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AXNT20 KNHC 131751

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
151 PM EDT Fri Jul 13 2018

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.


…Gale Warning off the coast of Colombia in the Caribbean Sea…

The most recent scatterometer data provided observations of
minimal gale force NE-E winds across the south-central Caribbean,
particularly from 11N to 13N between 73W and 77W. In this area,
sea heights range from 11 to 15 feet based on an altimeter pass.
Minimal gale conditions are expected near the coast of Colombia at
night through Sun night. Please, see the High Seas Forecast,
under the AWIPS/WMO headers HSFAT2/FZNT02 KNHC, for more details.


Three tropical waves are between the west coast of Africa and the
Lesser Antilles. These waves were relocated this morning based on
visible satellite imagery, GOES-16 RGB Geocolor imagery, and
Model Diagnostics Guidance.

A tropical wave is added to the 1200 UTC analysis/surface map
along 16W/17W from 06N-13N. Scattered to numerous moderate to
isolated strong convection is just behind the wave’s axis from
10N-13N between 14W-17W. The Hovmoller Diagram clearly shows the
westward propagation of the wave. Model Diagnostics Guidance also
confirms the presence of this feature.

A tropical wave is along 41W from 08N-20N. Scattered moderate
convection is behind the wave’s axis and covers the area from 07N
to 13N between 34W and 41W. A recent scatterometer pass indicates
the wind shift associated with the wave’s axis. African dust
surrounds the wave.

A tropical wave is along 59W from 07N-19N. Scattered moderate
convection is noted near the base of the wave from 08N-12N between
58W-63W. This convective activity is affecting the islands of
Trinidad and Tobago as well as NE Venezuela. Light showers or
vicinity showers have been reported in Barbados, Trinidad and
Tobago. A good surge of moisture is related to the wave based on
the TPW product. Visible satellite imagery indicates some
inverted-V pattern in the cloud field associated with this system.
This wave will cross the Lesser Antilles through this evening,
and move across the eastern Caribbean tonight through Sun.

A tropical wave is along 70W from 09N-19N. This wave continue to
enhance some shower activity over western Venezuela. The TPW
animation indicates a modest surge of moisture associated with
this wave. However, the GFS computer model suggests an increase
in moisture in association with this wave as it moves across the
central Caribbean through Sat night, then across the western
Caribbean Sun and Sun night.

A tropical wave has its axis over SE Mexico and western Guatemala
and extends southward into the EPAC region. Currently, scattered
showers are near the wave’s axis. This system will move across the
Tehuantepec area this afternoon and evening.


The monsoon trough passes through the coastal sections of Senegal
near 14N17W to 11N30. The ITCZ extends from 11N30W to 12N40W to
07N50W to 09N58W. Aside from the convection related to the
tropical waves, scattered moderate convection is from 05N-09N
between 45W-53W.



A ridge continues to dominate the Gulf waters, with two weak high
pressure centers of 1021 mb located across the northern Gulf.
Under the influence of this system, mainly light to gentle
anticyclonic flow will prevail across much of the Gulf region
this upcoming weekend, with seas generally under 5 ft. Gentle to
moderate SE-S winds are expected across the western Gulf on the
western periphery on the ridge. According to the GOES-16 RGB
Geocolor imagery, African dust has reached the SE Gulf, including
the Yucatan Channel.

A surface trough will move westward off the Yucatan Peninsula
each evening through Tue. It will enhance nocturnal winds and
seas over the SW Gulf. Marine guidance suggests fresh to locally
strong NE-E winds and seas of 4-5 ft in association with this
thermal trough. A tropical wave will move westward across the Bay
of Campeche and the Tehuantepec region today.


Two tropical waves will continue to move across the basin. Refer
to the Tropical Waves section above for details.

A gale warning is in effect for the south-central Caribbean.
Refer to the Special Features section above for more information.

Saharan dust covers most of the Caribbean Sea, including the
Greater Antilles, where partly cloudy and hazy conditions prevail.

High pressure will build across the region behind each passing
tropical wave to freshen trade winds across the central Caribbean
waters. Winds will pulse to strong to near gale force each night
off the coast of Colombia through Tue, except to minimal gale
force tonight, Sat night and Sun night.


An area of low pressure, associated with the remnants of Beryl, is
located about 250 miles west-northwest of Bermuda. Although
upper-level winds are at best marginally conducive, this system has
become a little better organized today, and some additional
subtropical or tropical development is possible tonight and Saturday
while the low moves north-northeastward at about 10 mph. By Sunday,
the system should reach colder water north of the Gulf Stream, where
additional development is unlikely. The latest Tropical Weather
Outlook gives this system a low chance of tropical cyclone
formation during the next 48 hours. A weak low of 1014 mb is
analyzed on the 1200 UTC surface map near 33.2 69.6W. Visible
satellite imagery reveals that the low level center is totally
exposed due to the strong winds aloft.

A surface trough extends from the aforementioned weak low to
the NW Bahamas. The trough will move little through Sun night while
weakening. Scattered showers and isolated thunderstorms can be
expected along and southeast of the trough. A recent scatterometer
pass clearly indicates the wind shift associated with this trough.

The remainder of the Atlantic forecast area is under the influence
of the Bermuda-Azores High, with a center of 1034 mb located WNW
of the Azores near 39N38W. The ridge extends SW into the NE
Caribbean and the SE Bahamas. High pressure building westward
from the central Atlantic through Tue will support fresh to
strong trade winds south of 23N W of 65W. Winds will pulse to
strong north of Hispaniola at night this weekend.

The Saharan Air Layer (SAL) from CIMSS, and GOES-16 RGB Geocolor
imagery, depict a large area of African dust covering the tropical
Atlantic waters between the west coast of Africa and the Lesser

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