AXNT20 KNHC 260501
Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0605 UTC Sun Sep 26 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 0000 UTC surface analysis and satellite imagery through
Hurricane Sam continues to intensify well east of the Lesser
Antilles. The hurricane is centered near 13.5N 49.0W at 0300 UTC,
or 860 nm ESE of the Northern Leeward Islands, moving WNW at 7
kt. Estimated minimum central pressure is 943 mb. Maximum
sustained wind speed is 125 kt with gusts to 150 kt. Peak seas
are estimated near 30 ft and are anticipated to reach near 36 ft
by Monday. Sam has an exceptionally well-defined eye with very
strong convection surrounding it. Satellite imagery shows
numerous moderate to strong convection within 90 nm of Sam's
center. Sam is moving toward the west-northwest and this general
motion is forecast to continue through Sunday. A turn toward the
northwest is expected on Monday. Fluctuations in intensity are
likely into early next week as Sam undergoes structural changes.
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://hurricanes.gov
for more details.
An Atlantic tropical wave has its axis along 22W, south of 17N,
and it is moving W around 10 kt. A few showers are noted near the
southern portion of the wave axis. The northern portion is
embedded in a dry Saharan airmass, suppressing the development of
showers and thunderstorms.
Another Atlantic tropical wave has its axis along 34W, south of
17N, and it is moving W around 10 kt. Widely scattered moderate
convection is observed from 04N and 12N and between 28W and 38W.
Satellite imagery show that the northern part of the wave remains
embedded in dry Saharan air, inhibiting the development of shower
and thunderstorm activity to the north of 11N.
A Caribbean tropical wave has its axis along 68W, south of 20N,
and it is moving W around 10-15 kt. No significant deep
convection is noted over water in association with this wave.
The monsoon trough passes through coast of Guinea-Bissau near
12N16W to 08N25W and to 07N36W. The ITCZ extends from 07N37W to
09N45W. Aside from convection associated to the tropical waves
and Sam described above, scattered moderate to isolated strong
convection is seen within 200 nm of the monsoon trough and ITCZ
between 24W and 46W.
GULF OF MEXICO...
The weak stationary front draped across the Gulf of Mexico has
weakened into a surface trough that extends from the NE Gulf near
the Big Bend area of Florida to south-central Gulf near 22N93W. A
few showers are noted near the trough axis. Scattered moderate
convection is also present in the Bay of Campeche, E of 94W. Dry
air dominates the rest of the basin, allowing for fairly tranquil
weather conditions. A weak pressure gradient across the Gulf
results in moderate to locally fresh E-NE winds, with the
strongest winds occurring in the central Gulf, north of the
surface trough. Seas W of 88W are 3-5 ft, with the highest seas
occurring in the central Gulf. Seas E of 88W are 1-3 ft.
For the forecast, a surface trough extends across the basin from
30N83W to 23N93W with scattered showers. Moderate to locally fresh
winds prevail north of the trough. Winds and seas will diminish
across the basin through Mon as high pressure builds over the
Refer to the section above for details on the tropical wave
moving across the easter Caribbean.
The eastern extension of the E Pacific monsoon trough and abundant
moisture results in scattered moderate to isolated strong
convection within 130 nm of the coast of Nicaragua, Costa Rica,
Panama and NW Colombia. A few showers are also noted in the Gulf
of Honduras. The rest of the Caribbean is dominated by a fairly dry
A modest north-south pressure gradient persists in the south-central
Caribbean between a broad Colombian Low and weak ridging north of
the basin. Recent scatterometer satellite data indicate that
fresh to strong trades are occurring within 200 nm of the north
coast of Colombia and 70 nm of the coast of NW Venezuela,
encompassing the Gulf of Venezuela and the waters surrounding the
ABC islands. Trades elsewhere in the Caribbean are gentle to
moderate. Seas are 4-6 ft over the south- central Caribbean and
2-4 ft elsewhere.
Hurricane Sam near 13.5N 49.0W 943 mb at 11 PM EDT
moving WNW at 7 kt. Maximum sustained winds 125 kt gusts 150 kt.
Sam will move to 14.0N 49.9W Sun morning, 14.7N 51.0W Sun
evening, 15.4N 52.1W Mon morning, 16.3N 53.2W Mon evening, 17.1N
54.3W Tue morning, and 18.0N 55.6W Tue evening. Sam will change
little in intensity as it moves to 20.1N 58.5W by late Wed.
Meanwhile, moderate trade winds will persist over much of the
Caribbean into early next week. Fresh winds will prevail over the
south-central Caribbean as high pressure builds east of the
Bahamas through Mon.
Please read the sections above for details on Hurricane Sam and
tropical waves moving across the basin.
The Cumbre Vieja volcano on the island of La Palma in the Canary
Islands has been erupting since 19/1410 UTC. Significant
volcanic ash mainly in the vicinity of the volcano. Marine and
aviation interests should monitor this on-going 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 26/0900 UTC.
The weakening stationary front that stretched from the offshore
waters of the SE United States to the Treasure Coast of Florida
has weakened into a surface trough that is currently analyzed
between 31N72W to 24N80W. A few showers and isolated thunderstorms
are observed on infrared satellite imagery near the trough axis,
with the strongest convection affecting parts of the NW Bahamas.
A 1012 mb low pressure - the remnants of Peter - is located near
27N63W and a surface trough extends across the low pressure from
31N61W to 22N66W. A large area of showers and thunderstorms is
found east of the trough axis from 24N to 30N and between 58W and
63W. A recent scatterometer satellite pass show fresh southerly
winds associated with the convection.
Also, a 1011 mb low pressure - the remnants of Rose - is located
near 30N33W and a trough extends from the low pressure center to
25N42W to 30N52W. A band of moderate convection is noted well east
and southeast of the low pressure and a few showers are seen near
the trough axis. Satellite-derived wind data show fresh to strong
southerly winds in the area affected by the convection, mainly N
of 23N and between 29W and 34W. Low-level convergence is
producing an area of moderate to strong convection from 21N to 23N
and between 35W and 40W. Elsewhere in the tropical N Atlantic
(aside from near Hurricane Sam), fairly tranquil weather
conditions and moderate or weaker winds prevail. Seas of 4-7 ft
are prevalent across the basin, aside from near Hurricane Sam.
A surface trough extends from 31N72W to 25N79W with
scattered showers. Farther east, Hurricane Sam near 13.5N 49.0W
943 mb at 11 PM EDT moving WNW at 7 kt. Maximum sustained winds
125 kt gusts 150 kt. Sam will move to 14.0N 49.9W Sun morning,
14.7N 51.0W Sun evening, 15.4N 52.1W Mon morning, 16.3N 53.2W Mon
evening, 17.1N 54.3W Tue morning, and 18.0N 55.6W Tue evening.
Sam will change little in intensity as it moves to 20.1N 58.5W by