[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 271150
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
750 AM EDT Mon Aug 27 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
1145 UTC.

...TROPICAL WAVES...

A far eastern Atlantic tropical is just west of the African coast
with its axis along 20W from 04N to 20N, moving westward at 10
kt. The wave is embedded within the broad monsoonal trough region
of W Africa. Moisture and convection within this region of the far
eastern Atlantic has increased during the past few days as
observed on GOES-16 imagery. The latest satellite imagery shows
scattered moderate to strong convection just east of the wave axis
to along and just inland the coast of Africa from 07N to 12N.
This activity is holding together as it moves away from the
African coast. Similar convection is west of the wave axis along
and within 120 nm south of the monsoon trough between the wave and
23W.

A central Atlantic tropical wave has its axis along 50W from 04N
to 20N, moving westward at 10-15 kt. This wave is surrounded by a
rather stable and dry environment. Only isolated showers are seen
within 150 nm west and within 120 nm east of the wave axis from
08N to 14N.

A tropical wave that was tracked across the central Atlantic
during the past few days appears to have become more defined at
the surface and low-levels near 60W, moving west at 10-15 kt. The
700 mb model wind and streamline fields support a tropical wave
in this general area. Scatterometer data from last night
highlighted some evidence of a northeast to southeast shift in
wind direction across the wave axis. Scattered showers are within
60 nm east of the wave axis from 14N to 20N.

A western Caribbean Sea tropical wave has its axis along 81W
south of 20N, moving westward at about 15 kt. The upper-level
flow is cyclonic north of 14N in association with an upper-level
low over central Cuba. The northern portion of the wave, being
the case that it is in the favorable location east of the upper-
level low, is helping to trigger off scattered showers within 120
nm west of the wave axis from 18N to 20N. Scattered moderate
convection prevails south of 13N affecting Central America and
adjacent waters between 79W-84W.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis passes through the coastal sections of
Guinea-Bissau near 12N16W to 09N25W to 12N38W and to just east of
the tropical wave along 48W/49W. ITCZ from 6N50W to 05N53W. Aside
from convective activity associated with the far eastern Atlantic
tropical wave, scattered moderate isolated strong convection is
within 75 nm on either side of the monsoon trough between 23W and
30W.

...DISCUSSION...

GULF OF MEXICO...

An upper-level trough extends from northeastern Florida to
29N83W, and continues as a shear axis to an upper-level low at
24N93W. At the surface, a westward moving trough extends from
2991W to 23N92W. Upper-level cyclonic wind flow covers nearly the
entire Gulf of Mexico east of 94W eastward. A second upper-level
low is noted at the coast of Mexico near 20N97W. With these
features in play along with a very moist and unstable atmosphere
in place, scattered shower and thunderstorm activity will continue
over much of the basin through the next couple of days.

A surface trough will develop during the evening hours in the
Yucatan Peninsula, before pushing offshore into the SW corner of
the Gulf of Mexico each night. This trough, in combination with
Sunday's daytime heating acting on ample instability in place,
triggered off scattered moderate isolated strong convection over
much of the Yucatan Peninsula. Over the past few hours this
activity has diminish some as it pushes off the west coast of the
Yucatan and to the eastern Bay of Campeche. Scattered showers and
isolated showers remain over sections of the Yucatan Peninsula.
A surge of moderate to fresh northeast to east winds will
accompany this trough. A weak surface ridge will remain over the
rest of basin, with its associated gradient supporting a mainly
gentle to moderate wind flow regime.

CARIBBEAN SEA...

An upper-level trough extends from a small upper-level low near
22N63W west-southwestward to Hispaniola, and continues to another
upper-level low over east-central Cuba. A trough extends from
this low southward to just south of Jamaica and to northwestern
Colombia. Plenty of atmospheric instability over the western half
of the Caribbean for these features to work with is bringing
scattered moderate convection in clusters over the waters just
south of Cuba to 19N between 81W and 85W. Isolated moderate
convection is seen elsewhere north of 13N west of 77W. Instability
from the upper-level low over Cuba earlier resulted in scattered
to numerous showers and thunderstorms over much of the central and
eastern sections of that island. This activity has decreased
during the past few hours, but is expected to quickly re-develop
today as daytime gets underway. The activity will gradually shift
from east to west as the upper low tracks further away to the
W.

The eastern segment of the eastern Pacific monsoon trough
stretches eastward into the far southwestern Caribbean to the
northwestern coast of Colombia. Scattered showers and thunderstorms
are south of 13N and west of 75W.

Fresh to strong winds, and building seas to 10 feet, will continue
in the south central Caribbean Sea through Wed. A tropical wave
will approach the waters east of the Lesser Antilles on Tue
accompanied by fresh easterly winds and wave heights expected
to max out around 8 ft. The wave will enter the eastern Caribbean
early on Wed, increasing the likelihood of scattered showers and
isolated thunderstorms over much of the Lesser Antilles.

ATLANTIC OCEAN...

Several small surface and upper-level feature are evident across
this area of the discussion domain.

The tail-end of an upper-level trough extends from within 180 nm
offshore the southeastern United States southwestward to NE
Florida. An upper-level low moving westward is near 28N71W, with
and inverted trough stretching southwestward to 25N74W and to an
upper-level low over central Cuba. Another inverted trough
extends from the upper low northeastward to north of the area at
32N70W. At the surface, a trough with good track history, is
analyzed from near 29N75W to the central Bahamas and to just north
of the coast of Cuba at 22N78W. Latest satellite imagery shows
scattered showers and thunderstorms moving westward over much of
the central Bahamas west through the Straits of Florida and to
southern Florida. The surface trough is forecast to move across
the area through Mon. Gentle to moderate winds will be associated
with this trough. A small upper-level low moving steadily westward
is seen in water vapor imagery to be near 22N63W, with a trough
extending westward to Hispaniola and to an upper-level low over
east-central Cuba. This upper low is showing a surface signature
identifies as a trough from 27N64W to near 22N66W. Scattered
moderate convection is noted within 180 nm west of the trough from
24N to 27N. Isolated showers and thunderstorms are elsewhere to
the west of 60W.

An upper-level trough stretches from an upper-level low also
located well north of the area at 35N39W southwestward through
32N45W to 27.5N50W and to the upper-level low that is near 22N63W.
A pair of surface troughs are analyzed from near 32N43W to 29N50W,
and from near 32N50W to 29N56W to 31N51W. Scattered moderate
convection is within 75 nm southeast of the first trough. Isolated
showers and weak thunderstorms are along and within 30 to 60 nm
of the second trough. Isolated showers are elsewhere to the
north of 24N between 45W and 60W.

Outside the above described features, surface high pressure is
present across the Atlantic, with the strongest high pressure
found north of 28N and east of 50W.

Water vapor imagery and the Total Precipitable Water (TPW)
animation reveal that atmospheric moisture is increasing over
much of the basin east of 52W.

East winds will pulse to fresh to strong at night just north of
Hispaniola through Tue. A weak surface ridge will remain over the
remainder of these waters, with its associated gradient supporting
gentle to moderate east to southeast winds west of about 50W.

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

$$
Aguirre/ERA
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