Tropical Weather Discussion
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AXNT20 KNHC 200528

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
128 AM EDT Sun Aug 20 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 0000 UTC surface analysis and satellite imagery through
0515 UTC.


A tropical wave extends its axis from 20N45W to 10N46W, moving
west at 15-20 kt. Satellite imagery indicates a large area of
cloudiness but convection is limited in association with this
wave due to Saharan dust intrusion. This system coincides with a
well defined 700 mb trough, and a high amplitude northward bulge
of moisture is noted on the TPW product.

T.S. Harvey has been degraded to an open tropical wave with axis
extending from 19N70W to a 1007 mb surface low near 14N71W to
11N71W. An Air Force Reserve Hurricane Hunter aircraft investigated
Harvey earlier this evening and was unable to close off a center
of circulation. Maximum surface winds, as measured by the plane,
remain near 30 kt around the wave`s axis. A fast westward motion
is expected to continue with this system for the next couple of
days as the wave moves along the southern periphery of the
subtropical ridge.

A tropical wave is over the western Caribbean with axis extending
from western Cuba along 83W to near 10N83W, moving west 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
northeast and is analyzed as a surface trough between the northern
Bahamas and the Florida peninsula, from 28N79W to 24N80W. Currently,
the wave is enhancing showers and thunderstorms over west Cuba
and near the Cayman Islands. Showers and thunderstorms are also
noted ahead of the wave`s axis affecting portions of Honduras and
adjacent waters.


The monsoon trough extends from the African coast near 14N17W to
10N36W. The Intertropical Convergence Zone extends from 11N48W to
09N61W. Scattered moderate convection is observed within 100 nm on
either side of the monsoon trough.



A large and well defined upper-level low centered over the
southeast Gulf near 25N85W continues to generate scattered
showers particularly between 88W-92W and the Florida Straits area.
A surface trough, reflection of this upper-level low, is analyzed
from 30N84W to 26N85W. 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 surface ridge, anchored by a
1016 mb high pressure centered near 29N93W. Isolated showers and
light to gentle anticyclonic winds prevail west of 90W. The
upper-low will drift westward reaching the central Gulf by
Monday. This system will continue to enhance showers and
thunderstorms across the Gulf waters on Sunday.


Two tropical waves are moving across the basin. Refer to the
section above for details. Moisture associated with these
tropical waves will continue to affect the central Caribbean,
central America and northwest Caribbean increasing the likelihood
of showers and thunderstorms today.


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 across the western Caribbean is analyzed as a
trough between the northwest Bahamas and the Florida peninsula.
This trough is generating scattered showers and thunderstorms west
of 76W, 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 surface trough is analyzed northeast
of the Leeward Islands extending from 24N62W to 20N63W. This
trough continues to produce disorganized showers and thunderstorms
from 17N-21N between 60W-65W. 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 surface ridge, anchored by a
1024 mb high centered near 33N39W. Fresh to strong northerly winds
are also noted between the coast of Africa and the Madeira/Canary
Islands. These winds are the result of the pressure gradient
between the Atlantic ridge and lower pressures over west Africa.

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