[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 111806
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1805 UTC Sat Sep 11 2021

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 31N. The following information is based on satellite
imagery, weather observations, radar and meteorological analysis.

Based on 1200 UTC surface analysis and satellite imagery through
1700 UTC.

...SPECIAL FEATURES...

A tropical wave extends from 21N92W to Mexico near 18N93W and
into the Pacific Ocean near 16N94W. An upper-level trough
extends from the coast of Texas to central Mexico. Upper-level
diffluence east of the upper-trough in combination with the
tropical wave are producing disorganized scattered moderate and
isolated strong showers and thunderstorms over portions of the
southern and central Gulf of Mexico, and southeastern Mexico. A
recent ASCAT pass shows fresh E to SE winds between the wave
axis and the west coast of the Yucatan Peninsula. Upper-level
winds are expected to become more favorable during the next day
or so, and a tropical depression is likely to form Sunday or
Monday while the disturbance moves northwestward and then
northward near the coast of northeastern Mexico. Further
development is possible through the middle of next week if it
remains over water, and interests along the western and
northwestern Gulf coast should monitor the progress of this
system. Expect an increase in winds and seas along these regions
with this system. Regardless of development, the disturbance is
expected to produce heavy rain across portions of the Yucatan
Peninsula through today, which may lead to flash flooding. By
late this weekend, heavy rain will likely reach portions of the
western Gulf coast, including coastal Texas and Louisiana
through the middle of next week. Localized significant rainfall
amounts are possible, potentially resulting in areas of flash
and urban flooding. The chance of tropical cyclone formation
within the next 48 hours is high.

A tropical wave with an axis along 21W from 21N southward is
moving W at 15-20 kt and is producing a concentrated but
disorganized area of showers and thunderstorms from 12N-17N
between 18W-23W, which is now just reaching the eastern Cabo
Verde Islands. Environmental conditions appear generally
conducive for gradual development, and a tropical depression is
likely to form late this weekend or early next week while the
system moves westward over the far eastern Atlantic. Regardless
of development, gusty winds and locally heavy rain are expected
across the Cabo Verde Islands through tonight. The chance of
tropical cyclone formation within the next 48 hours is medium.

Larry has transitioned to an extratropical cyclone as of 1500
UTC today, and the final NHC advisory has been issued. The
position is near 54.0N 48.2W at 1500 UTC, or about 480 nm NNE of
Cape Race, Newfoundland, moving NNE at 42 kt. Estimated minimum
central pressure is 963 mb. Maximum sustained wind speed is 60
kt with gusts to 75 kt. Larry is expected to merge with another
extratropical low tonight or early Sunday. Significant swells
from Larry will continue affecting portions of the east coast of
the United States and Atlantic Canada through tonight. These
swells are likely to cause life-threatening surf and rip current
conditions. Please see the final NHC
advisory at www.hurricanes.gov for more details.

...TROPICAL WAVES...

See the section above for details on the two tropical waves with
potential for development, currently located along 21W and 92W.

An Atlantic tropical wave has an axis along 42/43W from 05N-23N,
moving W at 15 kt. The wave is surrounded by dry Saharan air,
which is inhibiting convection at this time.

An Atlantic tropical wave has an axis along 61W from 05N-21N,
moving W at 20 kt. This wave is moving westward in sync with an
upper-level trough. Satellite imagery and ASCAT data show broad
surface curvature with this wave. Scattered moderate convection
is noted from 16N-22N between 56W-66W.

A Caribbean tropical wave has an axis along 78W from 15N
southward, moving W at 10-15 kt. The interaction of this wave
with the E Pacific monsoon trough is enhancing scattered
moderate to isolated strong convection over the SW Caribbean,
south of 12N.

...MONSOON TROUGH/ITCZ...

The monsoon trough passes through the coast of Mauritania near
19N16W to 13N26W to 06N34W. The ITCZ continues from 06N34W to
06N41W. Aside from the convection noted in the sections above,
scattered moderate convection is seen from 05N-08N between
26W-38W.

GULF OF MEXICO...

See the Special Features section above for details on the
tropical wave over the eastern Bay of Campeche and a description
of the upper-level trough in the area. In addition to those
features, a surface trough extends from NE Mexico near 26N98W to
20N95W. A stationary front extends from Cedar Key Florida near
29N83W to 28N94W. Expect the frontal boundary to prevail through
Sunday. Scattered moderate and isolated strong convection cover
much of the Gulf of Mexico south of 27N. An area of numerous
moderate to scattered strong convection is in the Bay of
Campeche from 18N-21N between 92W-95W, associated with the
tropical wave. Other than the fresh winds in the Bay of
Campeche, mainly moderate wind speeds prevail elsewhere. Recent
buoy observations and altimeter data show seas of 3 to 4 ft
across much of the basin, but seas up to 5 ft could be occurring
in the eastern Bay of Campeche.

CARIBBEAN SEA...

Please see the Tropical Waves section above for details on the
tropical waves along 61W and 78W.

Scattered moderate convection is occurring over the NW Caribbean
north of 20N west of 84W due to the tropical wave over the
eastern Bay of Campeche. That convective activity will diminish
later today. Scattered tstorms are occurring near the Virgin
Islands, Puerto Rico and the Dominican Republic due to an
upper-level low/trough moving westward across the area.
Subsidence and drier air is found over most of the central
Caribbean. A recent ASCAT pass shows strong trades in the
south-central Caribbean from 11N-15N between 71W-78W, where seas
are 6 to 9 ft. Buoy 42058 near 14.4N 74.8W is reporting E wind
21 kt and seas of 8 ft at 1700 UTC. Fresh to strong east to
southeast winds are seen in the Gulf of Honduras, where seas are
5 to 6 ft. Moderate trades prevail across the remainder of the
basin, with 3 to 5 ft seas.

For the forecast, the Atlantic ridge will continue to build
westward across the Caribbean, bringing an increase in the trade
wind flow this weekend. Fresh to strong winds will occur
offshore Colombia and in the Gulf of Venezuela, mainly at night
through Sun. Fresh to strong winds are also likely in the late
evening in the Gulf of Honduras through Sun.

ATLANTIC OCEAN...

West of 60W: A cold front extends from 31N67W to 30N69W, with a
stationary front from 30N69W to Cape Canaveral Florida. Isolated
showers and thunderstorms are near and north of the front.
Expect the showers and storms to linger through Mon while the
front remains over the area. Moderate NE to E winds are north of
the front. Gentle E to SE winds are south of the front. An
upper-level low spinning near 21N64W is moving westward along an
upper-level trough. Isolated thunderstorms cover the area south
of 25N between 62W-79W. Gentle winds prevail from 24N-29N, due
to weak surface ridging. ASCAT shows moderate trade winds south
of 24N and west of 65W. Seas of 4 to 6 ft prevail over northern
portions of the area as the swell from Larry subsides. Seas are
3-5 ft south of 25N west of 65W.

East of 60W: A surface trough is analyzed from 11N53W to 17N51W.
Scattered moderate convection is seen from 13N-18N between
49W-56W. A surface high pressure ridge extends across the
subtropics from 29N22W to 28N60W with gentle wind speeds north
of 27N. Fresh trades are from 20N-25N between 20W-45W, and from
14N-22N between 49W-61W. Seas are 5 to 8 ft in the area of fresh
winds.

Forecast west of 60W: An area of low pressure is expected to
form near the southeastern Bahamas in a few days. Gradual
development of this system is possible thereafter as it moves
northwestward across the western Atlantic. See the latest NHC
Tropical Weather Outlook at www.hurricanes.gov for details.

$$
Hagen
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