[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 112321
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0005 UTC Sun Sep 12 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 1800 UTC surface analysis and satellite imagery through
2300 UTC.

...SPECIAL FEATURES...

Divergence aloft on the southeast side of a broad upper low over
central Mexico is enhancing clusters of showers and thunderstorms
across the southwest and south-central Gulf of Mexico. This
forcing was also assisted by lower to mid-level influence from the
northern extent of a tropical wave passing through the region. No
distinct area low pressure has formed yet along a sharp surface
trough just off the Veracruz coast and over the warm waters of
the Bay of Campeche, but may shortly as this pattern persists. Although
upper-level winds are not conducive for development currently,
they are expected to become more favorable for the system during
the next day or so. A tropical depression is likely to form on
Sunday or Monday while the disturbance moves northwestward and
then northward near the coast of northeastern Mexico. Further
development will be 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. 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.

An area of low pressure with an estimated pressure of 1011 mb has formed
near the Cabo Verde Islands near 15.5N 22.5W. This is at the intersection
of the monsoon trough with the axis of a tropical wave extending
along 22.5W from 21N southward, moving W at 15-20 kt. There continues
to be a concentrated but disorganized area of showers and thunderstorms
from 14N-18N between 21W-25W, which is includes most of the 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,
this disturbance is likely to bring gusty winds and locally heavy
rain across the Cabo Verde Islands through tonight. The chance of
tropical cyclone formation within the next 48 hours is medium.

...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 is along 44W from 06N-22N, moving W at
15 kt. The wave is surrounded by dry Saharan air, which is
inhibiting convection at this time.

A tropical wave is moving into the eastern Caribbean with and axis
along 63W from 06N-21N, moving W at 20 kt. This wave is moving
westward in sync with an upper- level trough. Surface observations
from the Leeward Islands to Puerto Rico show decent cyclonic
turning at the surface associated with this tropical wave and
upper trough. Divergent flow aloft is supporting scattered
moderate convection from 16N- 20N between 63W-67W, impacting
mainly the Virgin Islands and Puerto Rico.

A Caribbean tropical wave has an axis along 80W from 15N
southward, moving W at 10-15 kt. A few showers may be active off
Costa Rica, but elsewhere no significant convection is noted over
the southwest Caribbean related to this tropical wave.

...MONSOON TROUGH/ITCZ...

The monsoon trough passes through the coast of Mauritania near
19N16W to the 1011 mb low pressure near 15.5N 22.5W, to 06N35W.
The ITCZ continues from 06N35W to 07N42W. No significant
convection is observed near the monsoon trough or ITCZ, other than
the showers impacting the Cabo Verde Islands.

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 near the mouth of the Rio
Grande southward off the Tamaulipas and Veracruz coasts to 20N95W
in the Bay of Campeche. A weakening stationary front extends from
Cedar Key Florida near 28N94W. Scattered moderate and isolated
strong convection cover much of the Gulf of Mexico south of 26N.
An area of numerous moderate to scattered strong convection is in
the Bay of Campeche from 18N-21N between 90W-94W, associated with
the tropical wave and the effects of the upper low to the west.
Fresh NW winds are noted along the coast of Veracruz south of 20N.
Elsewhere, buoy data and recent scatterometer satellite data
indicate mostly gentle to moderate E winds across the basin,
occasionally becoming fresh in large clusters of convection
primarily over the warmer Loop Current in the south-central Gulf
and over parts of the Bay of Campeche. Associated seas in the
south-central Gulf may be reaching 4 to 6 ft, with generally 2 to
4 ft elsewhere.

For the forecast, please see the Special Features section above
for more information about the potential for tropical cyclone
development in the western Gulf. Elsewhere, the frontal boundary
over the northern Gulf will prevail through tonight supporting a
few showers and thunderstorms across the region.

CARIBBEAN SEA...

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

The Atlantic ridge north of the area is maintaining fresh to
strong trade winds off Colombia from 10N to 15N between 72W and
80W, with 6 to 9 ft seas. Generally moderate to fresh trade winds
and 4 to 6 ft seas persist elsewhere, except for moderate to fresh
SE winds and 3 to 5 ft seas over the northwest Caribbean. Other
than the aforementioned showers in the northeast and southwest
Caribbean, a few showers may be occurring near the Yucatan
Channel, with no significant convection noted elsewhere.

For the forecast, the Atlantic ridge will continue to build
westward across the Caribbean, bringing an increase in the trade
wind flow through weekend. Fresh to strong winds will persist
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 late Sun. Scattered
showers and thunderstorms across the NW Caribbean are expected to
reduce in coverage through tonight.

ATLANTIC OCEAN...

A cold front extends from 32N66W to 31N67W, where it transitions
to a stationary front to near Cape Canaveral Florida. A few
showers and thunderstorms are noted off the east coast of Florida
south of the frontal boundary to Grand Bahama Island. A ridge
extends from 1026 mb high pressure to near 27N65W. Scattered
showers and a few thunderstorms are noted northeast of Leeward
Islands, associated with the upper low centered north of Puerto
Rico. Gentle to moderate NE to E winds are noted north of 25N into
the subtropical ridge. Recent scatterometer and buoy data showed
fresh winds and seas to 8 ft near a surface trough east of the
Windward Islands reaching from 11N55W to 16N52W. Moderate to fresh
NE winds and 5 to 7 ft seas are noted north of the low pressure
in the Cabo Verde Islands covering the area from 15N to 25N
between 25W and 35W. Elsewhere buoy data and recent scatterometer
satellite data confirm mostly moderate trade winds are noted south
of 25N with 5 to 7 ft seas.

For the 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.

$$
Christensen
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