Tropical Weather Discussion
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AXNT20 KNHC 182349

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
748 PM EDT Fri Aug 18 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.


Tropical Storm Harvey is located near 13.4N 62.9W at 18/2100 UTC,
or about 115 nm WSW of St. Lucia, moving west or 275 degrees at
18 kt. Estimated minimum central pressure is 1005 mb. Maximum
sustained wind speed is 35 kt with gusts to 45 kt. The low-level
center of Harvey remains near the eastern edge of a strong, but
poorly organized, convective area that covers the area from 11N-
15N between 62W-66W. Harvey will move through the eastern Caribbean
Sea tonight and through the central Caribbean Sea Saturday and
Saturday night. Interests in the Caribbean Sea and the adjacent
land areas of eastern Central American and northern South America
should monitor the progress of Harvey. Locally heavy rains could
occur tonight over portions of the Windward Islands and the
offshore islands of northern Venezuela. Locally heavy rains could
also occur over Aruba, Bonaire, and Curacao on Saturday. See the
latest NHC Intermediate Public Advisory under AWIPS/WMO headers
MIATCPAT4/WTNT34 KNHC, and the full Forecast/Advisory under
AWIPS/WMO headers MIATCMAT4/WTNT24 KNHC for more details.

Shower and thunderstorm activity associated with an area of low
pressure located near 18N52W or about 435 nm east-northeast of
the Leeward Islands have become less organized since yesterday due
to strong upper-level winds, and satellite data suggest that the
surface circulation has become less defined. This low pressure
area is along a tropical wave than extends from 21N52W to 10N52W.
A cluster of strong convection is seen north of the low center
and covers the waters from 18N-20N between 51W-53W. Scattered
moderate convection is noted elsewhere from 16N-21N between 49W-
54W. Environmental conditions are expected to be only marginally
conducive for development during the next couple of days while
this system moves west-northwestward at about 20 mph, and the
chances for tropical cyclone formation appear to be decreasing.


A tropical wave is in the E Atlantic with axis extending from
20N35W to a 1010 mb low pressure located near 14N36W to 10N36W.
Satellite imagery indicates a large cyclonic circulation in the
cloud field, but convection is limited in association with this
low. Saharan dust surrounds the wave/low. This system coincides
with a well defined 700 mb trough, and a high amplitud northward
bulge of moisture is noted on the TPW product. Environmental
conditions appear somewhat conducive for gradual development over
the next few days while the system moves west-northwestward to
northwestward at about 18 kt, but upper-level winds are forecast
to become unfavorable by the middle of next week. This system has
a low change of becoming a tropical cyclone within the next 48

A tropical wave extends from the central Bahamas across eastern
Cuba and Jamaica to the SW Caribbean near 10N78W moving W at
15-20 kt. A cluster of moderate to isolated strong convection is
along the wave axis between the coast of eastern Cuba and Jamaica.
Isolated moderate convection is over the central Bahamas and
regional waters. The wave shows up very well on the TPW animation
and 700 mb streamline analysis. Moisture associated with this wave
will spread across the NW Bahamas and central Cuba by Saturday
morning, and across south Florida and western Cuba by Saturday
afternoon and evening, increasing the likelihood of showers and
thunderstorms, with the potential of locally heavy rain and
localized flooding.

The tropical wave previously located over the Bay of Campeche
is now over Mexico generating some convective activity over the
State of Veracruz. For further information about this tropical
wave see the Tropical Weather Discussion for the eastern Pacific


The monsoon trough extends from the African coast near 13N17W to
12.5N20W to 13N30W to 11N35W to 10N46W. Besides the convection
mentioned in the tropical wave and special features sections,
scattered moderate convection is from 09N to 12.5N between 20W-
23W. Similar convection is noted within 90 nm S of trough between
37W-41W, and near 12N45W.


A weak ridge continues to dominate the Gulf waters. A pair of
1017 mb high centers are noted along the ridge axis, one near the
Florida Big Bend and the second one over the NW Gulf. Mainly light
to gentle winds are observed under the influence of the ridge. As
of 2100 UTC, a surface trough is analyzed from 31N85W to 27N87W.
Scatterometer and surface data indicate the wind shift associated
with this trough. A thermal trough will develop during the
evening hours over the Yucatan Peninsula before pushing offshore
into the SW Gulf each night. A surge of fresh winds will accompany
this trough. Little change in this weather pattern is expected
through early next week. In the upper levels, a large and well-
defined upper-level low is spinning over the Florida Keys and
western Cuba. This system is helping to induce some shower and
thunderstorm activity over the eastern Gulf and the Florida
Peninsula. The upper-low will drift westward across the eastern
Gulf during the weekend.


A tropical wave is over eastern Cuba along 77W/78W. Please, see
the Tropical Waves section for details. Tropical Storm Harvey
will move through the eastern Caribbean Sea tonight and through
the central Caribbean Sea Saturday and Saturday night. Please,
see Special Features section for more details. An upper-level low
spinning over western Cuba supports scattered showers and tstms.
Scattered showers and tstms are also noted over the SW Caribbean,
likely associated with the eastern extent of the Pacific monsoon
trough combined with a diffluent pattern aloft.

Daytime heating, local sea breezes and mountain upslope lifting
will combined with available moisture to produce isolated to
scattered showers and thunderstorms mainly during the afternnon
and evening hours.

A pair of tropical waves are moving westward across the tropical
Atlantic. The northern portion of a tropical wave is affecting
the central Bahamas. Please, see Special Features and Tropical
Wave sections above for details. The remainder of the Atlantic is
under the influence of a ridge, with a center of 1024 mb located
near 32N38W. A belt of fresh to locally strong NE-E winds is
noted per scatterometer data roughly between 17N-23N due to the
pressure gradient between the ridge and the tropical waves and
associated lows located between the coast of Africa and the
Lesser Antilles. 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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