677 AXNT20 KNHC 280540 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 0605 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 0000 UTC surface analysis and satellite imagery through 0535 UTC. ...SPECIAL FEATURES... Hurricane Sam is centered near 16.8N 53.2W at 28/0300 UTC or 575 nm E of the Northern Leeward Islands. It is moving NW at 8 kt. Estimated minimum central pressure is 956 mb. Maximum sustained wind speed is 105 kt with gusts to 130 kt. Seas near the center are currently around 27 ft and are forecast to increase to near 34 ft by Wednesday. Satellite imagery continues to show a well-defined eye, although much larger than it was a couple of days ago. Numerous moderate to scattered strong convection is within 60 nm of the center in the N and within 60 nm of the center in the S quadrant. Scattered moderate convection is within 200 nm of the center in the NE quadrant and within 90 nm in the SW quadrant. The current NW motion is expected to continue for the next few days, with an increase in forward speed beginning on Thursday. A turn to the north is expected by Friday. On the forecast track, Sam will pass well to the northeast of the northern Leeward Islands Wednesday and Thursday. The hurricane could strengthen some overnight, and Sam is anticipated to be a category 3 or 4 hurricane for the next several days. Swells generated by Sam will impact the Lesser Antilles for the next several days. Swells are expected to reach Bermuda and the Bahamas mid-to-late week, 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, however, 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 scattered moderate to isolated strong convection from 03N to 13N and between 25W and 35W. 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 5 to 10 mph 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 just offshore the west coast of Africa along 17W, south of 17N and to a 1010 mb low pressure near 07N17W. This system is producing a large area of disorganized scattered moderate to isolated strong convection from 03N to 12N and between 16W and 25W. 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 to 15 mph 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. ...TROPICAL WAVES... Please see the Special Features section for information on the tropical wave along 17W. An Atlantic tropical wave has its axis along 33W, 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 43W, south of 17N 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 76W, 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 14N17W to 07N22W to 09N28W to a 1008 mb low pressure near 08N32W and to 06N40W. An ITCZ segment then extends from 07N44W to 07N53W. Aside from convection as described above under Special Features, scattered moderate convection is within 100 nm N of the ITCZ between 42W to 50W. ...GULF OF MEXICO... The only feature of interest in the Gulf of Mexico remains a weak surface trough that is located about 60 nm offshore of Texas and SW Louisiana, paralleling the coastline. A few showers are observed near the trough axis. 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 will drift westward toward the Texas coast through tonight. 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, before stalling and dissipating over the southeast Gulf by the weekend. Moderate to locally fresh winds are expected across most of the Gulf on Fri. ...CARIBBEAN SEA... Divergence aloft is enhancing the development of showers and thunderstorms across the north-central Caribbean Sea, especially in the islands in the region. At this hour, most of the storm activity is decreasing, but there are still some showers and isolated thunderstorms in E Cuba and Hispaniola and surrounding waters. Scattered moderate convection is also seen in the SW Caribbean, mainly between the island of San Andres and Panama. The rest of the Caribbean Sea is dominated by dry weather conditions. 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 a recent 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 16.8N 53.2W 956 mb at 11 PM EDT moving NW at 8 kt. Maximum sustained winds 105 kt gusts 130 kt. Sam will move to 17.5N 54.0W Tue morning, 18.4N 55.1W Tue evening, 19.3N 56.4W Wed morning, 20.6N 58.0W Wed evening, 22.2N 59.7W Thu morning, and 24.3N 61.0W Thu evening. Sam will change little in intensity as it moves north of the area late Fri. Meanwhile, moderate trades will continue over much of the Caribbean through Tue. 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 28/0900 UTC. A cold front enters the W tropical Atlantic near 31N64W and transitions into a stationary front that stretches to the NW Bahamas near 25N75W. Scattered moderate convection is observed near the frontal boundary, mainly from 25N to 28N and between 67W and 76W. A surface trough extends from a 1012 mb low pressure, the remnants of Peter, near 32N58W to 24N66W. A few showers and isolated thunderstorms is noted within 60 nm of the trough axis, especially near the southern portion. Seas W of 60W are 3-5 ft. Another feature of interest is a surface trough that extends from 31N28W to 20N36W. Numerous moderate showers and isolated strong thunderstorms are present within 60 nm of the trough axis. A 1015 mb low pressure, the remnants of Odette, are located near 30N43W and although the system is devoid of deep convection, satellite- derived wind data indicate that it is producing fresh breezes within 120 nm NE of the center. Recent 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 is expected to dissipate tonight. Light to gentle breezes are expected to prevail with slight seas into mid week west of 65W. Meanwhile, Hurricane Sam was near 16.8N 53.2W 956 mb at 11 PM EDT moving NW at 8 kt. Maximum sustained winds 105 kt gusts 130 kt. Sam will move to 17.5N 54.0W Tue morning, 18.4N 55.1W Tue evening, 19.3N 56.4W Wed morning, 20.6N 58.0W Wed evening, 22.2N 59.7W Thu morning, and 24.3N 61.0W Thu evening. Sam will change little in intensity as it moves north of the area, staying east of Bermuda late Fri. At a minimum, expect rough seas in the outer swell from Sam from mid to late week, reaching as far west as 70W by late Thu. $$ DELGADO