AXNT20 KNHC 232312
Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0005 UTC Fri Sep 24 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
Tropical Storm Sam is centered near 11.1N 39.7W at 2100 UTC or
1420 nm ESE of the Northern Leeward Islands moving W at 14 kt.
Estimated minimum central pressure is 1000 mb. Maximum sustained
wind speed is 50 kt with gusts to 60 kt. Satellite imagery
depicts a system that is becoming better organized. Numerous
moderate to strong convection is noted within about 50 nm of the
center. Scattered moderate to strong convection is elsewhere in
bands within 240 nm N and 120 nm S semicircles. Peak seas are up
to 15 ft within 90 nm of the center in the NE quadrant and within
60 nm of the center in the NW quadrant. Sam is forecast to move
WNW for the next couple of days and intensify, becoming a
hurricane on Fri and be near major hurricane intensity by the end
of the weekend. Please, read the read the latest HIGH SEAS
FORECAST issued by the National Hurricane Center at website-
https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest Peter
NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov
for more details.
A gale-force, non-tropical low pressure system, the remnants of
Odette, is located near 44N42W, or a little more than 550 nm
west-northwest of the westernmost Azores. While showers and
thunderstorms remain limited near the low, only a small increase
in this activity could result in the formation of a subtropical or
tropical cyclone while it moves generally southeastward over
marginally warmer waters during the next day or so. Strong upper-
level winds are expected to develop over the system beginning
tomorrow, which should then limit further development. Additional
information on this system, including gale warnings, can be found
in High Seas Forecasts issued by the Ocean Prediction Center
ocean.weather.gov. Also see the latest Tropical Weather Outlook at
www.hurricanes.gov for more details.
A far eastern Atlantic tropical wave has its axis just east of
the Cabo Verde Islands near 23W from 05N to 20N, moving westward
at 10 kt. Scattered moderate isolated strong convection is seen
from 05N to 12N between 16W and 27W.
A central Atlantic tropical wave has its axis along 54W from 05N
to 21N, moving westward at 10-15 kt. Scattered moderate convection
is noted from 11N to 15N between 54W and 57W.
The monsoon trough axis passes through the the Senegalese coast
near 15N17W to 08N22W to 08N30W. A segment of the ITCZ extends
from 08N40W to 06N47W. Aside from convection associated to the
tropical waves and Sam described above, scattered moderate
isolated strong convection is from 03N to 07.5N between 26N and
GULF OF MEXICO...
An early season cold front is moving slowly across the Gulf,
extending from near Sarasota, Florida to Veracruz, Mexico. Late
morning ASCAT data passes along with current buoy observations
indicate fresh to locally strong north to northeast winds behind
the front. Moderate to fresh northwest winds are are along and
just offshore the coast of Mexico from Veracruz to Tampico. Recent
altimeter satellite data along with current buoy observations are
showing seas in the range of 4-7 ft behind the front, except to 9
ft offshore of Veracruz. Generally, light to gentle breezes and
slight seas are noted south of the front.
Scattered moderate isolated strong convection is along and within
about 90 nm north of the front, west of 83W. A drier and stable
air mass under high pressure is following in behind the front.
The cold front will stall tonight, then dissipate Sat. Fresh to
strong winds will follow the front into tonight, including along
the coast of Veracruz where seas will be around 8 ft. Looking
ahead, winds and seas will diminish across basin from Sat and into
early next week as high pressure builds over the northern Gulf.
A sharp upper-level trough extends from the vicinity of the
southeastern Bahamas to across eastern Cuba and to the
southwestern Caribbean. This trough is acting on an already
very moist and unstable environment resulting in enhanced
scattered moderate to strong convection over the far south-
central and southwestern Caribbean from along the coast of
Colombia and Panama to 15N and between 73W-81W. A weakened
subtropical ridge north of the area continues to support a pattern
of below average winds across the basin. Moderate trade winds are
noted over the southeast Caribbean, with generally light to
gentle trade winds elsewhere. Seas are relatively low, in the 2-3
ft range, except for slightly higher seas of 3-4 ft across the
waters north of the A-B-C Islands.
For the forecast, Tropical Storm Sam near 10.9N 38.1W 1003 mb at
1500 UTC, moving W at 14 kt. Maximum sustained winds are 45 kt
with gusts to 55 kt. Sam will continue to intensify as it moves
across the Atlantic, becoming a hurricane near 12N45W by Fri
evening, and reaching 55W east of the Leeward Islands by Mon
night. Meanwhile, moderate trade winds will persist over much of
the Caribbean into early next week, becoming fresh over the south-
central Caribbean starting Fri night as high pressure builds east
of the Bahamas.
Please read the Special Features section above for details on
newly formed Tropical Storm Sam.
The Cumbre Vieja volcano on the island of La Palma in the Canary
Islands has been erupting since 19/1410 UTC. A significant ash
emission is ongoing 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 issue no later than 23/2300 UTC.
A stationary front extends from near 31N45W to 27N68W. Morning
ASCAT data depicted moderate to mainly fresh east to southeast
winds north of the stationary front between 56W-59W. A cold front
has moved off the southeastern United States coast and extends
from 31N78W to inland central Florida. A pre-frontal trough
extends just SE of the front to inland South Florida. Satellite
imagery shows scattered showers and thunderstorms north of 26N
and between 73W-79W. Broken to overcast multilayered clouds with
embedded areas of rain along with scattered and isolated
thunderstorms are seen north of 25N between 57W-64W. The 1009 mb
remnant low of Peter is near 24N67W. A trough extends northeast
from the low to 26N64W, and southwest from the low to the north-
central coast of Hispaniola. An expanding area of scattered
moderate to isolated strong convection is well removed to the east
of the low from 22N to the stationary front and between 60W- 65W.
Similar activity is also from 19N to 22N between 63W-67W. Morning
ASCAT data showed fresh to strong southerly winds with this
convective activity. Altimeter data indicates seas up to 7 ft
northeast and east of the low from 22N to 28N between 62W-67W.
Seas may be slighter higher in the strong convection.
The post-tropical cyclone remnant 1010 mb low of former tropical
cyclone Rose is near 27N42W. A trough to its southwest extends
from 23N45W to 19N48W. Morning altimeter pass has seas up to 11
ft within about 60 nm in the northwest quadrant of this low. This
attributed to a large area of northerly swell that is producing
seas of 8-12 ft seas north of 22N between 35W-60W. Fresh east to
southeast winds are over the eastern semicircle of the low. The
low will gradually dissipate through Sat. Aside from the features
and related winds and seas already mentioned in this discussion,
moderate to occasionally fresh trade winds are noted across the
basin along with 4 to 6 ft seas in open waters.
For the forecast west of 65W, a cold front extending from 31N78W
to Cape Canaveral, Florida will stall from 31N77W to near Fort
Pierce, Florida by tonight, then dissipate through early Sun just
before a second weak front possibly moves into the region late
Sun. Farther east, Tropical Storm Sam will intensify to a
hurricane by Fri afternoon near 12N44W and to a major hurricane
Sat afternoon near 13N47W. Sam will reach near 15N 52.5W Mon and
be near 17.5N 55.5W Tue.