Tropical Weather Discussion
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AXNT20 KNHC 221737

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
137 PM EDT Mon May 22 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.


The tropical wave that came off the west African coast yesterday
now extends from 12N18W to 05N19W. Scattered moderate convection
is where the wave meets the ITCZ/Monsoon trough, mainly from
04N-08N between 17W-23W. The TPW animation shows a decent surge
of moisture near the wave axis.

A weak tropical wave extends from 12N36W to 05N37W, 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 Caribbean Sea. Its axis
extends from eastern Dominican Republic to near Aruba in the ABC
Islands, moving west at around 15 kt. Convection is limited in
association with this wave. The TPW animation shows a modest surge
of moisture near the wave axis.


The Monsoon Trough enters the tropical Atlantic through Sierra
Leone near 08N13W and continues to 07N18W. The ITCZ extends from
07N22W to 06N34W, then resumes west of a tropical wave to the
coast of Guyana. Outside the convection associated with the
tropical wave located near 18W/19W, scattered moderate convection
is from 07N-09N W of 50W. Gusty winds to 30 Kt are noted within
this area of convection.



Mosaic Doppler Radar from the SE U.S. shows numerous showers with
embedded tstms along the coast of Texas and the NW Gulf as well
as over eastern Texas and much of Louisiana. All this convective
activity is associated with a stationary frontal boundary and a
weak 1012 mb low pressure located over southern Texas. This front
will be the focus for heavy rain and local floodings from the
Texas Gulf coast to Alabama coast today. These weather conditions
are forecast to extend to the Florida Panhandle on Tuesday.
Again, areas of fog were observed over the NW Gulf under the
influence of a moist and warm SE wind flow. The remainder of the
Gulf is under the influence of a weak ridge, anchored by a 1022 mb
located over the western Atlantic. The pressure gradient between
the ridge and the frontal boundary is resulting in gentle to
moderate E-SE winds over the eastern Gulf and moderate to fresh
SE winds across the western Gulf, with higher gusts near the
tstms. The ridge is forecast to shift southward through early
Wednesday as the weak frontal boundary remains along the Northern
Gulf Coast while weakening. A late season cold front will enter
the NW Gulf early Wednesday followed by fresh northerly winds.


Convection has significantly diminished over the SW Caribbean and
now scattered moderate convection is mainly noted along the coast
of Nicaragua and NE Honduras. Similar convection is south of 10N
and east of 80W where the monsoon trough remains. Upper-level
diffluence is 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 basin. Please refer to the TROPICAL WAVE section above
for details. High pressure located over the western Atlantic near
29N66W combined with the Colombian/Panamanian low is supporting
fresh to locally strong trade winds over the south-central
Caribbean and the Gulf of Venezuela. These winds are expected to
expand across the eastern and central Caribbean on Wednesday as
pressure builds again north of the area. 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 over the
eastern Caribbean, including the Leeward Islands, Puerto Rico and
the Virgin Islands. Some of the islands continue to report haze
and dust, reducing somewhat the visibility.


Daytime heating, local sea breezes and mountain upslope lifting
will combine with available moisture to produce scattered
showers and isolated thunderstorms mainly during the afternoon
and early evening hours during the next two days. A tropical wave
moving across the island today and tonight could enhance the
shower activity.


High pressure prevails across most of the Atlantic Ocean. As
previously mentioned, a 1022 mb high is over the western Atlantic
near 29N66W while another high pressure center of 1023 mb is near
28N31W. In between, a surface trough remains and extends from
27N52W to 24N61W to 20N63W. Scatterometer data continue to support
the presence of this trough. Convection has diminished in
association with this feature since yesterday. This trough is a
reflection of an upper-level trough forecast to move eastward.
The high pressure over the western Atlantic will slide eastward
through mid-week as a cold front approaches from the west.

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