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000
AXNT20 KNHC 241204
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 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 0600 UTC surface analysis and satellite imagery through 1145 UTC.


...SPECIAL FEATURES...

Hurricane Sam is centered near 11.5N 42.2W at 24/0900 UTC or 1280 nm ESE of the Northern Leeward Islands moving W at 13 kt. Estimated minimum central pressure is 993 mb. Maximum sustained wind speed is 65 kt with gusts to 80 kt. Satellite imagery depicts numerous moderate to strong convection is from 09N to 16N between 39W and 45W. Peak seas are currently near 20 ft. A decrease in forward speed and a motion toward the west- northwest are expected over the weekend. Rapid intensification is forecast to continue, and Sam is likely to become a major hurricane tonight or early Saturday. Please read the latest NHC Public Advisory at https://www.nhc.noaa.gov/text/MIATCPAT3.shtml and Forecast/ Advisory at https://www.nhc.noaa.gov/text/MIATCMAT3.shtml for more details.

A gale-force, non-tropical low pressure system is centered near 44N41W, or a little more than 525 nm west-northwest of the westernmost Azores. Showers and thunderstorms remain limited near the low, and this system has only a brief window of opportunity to become a subtropical or tropical cyclone while it moves generally south-southeastward over marginally warmer waters. Strong upper- level winds are expected to develop over the system by late today, 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 large area of showers and thunderstorms centered a couple hundred miles east of Bermuda is associated with a formative surface low interacting with an upper-level trough. Additional tropical or subtropical development of this system could occur through early Saturday as it moves generally north- northwestward. After that time, development is not expected due to strong upper-level winds. This system has a medium chance of tropical cyclone development during the next 48 hours. 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.


...TROPICAL WAVES...

An Atlantic tropical wave has its axis along 25W, south of 20N, and it is moving W at 10 kt. Scattered showers are noted within 45 nm on either side of the wave axis mainly south of 13N. The northern part of the wave is embedded in dry Saharan air, inhibiting the development of showers and thunderstorms.

An Atlantic tropical wave has its axis along 56W, south of 20N, and it is moving W at 10-15 kt. Scattered showers are noted within 45 nm on either side of the wave axis mainly south of 14N.


...MONSOON TROUGH/ITCZ...

The monsoon trough passes through coast of Senegal near 14N17W to 06N28W. A segment of the ITCZ extends from 06N28W to 09N37W and another segment continues from 07N47W to 06N55W. Aside from convection associated to the tropical waves and Sam described above, scattered showers prevail along the ITCZ between 28W and 37W.

GULF OF MEXICO...

The main feature of interest in the Gulf of Mexico is frontal boundary that traverses the basin from SW Florida to Veracruz. The front is analyzed as stationary in the southern Gulf waters. A few showers and thunderstorms are noted along the boundary. The airmass behind the front is quite dry, allowing fairly tranquil weather conditions front Texas to Florida in the N Gulf. Recent scatterometer satellite data depicts fresh NE winds behind the frontal boundary in the central Gulf, especially from 25N to 28N and between 85W and 90W. Fresh to locally strong N-NE winds are depicted in the SW Gulf, especially near the coast of Veracruz. Seas behind the front are 4-6 ft and 2-4 ft ahead of the boundary.

For the forecast, the front will dissipate by Sat. Fresh winds prevail within 100 nm north of the front with seas ranging between 4 to 6 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.

CARIBBEAN SEA...

A sharp upper-level trough extends from the vicinity of the southeastern Bahamas to across eastern Cuba and to the southwestern Caribbean. A surface trough is analyzed in the W Caribbean extending along 84W from 17N-22N. This is allowing for the development of afternoon and evening thunderstorms across the western and central Caribbean Sea. Scattered moderate convection is also noted in the SW and south- central Caribbean, especially near the northern coast of Colombia. A recent scatterometer pass indicate fresh trades within 130 nm of the coast of NW Venezuela, including the waters surrounding the ABC islands, while gentle to moderate trades prevail elsewhere. Seas in the central and E Caribbean are 2-4 ft, while 1-2 ft are noted elsewhere.

For the forecast, Hurricane Sam is near 11.5N 42.2W 993 mb at 5 AM EDT moving W at 13 kt. Maximum sustained winds 65 kt gusts 80 kt. Sam will move to 11.7N 44.0W this afternoon, 12.1N 45.9W Sat morning, 12.5N 47.4W Sat afternoon, 12.9N 48.7W Sun morning, 13.4N 50.0W Sun afternoon, and 14.1N 51.1W Mon morning. Sam will change little in intensity as it moves to 15.9N 53.8W by early Tue. Meanwhile, moderate trade winds will persist over much of the Caribbean into early next week, becoming fresh over the south- central Caribbean starting tonight as high pressure builds east of the Bahamas. Fresh to strong winds are forecast in the Gulf of Honduras Sun night.

ATLANTIC OCEAN...

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. A significant ash emission is ongoing in the vicinity of the volcano below 10,000 ft. 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 24/1500 UTC.

A cold front extends from 31N76W to 27N80W. A pre-frontal trough is noted just ahead of the cold front from 28N78W to South Florida. Scattered moderate convection is observed on satellite imagery N of 27N and W of 74W. Recent satellite-derived wind data show fresh to locally strong SE-S winds from 27N to 31N and between 73W and 76W. Seas in this region are ranging between 4-6 ft.

Another area of interest is a sharp surface trough extending from 31N60W to 25N65W and the 1009 mb low near 23N67W. The interaction of these features with an upper-level low near Bermuda is inducing a large area of showers and thunderstorms, especially from N of 20N and between 56W and 64W. Scatterometer wind data indicate fresh to strong cyclonic winds near the northern end of the surface trough, N of 28N. Seas in this region are 5-8 ft, with the highest seas noted near the highest winds.

Farther east, the 1010 mb low is located near 28N43W. Scattered showers and thunderstorms are noted N of 26N between 35W-40W. A stationary front is analyzed from 31N46W to 27N54W with no significant convection. Fresh northerly winds are found off the coast of Mauritania, mainly E of 20W. A large area of northerly swell that is producing 8-11 ft seas N of 22N and between 35W and 60W. Moderate to fresh trade winds are noted elsewhere across the basin along with 4 to 6 ft seas in open waters.

For the forecast west of 65W, the cold front will stall then dissipate through early Sun just before a second weak front possibly moves into the region late Sun. Farther east, Hurricane Sam is centered near 11.5N 42.2W 993 mb at 5 AM EDT, moving W at 13 kt. Maximum sustained winds 65 kt gusts 80 kt. Sam will move to 11.7N 44.0W this afternoon, 12.1N 45.9W Sat morning, 12.5N 47.4W Sat afternoon, 12.9N 48.7W Sun morning, 13.4N 50.0W Sun afternoon, and 14.1N 51.1W Mon morning. Sam will change little in intensity as it moves to 15.9N 53.8W by early Tue.

$$ ERA

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