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Atlantic Tropical Weather Discussion



000
AXNT20 KNHC 281055
TWDAT 

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 UTC Tue Sep 28 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 0600 UTC surface analysis and satellite imagery through 
1030 UTC.

...SPECIAL FEATURES... 

Hurricane Sam was centered near 17.2N 53.9W at 28/0900 UTC or 530
nm E of the Northern Leeward Islands moving NW at 8 kt. Estimated
minimum central pressure is 953 mb. Maximum sustained wind speed 
is 115 kt with gusts to 140 kt. Peak seas near the center are 
currently around 30 ft and are forecast to increase to near 38 ft
by Thu. Satellite imagery continues to show a well-defined eye. 
Numerous moderate to scattered strong convection is within 100 nm
of the center in the E and within 60 nm of the center in the W 
quadrant. Scattered moderate convection is within 150 nm of the 
center. Sam is moving toward the northwest and is expected to 
continue for the next few days, with an increase in forward speed 
beginning on Thursday. A turn toward the north is expected by 
Friday. On the forecast track, Sam will pass well to the northeast
of the northern Leeward Islands on Wednesday and Thursday. Some 
fluctuations in intensity are expected during the next couple of 
days, but Sam is forecast to remain a major hurricane through late
this week. Swells generated by Sam will impact the Lesser 
Antilles for the next several days. Swells are expected to reach 
Bermuda and the Bahamas within a couple of days, and then spread 
to the United States east coast late this week. These swells could
cause life- threatening surf and rip current conditions. Please 
read the latest High Seas Forecast issued by NHC at 
http://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest NHC 
Public Advisory and Forecast/Advisory at 
https://nhc.noaa.gov/cyclones/

A well-defined low pressure system associated with the remnants 
of Peter is located a few hundred miles east of Bermuda. A few
showers and isolated thunderstorms are noted well to the NE of the
center. Although strong upper-level winds are likely to prevent 
significant development, this system could still become a short-
lived tropical depression later today or tonight while it moves 
northeastward at about 10 mph. By Wednesday, conditions are 
expected to become unfavorable for further development. This 
system has a medium chance of development during the next 48 
hours. Please refer to the latest NHC Tropical Weather Outlook at 
www.hurricanes.gov for more details.

A broad area of low pressure located several hundred miles 
southwest of the Cabo Verde Islands is producing a large area of 
disorganized showers and thunderstorms. Environmental conditions are 
conducive for further development, and a tropical depression is 
likely to form during the next day or two while the system moves 
westward to west-northwestward at 10 kt over the central tropical
Atlantic. This system has a high chance of development during the
next 48 hours. Please refer to the latest NHC Tropical Weather 
Outlook at www.hurricanes.gov for more details.

A far eastern Atlantic tropical wave located over the far eastern
tropical Atlantic several hundred miles southeast of the Cabo 
Verde Islands continues to produce a large area of disorganized 
showers and thunderstorms. Upper-level winds are conducive for 
gradual development, and a tropical depression is likely to form 
in a day or two while the disturbance moves westward to west- 
northwestward at 10-15 kt over the far eastern tropical Atlantic.
This system has a high chance of development during the next 48 
hours. Please refer to the latest NHC Tropical Weather Outlook at 
www.hurricanes.gov for more details.

A well-defined low pressure area associated with the remnants 
of Peter is located a few hundred miles east of Bermuda. The shower 
and thunderstorm activity associated with this system has become 
less organized since early Monday.  Although strong upper-level 
winds are likely to prevent significant development, this system 
could still become a short-lived tropical depression later today or 
tonight while it moves northeastward at about 10 mph.  By Wednesday, 
however, conditions are expected to become unfavorable for further 
development. This system has a medium chance of development in the
next 48 hours. Please refer to the latest NHC Tropical Weather 
Outlook at www.hurricanes.gov for more details.

...TROPICAL WAVES...

Please see the Special Features section for information on the
tropical wave along 17W.

An Atlantic tropical wave has its axis along 35W, south of 17N 
and it is moving W at 10-15 kt. The convection near the tropical 
wave is likely associated with the broad low pressure discussed in
the Special Features section. The northern portion of the wave is
devoid of deep convection due to the dry Saharan air N of 13N.

Another Atlantic tropical wave has its axis along 45W, south of
16N and it is moving W near 10 kt. A few showers are noted where 
the wave interacts with the nearby monsoon trough and ITCZ. The 
wave is devoid of deep convection due to the dry Saharan air N of 
9N.

A central Caribbean tropical wave has its axis along 77W, south 
of 19N and it is moving W near 10 kt. The wave is embedded in a
dry environment, suppressing the development of showers and
thunderstorms.

...MONSOON TROUGH/ITCZ...

A monsoon trough axis enters the Atlantic through the coast of 
Senegal near 15N17W to 08N22W to a 1010 mb low near 08N33W to 
05N39W. The ITCZ extends from 05N39W to 05N44W, then begins W of a
tropical wave near 05N45W to 06N53W. Aside from convection as 
described above under Special Features, scattered moderate 
convection is within 100 nm N of the ITCZ between 40W to 54W.

...GULF OF MEXICO...

A weak surface trough is located about 60 nm offshore of Texas 
and SW Louisiana, paralleling the coastline. Showers and
thunderstorms are within 50 nm of the trough. Isolated 
thunderstorms are also noted in the eastern Gulf and in the Bay 
of Campeche. The rest of the Gulf is dominated by a weak ridge 
positioned over the SE United States. Moderate to fresh 
anticyclonic winds are found in the Florida Straits, in the E Bay 
of Campeche and NW Gulf, while gentle to moderate breezes are 
noted elsewhere in the basin. Seas of 3-4 ft are occurring in the 
Florida Straits, while 1-3 ft are present elsewhere in the Gulf.

For the forecast, the trough continues to extend off the coast 
from southwest Louisiana to south Texas. It will drift westward 
toward the Texas coast this morning. High pressure will persist 
across the eastern and central Gulf through mid week. A weak cold 
front will move into the eastern Gulf toward the end of the week
and exit the area during the weekend. Moderate to locally fresh 
winds are expected across most of the Gulf on Fri. 

...CARIBBEAN SEA...

Numerous strong convection is noted in the SW Caribbean, being
enhanced by the eastern Pacific monsoon trough, S of 12N between
76W to 82W. A surface trough extends south of Cuba and west of 
Jamaica from 21N79W to 17N79W. Scattered moderate convection is 
noted from 15N to 20N between 76W and 80W. Scattered thunderstorms
are also noted south of Hispaniola and west of the Windward 
Islands. A weak pressure gradient across the Caribbean results in 
moderate to locally fresh trades, with the strongest winds found 
within 100 nm of N Colombia and NW Venezuela based on overnight 
scatterometer satellite pass. Seas of 3-5 ft are present in the 
central and SW Caribbean, while 1-3 ft are occurring in the E 
Caribbean and 1-2 ft elsewhere.

For the forecast, Hurricane Sam was near 17.2N 53.9W 953 mb at 5 
AM EDT moving NW at 8 kt. Maximum sustained winds 115 kt gusts 140
kt. Sam will move to 17.9N 54.7W this afternoon, 18.8N 55.9W Wed 
morning, 19.9N 57.4W Wed afternoon, 21.3N 59.0W Thu morning, 23.2N
60.5W Thu afternoon, and 25.6N 61.5W Fri morning. Sam will change
little in intensity as it moves north of the area early Sat. 
Meanwhile, moderate trades will continue over much of the 
Caribbean today. Gentle trades will then prevail over the 
Caribbean through Fri. Swells generated by Sam are forecast to 
continue off the Leeward Islands through the middle of the week.

...ATLANTIC OCEAN...

Please read the Special Features section above for details on 
Hurricane Sam and the disturbances in the deep Tropics.

The Cumbre Vieja volcano on the island of La Palma in the Canary 
Islands has been erupting since 19/1410 UTC. Volcanic ashes
associated with lava fountains are observed on webcams reaching
3,500 meters. Marine and aviation interests should monitor this 
ongoing situation by reading Volcanic Ash Advisory issued by 
Meteo- France at http://vaac.meteo.fr/volcanoes/la-palma/. The 
next advisory will be issued no later than 28/1500 UTC.

A stationary front extends from 31N66W to 25N76W. A trough extends
from the remnants of Peter near 33N58W to 25N71W. Scattered
moderate convection is noted across this region of the Atlantic,
from 20N to 29N between 57W and 80W, particularly near the two
boundaries. Gentle winds prevail with seas to 4 ft. 

In the eastern Atlantic, a surface trough extends from 30N30W to
20N38W. Scattered moderate to isolated strong convection is along
this feature from 20N to 31N between 29W to 38W. A 1016 mb low 
pressure, which is the remnants of Odette, was located near 
30N44W with a trough extending along the low from 31N43W to 
26N47W. The system is devoid of deep convection; however overnight
satellite- derived wind data indicated that fresh winds were 
within 120 nm NE of the center. Overnight scatterometer data also 
show fresh to strong N-NE winds N of 19N and E of 25W, including 
the waters surrounding the Canary Islands, with the strongest 
winds occurring within 100 nm of the coast of Western Sahara. Seas
in the area of 6-10 ft. Elsewhere in the basin outside of the 
influence of Hurricane Sam, winds are moderate or weaker and seas 
are 4-8 ft.

For the forecast W of 50W, the aforementioned stationary front 
extends from 31N65W to the northern Bahamas and is expected to 
dissipate this morning. Light to gentle breezes are expected to 
prevail with slight seas through Thu west of 65W. Meanwhile, 
Hurricane Sam was near 17.2N 53.9W 953 mb at 5 AM EDT moving NW at
8 kt. Maximum sustained winds 115 kt gusts 140 kt. Sam will 
change little in intensity as it moves north of the area by early 
Sat, staying east of Bermuda. At a minimum, expect rough seas in 
the outer swell from Sam from mid to late week, reaching as far 
west as 70W by Thu. 

$$
AReinhart