000 AXNT20 KNHC 250507 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 0605 UTC Sat Sep 25 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 0505 UTC. ...SPECIAL FEATURES... Hurricane Sam continues to gain strength over the central Atlantic. It is centered near 12.4N 45.9W at 0300 UTC, or about 1055 nm ESE of the Northern Leeward Islands, moving WNW at 12 kt. Estimated minimum central pressure is 982 mb. Maximum sustained wind speed is 85 kt with gusts to 100 kt. The appearance continues to improve as an eye becomes better defined on infrared satellite imagery. Numerous moderate to strong convection within about 40 nm of the center. Scattered moderate to strong convection is elsewhere in bands within 130 nm E and 80 nm E semicircles, making Sam a very compact hurricane. Peak seas near the center are estimated near 25 ft and expected to reach 30 ft by Sunday morning. A motion toward the west or west-northwest with a decrease in forward speed is expected over the weekend. A turn toward the northwest is forecast on Monday. Additional strengthening is forecast, and Sam is expected to become a major hurricane on Saturday. Swell associated with Sam is expected to reach the Lesser Antilles Sunday evening. Please read the latest HIGH SEAS FORECAST issued by the National Hurricane Center at https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest NHC Forecast/Advisory and Public Advisory on Sam at www.hurricanes.gov for more details. Subtropical Storm Teresa is centered near 34.3N 65.4W at 0300 UTC, moving WNW at 9 kt. Estimated minimum central pressure is 1008 mb. Maximum sustained wind speed is 40 kt with gusts to 50 kt. The center of Teresa is devoid of deep convection. Scattered moderate isolated strong convection is seen well removed from the center, and occurring within 200 nm across the N and 400 nm across the NE quadrants. The storm is moving toward the west-northwest and a turn toward the north and northeast is expected during the next day or two. Little change in strength is forecast during the next 36 hours. Teresa is expected to be short-lived and should dissipate in about two days. Please see the latest High Seas Forecasts issued by the Ocean Prediction Center at https://ocean.weather.gov/shtml/NFDHSFAT1.php and the latest NHC Forecast/Advisory and Public Advisory on Teresa at www.hurricanes.gov for more details. ...TROPICAL WAVES... An Atlantic tropical wave has its axis along 29W, south of 19N, and it is moving W at 10-15 kt. A few showers are noted near the southern portion of the wave. Satellite imagery show that the northern part of the wave remains embedded in dry Saharan air, inhibiting the development of shower and thunderstorm activity. A tropical wave extends across the Lesser Antilles and into E Venezuela. It has its axis near 61W, south of 20N, and it is moving W near 15 kt. A few showers are observed near the wave axis. ...MONSOON TROUGH/ITCZ... The monsoon trough axis passes through coast of Senegal near 13N16W to 08N25W and to 06N32W. A segment of the ITCZ extends from 06N33W to 07N40W and another segment continues from 06N48W to 06N53W. Aside from convection associated to the tropical waves and Sam described above, isolated moderate convection is noted from 04N to 10N and between 30W to 45W. Another area of scattered moderate convection is seen south of the Cabo Verde Islands from 10N to 12N and between 20W to 25W. GULF OF MEXICO... A stationary front meanders across the southern Gulf of Mexico from SW Florida to Veracruz. A few showers are noted on infrared satellite imagery along the frontal boundary. The air mass behind the front is quite dry, allowing fairly tranquil weather conditions across the northern and western Gulf, from Florida to northern Veracruz. Satellite-derived wind data and surface observations indicate that moderate to locally fresh winds dominate the basin, with the strongest winds occurring in the central Gulf. Seas in the central and SW Gulf are 3-5 ft, and 1-3 ft elsewhere. For the forecast, a stationary front extends across the southern Gulf from Naples, Florida to Veracruz, Mexico. This boundary will dissipate by late Sat. Moderate to fresh winds prevail north of the front. Winds and seas will diminish across basin from Sat night and into early next week as high pressure builds over the northern Gulf. CARIBBEAN SEA... Scattered moderate convection is noted within 100 nm of the coast of NE Honduras, Nicaragua and northern Costa Rica. A surface trough extends from the Yucatan Channel to northern Honduras, but only a few shallow showers are near this feature. The surface trough is quite evident in a recent scatterometer satellite pass, showing broad troughiness over the Gulf of Honduras. A few showers are also observed in the E Caribbean, near the Lesser Antilles, due to moisture associated with a tropical wave entering the region. The remainder of the Caribbean enjoys fairly tranquil weather conditions thanks to a drier environment. Satellite- derived wind data indicate fresh to strong trades in the south- central Caribbean, mainly within 170 nm of the northern coast of Colombia. Gentle to moderate trades are found in the rest of the basin. Seas of 3-5 ft are present in the central and eastern Caribbean, with the highest seas occurring in the south-central portion of the basin. Elsewhere, seas are 1-3 ft. For the forecast, Hurricane Sam near 12.4N 45.9W 982 mb at 11 PM EDT moving WNW at 12 kt. Maximum sustained winds 85 kt gusts 105 kt. Sam will move to 12.7N 47.4W Sat morning, 13.1N 48.8W Sat evening, 13.5N 50.0W Sun morning, 14.1N 51.2W Sun evening, 14.8N 52.4W Mon morning, and 15.7N 53.5W Mon evening. Sam will change little in intensity as it moves to 17.4N 55.8W by late 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. 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. The height of the ash plume cloud is difficult to estimate due to cloud cover. 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 25/0900 UTC. A cold front just east of the United States continues its eastward progression across the NW Atlantic. The southern portion of this front transitions to a stationary front from 31N75W to the Treasure Coast of Florida near 27N80W. A pre-frontal surface tough is analyzed from 31N74W to SW Florida. Scattered moderate to isolated strong convection is observed on infrared satellite imagery from 23N to 30N and W of 73W. A recent scatterometer satellite pass depicted fresh to strong southerly winds in the central Bahamas in association with the convection affecting the area. Another surface trough extends from 30N61W to the 1011 mb remnant low of Peter near 24N65W to 20N66W. The interaction of these features with an upper level trough to the north results in a large area of showers and thunderstorms from 22N to 30N and between 58W and 64W. Satellite-derived wind data show fresh to locally strong winds to the east of the surface trough, likely associated with the convection in the area. Seas W of 60W are 3-6 ft. Farther east, latest scatterometer satellite data indicate that the the remnant low of Rose has weakened into a sharp surface trough, extending from 31N38W to 26N40W. In the vicinity of this feature is a stationary front that stretches from 31N40W to 28N47W. An upper level trough nearby is interacting with these features, inducing a large area of scattered moderate to isolated strong convection N of 27N and between 32W and 40W. Satellite- derived wind data depict fresh to strong southerly winds N of 25N and between 36W and 40W, likely associated with the convection. Two other surface troughs traverse the Atlantic, one stretches from 22N53W to 18N54W and the other one along 30W from 26N to 31N. Neither of these features is producing deep convection. Moderate to fresh northerly winds are found off the coast of Mauritania, mainly east of 20W. E of 60W and N of 20N, seas are 5-8 ft, with the highest seas found off the coast of Mauritania. In the rest of the basin, moderate to fresh trade winds are noted along with 4 to 6 ft seas. For the forecast, the front extending from 31N75W to West Palm Beach, Florida, will remain stationary and weaken through early Sun. Then, reinforcing moderate N winds will push the front eastward as a weak cold front, reaching from 31N69W to 27N74W by Mon morning. The front will stall and dissipate Tue. Farther east, Hurricane Sam is near 12.4N 45.9W 982 mb at 11 PM EDT, moving WNW at 12 kt. Maximum sustained winds 85 kt gusts 105 kt. Sam will strengthen to a major hurricane on Sat near 12N47W and move to near 13.5N50.0W Sun morning, 14.1N 51.2W Sun evening, 14.8N52.4W Mon morning, and 15.7N53.5W Mon evening. Sam will change little in intensity as it moves to 17.4N55.8W by late Tue. $$ DELGADO