[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 221157
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
757 AM EDT Sat Sep 22 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 0600 UTC surface analysis and satellite imagery through
1115 UTC.

...Special Features...

Tropical Depression Eleven is centered near 13.0N 53.5W at
22/0900 UTC, or 440 nm (810 km) E of the Windward Islands, moving
W at 4 kt. A slow westward or west-northwestward motion is
expected during the next couple of days. Estimated minimum central
pressure is 1007 mb. Maximum sustained wind speed is 30 kt with
gusts to 40 kt. Little change in strength is forecast during the
next day or so, and the depression is expected to dissipate east
of the Lesser Antilles by Sunday night. Scattered moderate
convection is between 60 nm-180 nm in the E semicircle of the low
center. See latest NHC forecast/advisory under AWIPS/WMO headers
MIATCMAT1/WTNT21 KNHC for more details.

Shower and thunderstorm activity continues to become better
organized near the center of a low pressure system located about
435 nm south of the southern Cabo Verde Islands, and a tropical
depression appears to be forming. If these trends continue,
advisories will be initiated on this system later today while the
low moves westward at about 15-20 kt. Scattered moderate
convection is observed within about 120 nm W semicircle of the
low center located near 07.5N22W. Similar convection is noted
elsewhere from 06N-09N between 18W-20W, and from 08N-11N between
23W-25W. The system now has a high chance of tropical cyclone
formation within the next 48 hours. Please refer to the latest
Tropical Weather Outlook under AWIPS/WMO headers MIATWOAT/ABNT20
KNHC for more information.

Satellite imagery indicates that a non-tropical low pressure system
is forming along a frontal boundary about 785 nm west-southwest of
the Azores. Conditions are expected to become conducive for the
low to acquire subtropical or tropical characteristics, and a
subtropical or tropical cyclone is likely to form by early next
week while the low meanders over the central Atlantic Ocean. The
system now has a medium chance of tropical cyclone formation
within the next 48 hours. Please refer to the latest Tropical
Weather Outlook under AWIPS/WMO headers MIATWOAT/ABNT20 KNHC for
more information.

...TROPICAL WAVES...

The tropical wave has its axis along 39W/40W from 04N-16N and is
moving west at 10-15 kt. The wave corresponds nicely with a
maximum in TPW imagery. Model analyses depict an associated 700 mb
trough along 39W. Isolated showers are near the wave axis.
Little change is expected with this wave over the next 24-48
hours.

A western Caribbean Sea tropical wave has its axis along 83W,
moving west at 10-15 kt. This wave is well depicted in model
guidance, and TPW imagery shows abundant moisture in its
environment. Numerous moderate and isolated strong convection is
noted from 14N-17N between 81W-86W. Similar convection is also
seen over the SW Caribbean, where the wave meets the monsoon
trough. Moisture associated with this wave will spread across
Central America today and tonight, increasing the likelihood of
showers and tstms.

...MONSOON TROUGH/ITCZ...

The monsoon trough extends across Africa along 17N. The trough
begins over the Atlantic near 07N22W to 07N37W. The ITCZ begins
near 07N41W to 10N52W. Scattered moderate convection is within
about 150 nm NE of the ITCZ axis.

...DISCUSSION...

GULF OF MEXICO...

An upper-level cyclonic circulation centered near 27N85W is
enhancing convection across the eastern half of the basin mainly
east of 90W. A surface trough is analyzed over the SE Gulf along
84W from 23N-26N. Surface ridging prevails across the remainder
of the basin. The ridge will support gentle to moderate easterly
winds and seas 3 ft or less across most of the Gulf of Mexico
through the middle of next week. A surface trough will develop
over the Yucatan peninsula each evening, shift W over the SW Gulf
each night, then dissipate by morning. Moderate to fresh winds
will accompany the trough.

CARIBBEAN SEA...

A tropical wave is moving across the western Caribbean. Please
see the Tropical Waves section for more details.

The eastern Pacific monsoon trough combined with diffluence aloft
is helping to induce scattered showers over portions of Costa
Rica and Panama. Plenty of moisture will persist over the
southwest Caribbean today. Otherwise, fresh to strong
winds prevail over the south-central Caribbean. These winds will
diminish across most of the basin by Sun night.

ATLANTIC OCEAN...

Currently, there are two tropical waves and a tropical depression
between the west coast of Africa and the Lesser Antilles. Please
see the Special Features/Tropical Waves sections for more details.

A weakening front extends from a 1010 mb low pressure centered S
of Bermuda near 29.5N64.5W to 28N68W. The front will dissipate by
midday today, while the low slowly drifts W across the northern
forecast waters through early next week. This low is producing
only minimal shower activity. Strong upper-level winds are
expected to diminish by Sunday or Monday, which could allow for
some slow development of this system while it moves westward and
then northwestward over the southwestern Atlantic Ocean. By the
middle of next week, upper-level winds are likely to strengthen
again, which would limit additional development as the system
moves closer to the southeastern coast of the United States.

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

$$
GR/Hagen
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