[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 211756
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
156 PM EDT Sat Jul 21 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
1500 UTC.

...TROPICAL WAVES...

A tropical wave is starting to move off the coast of Africa this
afternoon, accompanied by thunderstorms from Sierra Leone to
Senegal.

A tropical wave is in the eastern Atlantic with axis extending
from 05N-22N along 32W, moving W at 10-15 kt. Saharan dry air and
dust continue to prevail in the wave's environment as shown by
CIRA LPW and GOES-16 RGB imagery. This is inhibiting large scale convection
at this time, although isolated showers are noted where the
tropical wave intersects the monsoon trough.

A tropical wave is in the central Atlantic with axis extending
from 05N-21N along 48W, moving W at 10-15 kt. The wave is moving
across an extensive area of Saharan dry air, which is hindering
convection at the time.

A low amplitude and low latitude tropical wave is moving across
Venezuela into eastern Colombia with axis extending from 00N-10N
along 67W, moving W at 10-15 kt. Numerous moderate to isolated convection
is observed across the Orinoco Plains of eastern Colombia. The
tropical wave will lose some definition as it moves across the
Andes through Sun, but may emerge into the eastern Pacific off
Colombia Mon.

A tropical wave is in the west-central Caribbean from western
Panama to central Cuba. The tropical wave is interacting with
trade convergence to support thunderstorms from central Panama to
off Costa Rica to eastern Nicaragua.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends from the coast of Mauritania in W
Africa near 18N15W and continues to 10N25W to 09N40W. The ITCZ
begins near 09N40W and continues to Guyana near 08N60W. Scattered
moderate convection is noted from 07N to 09N between 28W and 32W.

...DISCUSSION...

GULF OF MEXICO...

A vigorous short wave trough in the mid to upper levels of the
atmosphere is supporting a large area of thunderstorms moving
through southwest Georgia and the eastern Florida Panhandle. The
storms will move across the Florida Big Bend area of the far
northeast Gulf over the next two to three hours, catching up to a
surface trough moving south into central Florida and the east
central Gulf. Farther south, a few thunderstorms remain active
approximately 120 nm southwest of Tampa Bay. Buoy observations and
recent scatterometer data show moderate to fresh W to NW winds
over the northeast Gulf, with 2 to 4 ft seas. Stronger gusts and
locally higher seas are possible near the thunderstorms emerging
into the Big Bend area. Elsewhere, 1017 mb high pressure is
centered over the south central Gulf with a surface ridge
extending toward the Texas coast. This is maintaining gentle
breezes and 1 to 3 ft seas.

The weak boundary across Central Florida will gradually settle
southward over the next few days, bringing moderate west-
southwesterly flow. The increasing westerly fetch will bring
gradually higher seas in the offshore Gulf waters by early next
week. Showers and thunderstorms will persist over the eastern Gulf
through Sun. A surface trough will move off the Yucatan Peninsula
into the Bay of Campeche each evening, accompanied by fresh
nocturnal winds and scattered showers. Otherwise little change is
expected.

CARIBBEAN SEA...

A scatterometer pass from 14 UTC showed strong to near-gale force
trade winds of the central and northeast coasts of Colombia,
reaching as far north as 15N. Seas are estimated to be 10 to 13 ft
in this area. Aside from the thunderstorms over the southwest
Caribbean, little to no shower or thunderstorm activity is noted
due to the presence of Saharan dust and dry air, mainly impacting
the eastern Caribbean.

For the forecast, high pressure north of the area will support
strong to near gale force winds in the south-central Caribbean
through tonight before winds diminish.

ATLANTIC OCEAN...

Mid to upper-level diffluent flow between a ridge in the west
Atlantic and a trough along the eastern U.S. continue to support
scattered showers and tstms in a line from roughly Grand Bahama to
north of 31N75W. Similarly divergent flow aloft between the upper
ridge and an upper low farther east near 28N57W will support
scattered showers and thunderstorms northeast of the Turks and
Caicos Islands within 90 nm of of 24N69W. Saharan dust is evident
to the south of this clusters of thunderstorms, presenting the
potential for strong gusty winds accompanying these thunderstorms.
For the forecast, high pressure ridge across the northern waters
will remain in place through Sun before lifting N Mon through
Wed. Scattered showers and thunderstorms will persist N of 27N
and E of 78W through early next week.

Fair weather is elsewhere across the Atlantic, however hazy
conditions are expected S of 26N as the extensive Saharan Air
Layer outbreak moves across the Atlantic tropical waters.

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

$$
Christensen
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