[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 150005
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
805 PM EDT Fri Jul 14 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
2345 UTC.

...TROPICAL WAVES...

A central Atlantic tropical wave has its axis along 43W/44W south
of 15N, moving westward 20 knots. The majority of the wave
is shrouded by dry Saharan air as depicted in the latest
METEOSAT-9 Saharan Air Layer imagery. Only convection noted with
this wave is south of 10N to the ITCZ region, and consists of the
scattered moderate type intensity convection from 07N to 10N
between 42W-45W.

A Caribbean Sea tropical wave has its axis along 63W/64W south of
18N. This wave is moving westward at an estimated speed of 19 kt
over the past 24 hours. The wave exhibited a well pronounced
northeast to southeast wind shift in the upper air sounding from
Trinidad this morning at 12Z. Last visible satellite imagery
continued to show a pretty well-defined cloud structure to the
wave, with what appears to be a low-level vorticity maximum on the
southern portion of the wave axis at 12.5N64W. Scattered moderate
convection is within 30 nm of 14N64W. Scattered showers and
isolated thunderstorms are elsewhere east of the wave axis. This
wave is forecast to move across the rest of the eastern Caribbean
through Saturday and reach the central Caribbean by Saturday
evening. Increasing moisture along scattered showers and isolated
thunderstorms will follow the wave. Some of the shower and
thunderstorm activity may contain gusty winds.

A central Caribbean Sea tropical wave has its axis along 74W,
moving westward at about 15 knots. The northern portion of the
wave axis is just west of Haiti. A small upper low is noted
over the northern part of the wave, with an associated trough
extending from it over the remainder of the wave. Subsidence
aloft with dry is over the this wave's environment for the time
being. Deep convection that occurred during this afternoon just
east of the wave has dissipated. Only isolated showers and
thunderstorms are within 150 nm east and 60 nm west of the wave
axis north of 15N. The wave will move across the rest of the
central Caribbean through early Saturday and the western portion
of the sea later on Saturday and through Sunday. The wave may
acquire more in the way of moisture along with shower and
thunderstorm activity as it moves through the western Caribbean.

...ITCZ/MONSOON TROUGH...

The Monsoon Trough axis extends from passes through coastal
sections of Guinea-Bissau near 12N16W and continues to 11N22W
where scatterometer data indicates the ITCZ then begins and
continues to 08N34W to 06N40W to just west of the tropical wave
along 43W/44W. It resumes just west of the same wave to near
06N54W. Scattered moderate isolated strong convection is within
120 nm south of the axis between 52W-54W. Scattered moderate
convection is within 180 nm north of the axis between 37W-42W and
within 240 nm north of the axis between 45W-48W.

...DISCUSSION...

...THE GULF OF MEXICO...

A weak pressure pattern is present across the area. A small upper
low is noted just northwest of the Yucatan Peninsula with a
trough reaching to the north-central Gulf near southeastern
Louisiana. A very moist and unstable air mass in place over just
about the entire Gulf, except in the far SW Gulf where some dry
air is noted aloft. A surface trough, most likely a result of the
upper trough, is analyzed from near 29N87W to 24N86W. Scattered
showers and thunderstorms are occurring north of 24N east of 92W,
while scattered showers and isolated thunderstorms are north of
24N west of 92W. Isolated showers and thunderstorms are south of
92W. Isolated showers are south of 24N and west 92W. Moisture
guidance suggests that ample moisture will continue over much of
the Gulf through the weekend maintaining good chances for more
scattered shower and thunderstorm activity.

...THE CARIBBEAN SEA...

A couple of tropical wave are moving through the Caribbean Sea.
See above for details on these features. The pressure gradient
throughout remains fairly weak. A small upper level low is just
south of Haiti, with a sharp upper trough extending from it to the
coast of Colombia near 11N71W. A small upper level anticyclone is
over the far SW Caribbean Sea near 11N80W. Broad anticyclonic
flow covers the western Caribbean, and the eastern part of the sea
to the east of the upper trough. The far NW Caribbean is under
the eastern fringe of upper cyclonic flow related to the upper low
that is situated just northwest of the Yucatan Peninsula. The
anticyclonic flow over the eastern Caribbean is transporting upper
debris clouds attributed to the convective activity east of the
eastern Caribbean wave north-northeastward towards the NE
Caribbean and Leeward Islands. Abundant moisture over the western
Caribbean is producing scattered showers and isolated
thunderstorms there, including the far SW Caribbean where the
eastern segment of the eastern Pacific monsoon trough is analyzed
across Costa Rica and Panama.

...HISPANIOLA...

Deep convection that earlier occurred with the tropical wave
that is just west of Haiti has dissipated, however, deep
convection remains over much of the northwestern section
of Hispaniola. Isolated showers and weakening are elsewhere
over the island and nearby waters. Moisture associated
with the eastern Caribbean wave will begin to approach
the eastern part of the Hispaniola on Saturday afternoon,
and spread across the remainder of the island into Sunday.
With this scenario expected, shower and thunderstorm activity
should become more widespread over portions of the island as
well as over the nearby waters.

...THE ATLANTIC OCEAN...

A nearly stationary upper level low is seen near 28N65W, with a
trough stretching from it southwestward to 24N66W to 22N76W to
western Cuba. Another upper level low, this one is larger, is
over the eastern Atlantic near 28N43W and is moving westward.
A trough extends from this low southwestward to 21N46W and
southward to a weak and small upper low near 17N47W. Upper
level moisture, in the form of scattered to broken high clouds,
is streaming northeastward from the eastern Caribbean Sea in
southwesterly to westerly flow between the upper low near 28N65W
and the anticyclonic flow over the eastern Caribbean Sea
associated with a small anticyclone near 15N58W. Abundant dry
air covers the central and eastern Atlantic as observed in water
vapor imagery, and is confirmed by the Meteosat-9 imagery that
depicts abundant dry and stable air over those portions of the
Atlantic. It is also where an extensive Saharan Air layer is
present with dust.

At the surface, a nearly stationary 1028 mb high center analyzed
34N48W extends a ridge southwestward to 32N67W and to just east of
northeastern Florida. A surface trough is along a position from
29N71W to 24N74W. The northern portion of the Caribbean tropical
wave along 74W extends northward to the SE Bahamas. Scattered
showers and thunderstorms are observed south of 26N between 68W-
75W, and also north of 25N between 57W-62W. Scattered showers and
isolated thunderstorms are elsewhere south of 30N between 56W-
70W, and south of 28N between 62W-77W. Isolated showers and
thunderstorms are noted over the remainder of the area west of
56W. The northern portion of the tropical wave will move
across the rest of the southern Bhamas through Saturday, and
across the far southwestern waters late Saturday through Sunday,
while the ridging changes little.

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

$$
Aguirre
This weather bulletin was brought to you by:
www.nashvilleweather.net