[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 222353
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
753 PM EDT Wed Aug 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 1800 UTC surface analysis and satellite imagery through
2345 UTC.

...TROPICAL WAVES...

A far eastern Atlantic tropical wave has its axis along 27W from
07N-20N, moving westward at 10-15 kt. The wave is embedded within
a very dry and stable environment inhibiting convection at this
time. Only isolated weak showers and thunderstorms are seen within
120-180 nm east of the wave from 10N to 11N.

A central Atlantic tropical wave has its axis extending along 46W
from 05N-19N, moving westward at about 10 kt. This wave is also
embedded within a very dry and stable environment caused by
Saharan Air Layer outbreak of the past several days that is
spreading westward across the central and eastern Atlantic.
Scattered moderate convection is within 120 nm east of the wave
from 08N to 10N. Isolated showers are south of 10N, where the wave
meets the monsoon trough.

An eastern Caribbean Sea tropical wave has its axis along 68W
south of 19N to well inland Venezuela. It is moving westward near
15-20 kt. Scattered showers are increasing south of 10N over
Venezuela.

A west Caribbean tropical wave has its axis along 80W from 07N to
20N, moving westward near 15 kt. Previous deep convection with
this wave has dissipated. Scattered moderate convection prevails
south of 12N between 80W-84W.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends from the African coast near
12N17W to 09N44W. The ITCZ axis begins at 09N44W and continues to
10N55W. Scattered moderate convection is within 120 nm of the
ITCZ.

...DISCUSSION...

GULF OF MEXICO...

High pressure of 1021 mb is analyzed near 26N95W, while a surface
trough extends from southeastern Georgia southwestward to the
northeastern gulf and continues to near 27N91W. The nocturnal
Yucatan Peninsula trough has moved across the southwestern gulf
during the late night and early morning hours, and is analyzed
from near 21N96W to 18N94W. The present pressure gradient across
the gulf generally supports light to gentle winds throughout,
except for gentle to moderate winds south of 26N and relatively
low seas of 1 to 3 ft. Scattered showers and thunderstorms are
observed over the far southwest section of the gulf south of 21N
and west of 94W in association with the nocturnal trough that
moved offshore the Yucatan Peninsula during the overnight hours.
Other scattered showers and thunderstorm activity continues to
increase over the north-central gulf in association with the
aforementioned surface trough, with further support from an upper-
level trough that is dropping southward across the norther gulf
section. The activity over the far southwest is expected to weaken
during the afternoon. It should then re-develop tonight and Thu
night as the surface trough again moves across those same waters.
The activity over the north- central gulf should continue to
increase through this afternoon and into the evening hours.
Otherwise, relatively weak high pressure ridging will remain
across the northern gulf waters, with the associated gradient
producing gentle to moderate anticyclonic flow through Fri.

CARIBBEAN SEA...

Two tropical waves are moving across the basin. Refer to the
section above for details. An upper level trough extends from
eastern Cuba southwestward to just east of northeastern Honduras.
Water vapor imagery indicates plentiful deep layer moisture along
and to the northwest of this trough, and it is where isolated
showers and thunderstorms are occurring. Scattered moderate
isolated strong convection has increased over the far southwestern
Caribbean south of 11N between 77W and 82W mainly due to low-level
wind speed convergence, with the added factor of the eastern
segment of the eastern Pacific monsoon trough that stretches east-
northeastward to the far southwestern Caribbean along 09N and to
the typical climatological low found over northwestern Colombia
presently located just offshore that coast at 09N76W.

A slighter tighter pressure gradient behind the tropical wave
along 77W will help induce strong to near gale force northeast to
east trade winds over the south-central Caribbean waters off the
coast of Colombia and across the Gulf of Venezuela tonight. The
strong trades are forecast to reach northward to 15N. Moderate to
fresh trades will continue elsewhere through Fri as little overall
changes are expected with the present synoptic set-up through
Fri.

ATLANTIC OCEAN...

Two tropical waves are moving across the basin. Refer to the
section above for details. A surface trough is analyzed from
29N61W to 21N68W. A shear axis is evident by model and satellite
winds to be situated northwest of the trough from 32N65W to 25N70W
to east-central Cuba. Satellite imagery shows increasing scattered
showers and thunderstorms within 180 nm to the northwest of the
trough between 65W and 69W. Isolated showers and thunderstorms
are seen over the western portion of the basin west of about 75W.
This activity as well as that to the northwest of the surface
trough are expected to last through tonight and into Thu. Another
trough moving westward around 15 kt is along 52W from 17N to 30N.
No deep convection is noted with this trough, only isolated
showers within 120 nm east of the trough from 21N to 26N. A 1025
mb high center is analyzed north of 31N and extends a ridge across
the remainder of the basin. Saharan dust and associated dry air,
although not as dense as in previous days, is noted mainly east of
about 60W on GOES-16 GEO color dust imagery. The dust is keeping
convection rather limited, to non-existent, outside across the
eastern and central Atlantic waters, except as described above
near the the ITCZ region.

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

$$

JA/ERA
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