at
06N35W to 05N45W to NE Suriname. Scattered moderate convection
is noted within about 120 nm of the african coast between 03N-
14N. Scattered moderate to isolated strong convection is from
07N-09N between 16W-18W.



Mosaic Doppler Radar from the SE U.S. shows numerous showers with
embedded tstms from SE Louisiana to the Florida Panhandle,
including also the NE Gulf. A surface trough is analyzed on the
1200 UTC map within this area and goes from 31N82W to 28N86W.
Scattered showers and tstms are also noted near the coast of Texas
and the NW Gulf in association with a stationary front. This
system is forecast to weaken near the northern Gulf coast in about
24-48 hours. Once again, areas of fog were observed over the NW
Gulf under the influence of a moist and warm SE wind flow. High
pressure of 1023 mb located over the western Atlantic near 31N72W
extends a ridge across Florida into the Gulf of Mexico. The
pressure gradient between the ridge and lower pressures across
Mexico and the far west Gulf waters is generally maintaining
moderate SE winds over the Gulf. Fresh winds were noted to the N
of the Yucatan Peninsula due to the presence of the thermal
trough. Gusty winds to near 30 kt are seen per buoy observations
near the convective activity over the NE Gulf. The ridge is
forecast to shift southward tonight through Tuesday as the weak
frontal boundary remains along the Northern Gulf Coast while
weakening. A stronger cold front will enter the NW Gulf by
Tuesday night.


Numerous moderate to isolated strong convection persists over the
SW Caribbean, particularly south of 12N. This convective activity
is associated with a northward displacement of the monsoon trough
that currently crosses parts of Costa Rica and Panama to a 1008 mb
low along the coast of Colombia near 11N76W. Upper-level diffluence
is also helping to induce this convective activity, that is
forecast to persist over the SW Caribbean and southern central
America for the next several days. A tropical wave is moving
across the eastern Caribbean. Please refer to the TROPICAL WAVE
section above for details. High pressure located near 31N72W
combined with the Colombian/Panamanian low is supporting fresh to
strong trade winds over the central Caribbean. Similar wind speeds
are also noted W of 85W, including the Gulf of Honduras. These
winds are expected to diminish tonight and Monday as the ridge
weakens in response to low pressure moving eastward from the
Eastern United States. Patches of low level moisture, embedded in
the trade wind flow, are observed elsewhere across the region. The
Saharan Air Layer from UW-CIMSS and visible satellite imagery
reveal the presence of african dust reaching the Lesser Antilles
and the far east Caribbean. Some of the islands are currently
reporting haze and dust.


Daytime heating, local sea breezes and mountain upslope lifting
will combine with available shallow moisture to produce some
cloudiness with scattered showers mainly during the afternoon and
early evening hours today and Monday. A tropical wave, now moving
across the eastern Caribbean, could enhance the shower activity
on Monday.


High pressure prevails across most of the Atlantic Ocean. As
previously mentioned, a 1023 mb high is located near 31N72W
while another high pressure center of 1025 mb is near 28N35W. The
latter one will move eastward to a position near 28N30W in about
24 hours. Moderate to fresh trades are seen per scatterometer data
across the tropical Atlantic west of 35W. A surface trough, likely
a reflection of an upper-level trough, extends from 28N56W to
21N62W. Scatterometer data combined with buoy observations
continue to show the wind shift associated with this trough.
Scattered moderate convection is within about 210 nm SE of the
trough from 23N-27N. A low appears to be forming along the trough
axis near 24N61W. This feature is ahead of an upper- level trough
that extends from 31N54W to the Mona Passage. Upper diffluence
ahead of the trough is helping to maintain the shower activity
ahead of the surface trough.

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