AXNT20 KNHC 211746
Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1805 UTC Thu Oct 21 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
The axis of a tropical wave is along 40W, south of 17N and it is
moving W at 10-15 kt. The wave is embedded in Saharan dry air,
suppressing the development of showers and thunderstorms. However,
satellite imagery depict a broad surface trough with a few light
A tropical wave has been added to the surface analysis based on
wave guidance and satellite imagery. The axis of the tropical wave
is along 54W, south of 17N. Scattered moderate to isolated strong
convection is noted within 150 nm on both sides of the wave axis,
south of 10N. The wave is embedded in Saharan dry air N of 10N.
The axis of a tropical wave is along 65W, south of 21N and it is
moving W at 10-15 kt. This wave is in the leading edge of a large
area of Saharan dry air. Scattered moderate convection is observed
within 100 nm on both sides of the wave axis, mainly south of 14N.
The axis of a tropical wave is along 73W, south of 21N, extending
from the Haiti to N Colombia, and it is moving W at 10-15 kt.
A few showers are noted near the wave axis.
The monsoon trough extends across the coast of Senegal from
14N17W to a 1012 mb low pressure near 13N19W to 03N26W. The ITCZ
continues from 03N26W to 02N44W. Aside from convection noted in
the tropical waves section above, scattered moderate convection
is noted from 05N to 10N and E of 22W.
GULF OF MEXICO...
The 1025 mb subtropical ridge near Bermuda extends into the Gulf
of Mexico. A recent scatterometer satellite pass indicate fresh to
locally strong NE winds occurring in the Florida Straits and SE
Gulf, mainly within 100 nm of the Florida Keys and the NW Cuban
coast. Moderate or weaker anticyclonic winds are present in the
rest of the Gulf. A surface trough extends along 94W from 17N to
22N and it is producing isolated moderate convection over the W
Bay of Campeche. A few showers are also noted in the SE Gulf and
within 60 nm of the N Gulf coast. Seas of 3-6 ft are found E of
92W, with the highest seas occurring in the Florida Straits. Seas
of 1-3 ft prevail elsewhere in the basin.
For the forecast, the aforementioned ridge will dominate the Gulf
waters through early next week. Moderate to fresh easterly winds
are expected across the SE Gulf into tonight. Gentle to moderate
winds will prevail elsewhere.
A surface trough near the E coast of Yucatan is producing
scattered showers and isolated thunderstorms within 60 nm of the
trough axis, affecting portions of the Gulf of Honduras. A few
showers are also found in the central and SW Caribbean, mainly
south of 17N. Recent satellite-derived winds show fresh to locally
strong trades in the SE Caribbean, likely associated with the
leading edge of the dry Saharan airmass entering the region.
Moderate or weaker trades are present in the rest of the Caribbean
Sea. Seas of 4-6 ft are found in the E, central and SW Caribbean,
with the highest seas occurring in the SE Caribbean. Seas of 2-4
ft are prevalent elsewhere.
For the forecast, high pressure N of the area will support fresh to
locally strong trades E of the Windward Islands through Sun
night. During this period, moderate to fresh winds are expected
over the south- central Caribbean, with winds reaching locally
strong in the Venezuela basin. Gentle to moderate tradewinds will
The main feature of interest in the tropical Atlantic is a
dissipating stationary front that stretches from 31N42W to 26N54W
and then continues as a trough to the SE Bahamas. Scattered
moderate to isolated strong convection is occurring within 120 nm
of the trough axis, especially from 52W to 72W. Scatterometer
satellite data depict fresh to strong NE winds N of the trough
axis to 27N and between 56W to the SE coast of Florida. Seas of
4-7 ft are present W of 60W, with the highest seas occurring in
the area of strong winds. A weak surface trough is found from
18N33W to 26N35W, but there is no deep convection associated with
The rest of the basin is patrolled by the robust 1025 mb high pressure
system near Bermuda and the strong 1030 mb high pressure system
near the Azores, resulting in fairly tranquil weather conditions.
The pressure gradient resulting from these high pressures and
lower pressures over South America is causing a large area of
fresh and strong trades S of 20N and between 37W and the Lesser
Antilles. Another area of fresh to strong NE winds is noticed in
the satellite-derived wind data in the NE Atlantic, N of 24N and E
of 28W. Seas in both regions are 6-9 ft. Moderate or weaker winds
and seas of 4-7 ft prevail in the rest of the basin.
The Cumbre Vieja volcano, on the island of La Palma in the
Canary Islands, has been erupting since 19 September 2021. Ash
emission is on-going. Moderate to high volcanic ash is expected
in the vicinity of the volcano. Elsewhere, light volcanic ash
concentration is drifting south. Marine and aviation interests
should monitor this ongoing situation by reading the Volcanic Ash
Advisory issued by Meteo-France at http://vaac.meteo.fr/volcanoes
For the forecast west of 65W, high pressure will shift eastward
across the W Atlantic along 31N-32N into Fri, producing moderate
to fresh winds. Surface troughing will then prevail over the area
through early next week.