Tropical Weather Discussion
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AXNT20 KNHC 211756

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
156 PM EDT Fri Apr 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
1645 UTC.


The center of Post-Tropical Cyclone Arlene at 1500 UTC was
near 39.3N 49.9W and is moving southwest at 20 knots. The
estimated minimum central pressure is 995 mb. The maximum
sustained wind speed is 45 knots with gusts to 55 knots. Isolated
moderate convection is within 120 nm of the center. Please refer
to the public advisory under the WMO header WTNT31 KNHC and under
the AWIPS header MIATCPAT1 for more details.

A tight pressure gradient generated between a broad low pressure
system centered south of Post-Tropical Cyclone Arlene and an area
of high pressure to the west is supporting gale-force winds north
of 30N between 47.5W and 52W. Seas in this area will range
between 12 to 17 ft through the gale event. These conditions will
continue through tonight. Please see the latest High Seas Forecast
product under the WMO header FZNT02 KNHC and under the AWIPS
header MIAHSFAT2 for further details.


The Monsoon Trough extends across the western Africa coast from
09N13W to 03N18W. The Intertropical Convergence Zone continues
from 03N18W to 00N24W to the coast of Brazil near 02S44W.
Scattered moderate convection prevails south of 04N between 16W
and 39W and south of 07N east of 16W.



High pressure extends across the northern Gulf coast supporting
moderate southeast winds over the northern Gulf, and moderate
easterly winds over the southern Gulf. The combination of an
upper trough and a surface trough extending from 25N84W southward
across the Yucatan Channel supports numerous showers and scattered
thunderstorms south of 26N and east of 89W. A thermal trough over
the southwestern Gulf has dissipated. Over the next 24 hours a
broad area of low pressure may develop over the southeastern Gulf
as moisture spreads north and east across southern Florida.


A surface trough extends from the southeastern Gulf to the
Yucatan Channel near 21N86W to 17N86W. The combination of this
surface trough and an upper level trough over the area supports
scattered showers and thunderstorms north of a line from 21N87W to
14N75W. Generally light to gentle winds are within 180 nm of the
surface trough axis. High pressure north of the eastern Caribbean
supports mainly moderate trade winds over the remainder of the
Caribbean, except light winds over the southwestern Caribbean.
Over the next 24 hours the showers and thunderstorms over the
northwestern Caribbean will gradually shift north and east as a
broad area of low pressure develops over the Gulf of Mexico, and
the upper trough lifts northeast. Little change is expected


Increasing moisture from an upper trough to the west of the area
is supporting showers and isolated thunderstorms across western
Haiti. Expect the moisture to spread across the remainder of
Hispaniola through Saturday with showers and thunderstorms likely
across the island Saturday and Sunday.


Post-Tropical Cyclone Arlene is over central Atlantic waters
north of the area. Gale- force winds are south of a 990 mb
surface low located south of Arlene. See the Special Features
section above for further details. A surface ridge extends across
the western Atlantic anchored by a 1021 mb high centered near
30N69W. Showers are beginning to spread across the waters
southeast of the Bahamas to the east of an upper trough. An old
frontal trough extends from 22N64W to 25N74W. No convection is
associated with this boundaries at this time. To the east, a cold
front enters the area from 31N39W to 23N50W. Isolated moderate
convection is within 300 nm east of the front north of 26N. High
pressure of 1019 mb centered near 28N22W dominates the remainder
of the eastern Atlantic. Over the next 24 hours showers and
thunderstorms will increase across the Bahamas. The gale force
winds will end Saturday morning.

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