[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 201741
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
141 PM EDT Thu Sep 20 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 1200 UTC surface analysis and satellite imagery through
1715 UTC.

...TROPICAL WAVES...

An eastern Atlantic tropical wave is located along 25W from 05N-
20N moving west at 10 to 15 kt. The total precipitable water (TPW)
satellite animation shows a well-depicted plume of moisture
trailing the wave between 22W and the coast of Africa. Scattered
showers are near the wave axis south of 12N.

A central Caribbean tropical wave has its axis along 70W extending
from the Dominican Republic to western Venezuela moving west
around 15 kt. TPW imagery shows enhanced moisture associated with
this tropical wave. Scattered moderate convection is noted from
15N-19N between 67W-72W. This activity is currently affecting the
southern coast of the Dominican Republic. Satellite imagery
indicates some Saharan dust east of the wave from 12N-24N between
57W-67W. Puerto Rico and the Virgin Islands are reporting hazy
conditions. Strong wind gusts are possible near showers and
storms associated with this wave through Friday as it moves
westward through the central Caribbean. The wave is expected to
increase the likelihood of showers and thunderstorms over the
remainder of Hispaniola today, and across eastern Cuba and Jamaica
on Friday.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends from coastal sections of Sierra
Leone near 08N13W to 07N16W to 09N23W. The ITCZ begins near
09N26W and extends to 07N35W to 09N46W, then resumes from 09N52W
to the Guyana/Venezuela border. Scattered moderate and isolated
strong convection is seen within 270 nm south of the trough axis
between 21W and the coast of Africa. Scattered moderate convection
is noted with the ITCZ from 07N-10N between 50W and the coast of
South America.

...DISCUSSION...

GULF OF MEXICO...

Water vapor imagery and model analyses indicate the presence of
an upper-level cyclonic shear axis stretching from the Florida
Straits to southeast Louisiana. At the surface, a trough extends
from near Ft. Myers, FL southwestward to near 24N86W. Another
trough extends through the central Bay of Campeche from 24N91W to
the coast of Mexico near 18N93W. Isolated showers and thunderstorms
are noted over the Bay of Campeche. This trough and associated
moisture will move westward, reaching mainland Mexico by late Fri.
A small 1019 mb surface high is centered over northern Florida
near 30N83W. Ridging will build in across the northern Gulf,
producing gentle to moderate east to southeast winds and 2 to 4 ft
seas across the basin through Sun.

CARIBBEAN SEA...

A tropical wave is moving across the east-central Caribbean Sea.
See the Tropical Waves section for more details.

A 1008 mb low along the monsoon trough is located in the southwest
Caribbean near 11N82W. These features are producing numerous
moderate to strong convection over the southwest Caribbean from
10N-13N between 77W-86W. This activity is affecting parts of
northern Costa Rica and Nicaragua, including the city of
Bluefields, where heavy thunderstorms are currently being
reported. Plenty of moisture will persist over the southwest
Caribbean through Saturday as the tropical wave, currently along
70W, reaches the area and moves inland into central America late
Sat or early Sun.

Recent scatterometer data show fresh to occasionally strong trade
winds south of 18N, between 70W-83W, while an altimeter pass
indicates seas as high as 11 ft near the coast of Colombia. Over
the eastern Caribbean, winds are in the 15-20 kt range with seas
near 8 ft. High pressure building from the central Atlantic into
the central Bahamas will continue to support similar winds and
seas, especially over the south-central Caribbean, through Friday
night.

Scattered showers and thunderstorms embedded in the trade wind
flow are moving across Trinidad and Tobago into far NE Venezuela.

ATLANTIC OCEAN...

A 1012 mb surface low, formerly a tropical wave, is producing a
concentrated area of thunderstorms near 10.5N49W, or about 740 nm
east of the Windward Islands. Although this disturbance shows
some signs of organization on satellite imagery, there is no
evidence of a surface circulation at this time. A recent ASCAT
pass confirms the presence of an open trough. Scattered moderate
convection in a banding pattern is noted from 10N-13N between 46W-
50W. Some additional development is possible today before upper-
level winds become highly unfavorable for tropical cyclone
formation starting tonight and continuing through the weekend.

The remnant of Joyce is analyzed as a 1014 mb low near 30N32W. A
trough extends from the low to 26N34W. No significant convection
is noted.

A cold front enters the forecast area near 31N69W and continues
southwestward to 29N73W to 29N79W. Scattered showers are within
120 nm ahead of the frontal boundary between 70W-78W. East of the
front, a surface trough is analyzed from 29N62W to 23N70W.
Scattered showers and thunderstorms are located within 150 nm east
of the trough. Scatterometer data indicate winds of 20-25 kt are
currently occurring north of 29N between 64W-69W. This area of
20-25 kt winds will move eastward over the area for the next 12
hours before gradually weakening. The aforementioned front will
sink SE to the waters north of 27N through Fri before the front
dissipates.

A relatively weak pressure gradient prevails over the remainder
of the Atlantic area.

For additional information please visit
http://www.hurricanes.gov/marine

$$
HAGEN/GR
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