Tropical Weather Discussion
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AXNT20 KNHC 192336

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
736 PM EDT Sat Aug 19 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 1800 UTC surface analysis and satellite imagery through
2315 UTC.

Harvey is downgraded to a tropical depression at 19/2100 UTC. At
this time, the center of Harvey is near 14.1N 70.0W or about 120
nm NNW of Curacao, and about 770 nm E of Cabo Gracias a Dios on
the Nicaragua/Honduras border moving W or 275 degrees at 19 kt.
Estimated minimum central pressure is 1007 mb. Maximum sustained
wind speed is 30 kt with gusts to 40 kt. Some slow strengthening
is possible during the next couple of days, and Harvey could
regain tropical storm status Sunday or Sunday night. Satellite
imagery indicates that the strong convection associated with
Harvey remains west of the center, and covers the area from 12N-
16N between 69-72W. Interests in the central and western Caribbean
Sea, northern Nicaragua, northern Honduras, Belize, and the
Yucatan Peninsula of Mexico should monitor the progress of Harvey.
See the latest NHC Forecast/Advisory under AWIPS/WMO headers
MIATCMAT4/WTNT24 KNHC for more details.

A tropical wave extends from 21N43W to 10N44 moving W at 15-20
kt. Satellite imagery indicates a large area of cloudiness but
convection is limited in association with this wave. Saharan dust
surrounds the wave. This system coincides with a well defined 700
mb trough, and a high amplitud northward bulge of moisture is
noted on the TPW product. The wave is embedded in a dry air mass,
and upper-level winds are expected to become too strong to support
development in a couple of days. Therefore, tropical cyclone
formation is not likely while this system moves northwestward at
about 13 kt.

A tropical wave is over the western Caribbean and extends from
western Cuba, along 81W/82W to near 10N82W moving W at 10-15 kt.
The wave shows up very well on the TPW animation and 700 mb
streamline analysis. Energy from the wave has fractured to the
N-NE and is analyzed as a surface trough between the NW Bahamas
and the Florida peninsula. The trough extends from 23N79W to
28N77W. Currently, the wave is helping to induce showers and
thunderstorms over central Cuba, and near the Cayman Islands.
Showers and thunderstorms are also noted ahead of the wave axis
over eastern Honduras and eastern Nicaragua.

The monsoon trough extends from the African coast near 12N16W to
09N20W to 10N29W. The Intertropical Convergence Zone axis extends
from 10N47W to 09N61W. Scattered moderate convection is from 08N-
10N between 27W-31W, and from 09N-12N between 51W-55W.


A large and well defined upper-level low centered over the SE
Gulf near 24N85W continues to generate scattered showers and
thunderstorms, particularly between 85W-90W, including the
northern Yucatan peninsula. A surface trough, reflection of this
upper-level low is analyzed on the 2100 UTC surface map from
30N83W to 24N86W. A scatterometer pass showed very well the wind
shift associated with this trough. The western half of the Gulf is
under the influence of a ridge, anchored by a 1017 mb high
pressure centered near 28N94W. Isolated showers and light to
gentle anticyclonic winds prevail W of 90W. The upper-low will
drift westward reaching the central Gulf on Monday. This system
will continue to enhance the development of showers and tstms
across the Gulf waters on Sunday.

The primary area of concern across the Caribbean Sea is Tropical
Cyclone Harvey, forecast to move across the central and western
Caribbean through Monday. Please, see Special Features section
for more details. A tropical wave is along 81W/82W. Please, see
the Tropical Waves section for details. Moisture associated with
this tropical wave will continue to affect the northern central
America and NW Caribbean, including also western Cuba, increasing
the likelihood of showers and thunderstorms on Sunday.

Daytime heating, local sea breezes, and mountain upslope lifting
will combine with available moisture to produce scattered showers
and thunderstorms across the island mainly during the afternoon
and evening hours through the weekend.

As previously mentioned, the northern part of the tropical wave
currently moving acrosss the western Caribbean is analyzed as a
trough between the NW Bahamas and the Florida peninsula. This
trough is generating scattered showers and tstms, and will
continue to move westward across south Florida and the Straits of
Florida tonight and Sunday accompanied by active weather. Showers
and thunderstorms are forecast to increase across south Florida
tonight, and continue on Sunday, with possible locally heavy
rain. Another trough is analyzed NE of the Leeward Islands and
extends from 24N59W to near Barbuda. This trough continues to
produce disorganized showers and thunderstorms mainly from 19N-23N
between 58W-63W. Environmental conditions are not expected to be
conducive for development of this system during the next couple of
days while it moves west-northwestward at 15 to 20 kt. Conditions
could become slightly more conducive for development once the
system is near the northern Bahamas or Florida around the middle
of next week. An area of fresh to strong winds is noted per
scatterometer data on the northern side of this trough from 19N-
24N between 57W-63W. The remainder of the Atlantic is under the
influence of a ridge, with a center of 1023 mb located near
32N40W. Fresh to strong Northerly winds are aslo noted between the
coast of Africa and the Madeira/Canary Islands. These winds are
the result of the pression gradient between the Atlantic ridge and
lower pressures over west Africa.

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