Tropical Weather Discussion
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AXNT20 KNHC 170605

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
104 AM EST Sat Feb 17 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 0000 UTC surface analysis and satellite imagery through
0545 UTC.


Caribbean Sea Gale Warning: A tight surface pressure gradient
between a high pressure system over the western Atlantic and
lower pressure over northern South America should continue to
support winds pulsing to minimal gale-force near the coast of
Colombia through Sun. The resultant waveheights with the gale
force winds are forecast to range from 10 to 14 feet. Please read
the latest NHC High Seas Forecast under AWIPS/WMO headers
MIAHSFAT2/FZNT02 KNHC for more details.


The monsoon trough axis enters the eastern Atlantic near 07N12W
and continues to 01N20W, where latest scatterometer data
indicates the ITCZ begins and dips to S of the Equator at 23W.
Scattered moderate isolated strong convection is within 120 nm S
of the axis between 20W-23W. Scattered moderate convection is
S of the axis within 30 nm of 02N14W, and also N of the axis
within 30 nm of line from 02N25W to 03N30W to 04N34W.



The western extension of Atlantic high pressure across the area
is maintaining pretty tranquil weather conditions throughout the
basin. At the surface, a 1022 mb high center is analyzed at
27N88W. In addition, satellite water vapor imagery depicts
abundant dry air in the mid and upper-levels of the atmosphere.
Surface observations and scatterometer data indicate that the
winds are light and generally southeast or southerly across much
of the area. Observed waveheights are in the 3 to 5 ft range
throughout, and little change is expected through Sun. A weak
surface trough extends from northern Florida southwestward to
over the far NE Gulf at 29N84W and to near 27.5N87W. Only
isolated showers are near this trough. Other isolated showers
are noted over some portions of the far SE waters of the gulf.
Areas of dense fog are expected over portions of the gulf mainly N
of about 27N during the morning hours producing sharply reduced
visibilities. Little change in the present synoptic pattern is
expected through Sun, however, winds and seas are forecast to
increase by early next week when high pressure strengthens over
the western Atlantic.


Please read the SPECIAL FEATURES section for details regarding
the Gale Warning near the coast of Colombia.

Only patches of clouds and embedded quick moving isolated showers
are seen across the Caribbean within patches of low-level
moisture. The trade winds in the area are fresh to strong, and
they are even stronger near the coast of Colombia as discussed
above. These winds are occurring due to the tight pressure
gradient between a 1025 mb high over the western Atlantic and the
typical lower pressures found over northern S America. No
significant changes are expected to occur today, however, winds
and seas will likely increase over the eastern and central
Caribbean on Sun and into early next week due to a tighter
pressure gradient attributed to stronger high pressure forecast to
build N of the area.


Tranquil conditions and fairly light winds are occurring across
the western Atlantic supported by a surface ridge and dry and
stable air aloft. Over the central Atlantic, an upper-level low
and accompanying surface trough is producing scattered showers and
isolated thunderstorms from 25N-28N between 42W-45W. Scattered
moderate convection, decreasing in coverage, is observed over the
deep tropics from 03N-09N between 43W-48W as this activity developed
from low-level convergence in that area. The activity is being
further aided aloft by a nearby upper jet stream branch. No
significant weather is occurring over the eastern Atlantic as
atmospheric conditions are rather stable. Isolated to scattered
showers moving quickly westward are present S of 25N W of 59W.
This activity is affecting the Lesser Antilles, Puerto Rico
and immediate surrounding islands. A steady stream of mid and
upper level moisture in the form of broken mid and upper level
clouds is seen streaming northeastward from northeastern S America
to within 220 nm either side of line from 05N50W to 11N37W to
14N26W and to inland the African coast at 17N16W. Isolated showers
are possible elsewhere from 02N-10N between 40W and the coast of
S America, and also from 10N-18N between 20W-35W.

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