[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 131737
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
137 PM EDT Sun Aug 13 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 1200 UTC surface analysis and satellite imagery through
1715 UTC.

...SPECIAL FEATURES...

Tropical Depression Eight is centered near 27.4N 71.5W at 13/1500
UTC, or about 455 nm SW of Bermuda moving toward the north-
northwest, or 335 degrees, at 11 kt. A turn toward the north is
forecast to occur tonight, followed by a turn toward the north-
northeast on Monday. Estimated minimum central pressure is 1011
mb. Maximum sustained wind speed is 30 kt with gusts to 40 kt.
Numerous moderate and scattered strong convection is noted within
150 nm eastern semicircle of the low center. The system is
expected to remain east of the United States, reaching tropical
storm intensity later today or tonight. See latest NHC forecast/
advisory under AWIPS/WMO headers MIATCMAT3/WTNT23 KNHC for more
details.

...TROPICAL WAVES...

A tropical wave that has emerged off the west coast of Africa is
along 19W/20W from 09N-21N. A 1010 mb low pres is analyzed along
the wave axis near 13.5N19.5W. A cluster of moderate to isolated
strong convection is within about 180 nm west quadrant of low
center. Scattered moderate convection is elsewhere from 10N-16N
between 17W-23W. The low is forecast to move westward over the
next couple of days and merge with a broad area of low pressure
located southwest of the Cabo Verde Islands. Environmental
conditions are expected to become more conducive for development
of this system later this week while it moves westward at about
10-15 kt over the tropical Atlantic. Currently, there is a medium
chance for tropical cyclone formation through 5 days.

A large tropical wave is in the eastern Atlantic moving west at
15-20 kt. It axis extends from 21N33W to 08N34W. The wave shows up
very well on the TPW animation and 700 mb streamline analysis.
Scattered moderate convection is noted where the wave meets the
monsoon trough from 08N-12N between 34W-40W. A broad low pres area
is noted along the wave axis. African dust surrounds the wave.

The axis of a tropical wave is along near 52W/53W from 09N to
21N. The wave is moving W at 15-20 kt. It coincides with a 700 mb
trough, and is well depicted in the moisture product. There is
limited convection associated to this wave. It is forecast to
move across the waters between 55W and the Lesser Antilles this
afternoon and tonight, and across the eastern Caribbean on Monday.

A tropical wave is in the western Caribbean and extends from the
westernmost tip of Cuba across Honduras, Nicaragua, and Costa Rica
into the Eastern Pacific region. Scattered moderate convection is
noted in the wake of the wave axis and mainly from 10N-17N
between 82W-85W.

...ITCZ/MONSOON TROUGH...

The monsoon trough extends from the coast of Africa near 13N17W
to 12N30W to 09N45W. The Intertropical Convergence Zone continues
from 09N45W to 08.5N50W. Aside from convection associated with
the tropical waves, scattered moderate isolated strong convection
is noted from 10N-15N between 23W-30W. This convective activity is
ahead of the next tropical wave located along 19W/20W.

...DISCUSSION...

GULF OF MEXICO...

As of 1500 UTC, a surface trough is analyzed over the NE Gulf and
extends from the Florida Panhandle at 30N85W to 28N90W. A recent
scatterometer pass indicate the wind shift associated with this
trough. Scattered showers with embedded thunderstorms are near the
trough axis, affecting the Gulf waters N of 26N between 85W-90W.
The trough will lift northward on Monday, but abundant moisture is
expected to persist over the NE Gulf in an southerly wind flow
between the trough inland and a ridge to the south that currently
extends west across the central Gulf. The ridge is producing a
light to gentle anticyclonic flow across the remainder of the
Gulf. The one exception is an area of moderate winds west of a
thermal trough that moved off the Yucatan Peninsula into the
southwest Gulf. The ridge will remain across the Gulf waters the
next several days. Southerly return flow will freshen over western
Gulf by midweek.

A thermal trough will develop each evening over the Yucatan
Peninsula, shifting westward into the southwest Gulf during the
overnight hours, and dissipating over this area each morning.
Locally higher winds can be expected west of the trough axis.

CARIBBEAN SEA...

Please see above for more on the tropical wave moving through the
western Caribbean. The tropical wave will continue to propagate
westward, reaching the Yucatan Peninsula tonight. Latest
scatterometer data provide observations of moderate to fresh winds
across the east and central Caribbean, while mainly light and
variable winds are noted over the NW Caribbean. The pressure
gradient is forecast to tighten early this week as the Atlantic
ridge builds westward in the wake of currently T.D. Eight. This
will allow for the trade winds to expand northward across the
central Caribbean to near 17N by Monday morning. Expect building
seas to 8-10 ft with the strongest winds across the south-central
Caribbean. These marine conditions will persist across the basin
through midweek.

Convection continues to flare up across the SW Caribbean. A
cluster of moderate convection is noted from 10N-13N between
76W-79W. An ASCAT pass shows an area of fresh to locally strong
winds over the SW Caribbean likely associated with this
convective activity. A diffluent pattern aloft, associated with an
upper-level anticyclonic circulation situated near 13N76W
continues to enhance this convective activity. Shallow moisture
embedded in the trade wind flow is noted elsewhere.

...HISPANIOLA...

Daytime heating, local sea breezes and mountain upslope lifting
will combined with available moisture to produce isolated showers
and thunderstorms mainly during the afternnon and evening hours.
The next tropical wave is forecast by the computer model to affect
the island on Tuesday.

ATLANTIC OCEAN...

Please see the Special Features section above for more on
Tropical Depression Eight, and the Tropical Wave section above
for more on the tropical waves propagating across the tropical
Atlantic waters. The remainder of the forecast area is under the
influence of the Bermuda-Azores high that is a subtropical high
located over the Atlantic Ocean. This high pressure system will
build westward across the forecast region as currently T.D. Eight
moves northward. Winds are forecast to increase between the
eastern tropical wave and strengthening subtropical high to the
north. The fresh winds will shift along with the tropical wave as
it propagates westward the next couple of days. The Saharan Air
Layer tracking product from CIMSS continues to indicate abundant
african dust N of 20N E of 30W and between 30W and 50W.

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

$$
GR
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