000 AXNT20 KNHC 280005 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 0005 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 1800 UTC surface analysis and satellite imagery through 2345 UTC. ...SPECIAL FEATURES... Major Hurricane Sam is centered near 16.3N 52.7W at 27/2100 UTC or 610 nm E of the Northern Leeward Islands. It is moving NW at 8 kt. Estimated minimum central pressure is 957 mb. Maximum sustained wind speed is 105 kt with gusts to 130 kt. Seas are peaking to a range of 29-33 ft within 50 nm the center, and ranging between 15 and 25 ft farther out to 100 nm in a northern semicircle nd out to 60 nm in a southern semicircle. Satellite imagery shows that an eye feature has become visible once again. Numerous moderate to scattered strong convection is within 90 nm of the center in the NE and within 60 nm of the center in the SE quadrant. Scattered moderate convection is within 120 nm of the center in the SW and within 150 nm in the NW quadrant. The present NW motion is forecast to continue for the next few days, with an increase in forward speed beginning on Thu. A turn to the north is expected by Fri. On the forecast track, Sam will pass well to the northeast of the northern Leeward Islands Wed and Thu. Some strengthening is expected through tonight. Thereafter, fluctuations in intensity are possible through Thu. 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. Although scattered moderate convection to northeast of the low center from 32N to 33N between 56W-58W is currently disorganized, environmental conditions are expected to remain marginally conducive for a short-lived tropical depression to form tonight or Tue while the system moves northeastward at about 10 mph. By Wed, 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 04N to 11N between 20W-30W. Environmental conditions are conducive for further development of this disturbance, and a tropical depression is likely to form during the next day or two while the system moves westward to west-northwestward near 8 kt 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 extends from 16N17W to a 1010 low near 07N17W and to 04N12N. This system is producing a large area of disorganized scattered moderate to isolated strong convection from 04N to 08N between 15W-20W. Upper-level winds are conducive for gradual development, and a tropical depression is likely to form in a couple of days while the system moves westward to west- northwestward at 8 to 13 kt 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 above for information on a far eastern Atlantic Special Feature tropical wave along 16W/17W. An eastern Atlantic tropical wave has its axis along 32W from 04N to 17N, moving westward near 15 kt. Scattered moderate to isolated strong convection is within 180 nm east of the wave from 10N to 11N and within 120 nm east of the wave from 04N to 07N. Scattered moderate convection is within 180 nm west of the wave from 09N to 11N. A central Atlantic tropical wave has its axis along 42W from 03N to 16N. It is moving westward at 10-15 kt. Isolated moderate convection is within 120 nm west of the wave from 08N to 09N and within 60 nm east of the wave from 08N to 09N. A central Caribbean tropical wave has its axis along 75W south of 19N to inland northwest Colombia. It is moving westward near 10 kt. No significant conveciton is noted with this wave over the Caribbean. Scattered moderate convection is within 30 nm of the wave axis over Colombia from 08N to 10N. ...MONSOON TROUGH/ITCZ... A monsoon trough axis enters the Atlantic through the coast of Senegal near 14N17W to 08N24W and to 08N40W. An ITCZ segment begins at 08N43W to 07N50W. Aside from convection as described above under Special Features, scattered moderate convection is within 60 nm north of the ITCZ between 46W-50W. ...GULF OF MEXICO... A surface trough remains in the NW Gulf just off the Texas- Louisiana coasts. This feature is producing scattered showers and isolated thunderstorms over the NW and north-central Gulf waters. Otherwise, a broad surface ridge extending southwestward from the mid- Atlantic US States to central Mexico is dominating much of the Gulf with light to gentle winds and seas of 2 to 3 ft. 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 Thu night through Fri, before stalling and dissipating over the southeast Gulf by Sat. ...CARIBBEAN SEA... An upper-level low over the eastern Caribbean near 14N66W is producing isolated showers and thunderstorms over the southeast part of the basin. Moderate to fresh northeast to east trades along with seas of 4 to 6 ft are evident across the central and south- central sections of the basin. Light to gentle trades and seas of 2 to 3 ft prevail for the rest of the basin. The eastern end of the E Pacific monsoon trough is triggering numerous moderate to strong convection over the far southwest part of the sea south of 13N and west of 79W. The southern part of an upper-level trough over the northwest Caribbean is aiding this convection. Similar convection is over Panama and southern Costa Rica. Scattered moderate to isolated strong convection is over the interior sections of the Dominican Republic. For the forecast, Hurricane Sam was near 16.3N 52.7W 957 mb at 2100 UTC, moving NW at 8 kt. Maximum sustained winds are 105 kt, with gusts to 130 kt. Sam will move to 17.0N 53.5W Tue morning, 17.8N 54.6W Tue afternoon, 18.8N 55.8W Wed morning, 19.8N 57.3W Wed afternoon, 21.2N 59.0W Thu morning, and 22.9N 60.5W Thu afternoon. Sam will change little in intensity as it continues to move north of the area through Fri. Meanwhile, moderate trades will continue over much of the Caribbean through Tue. Fresh trades over the south- central Caribbean will diminish to gentle to moderate speeds today. 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. The Cumbre Vieja volcano on the island of La Palma in the Canary Islands has been erupting since 19/1410 UTC. Significant volcanic ash is mainly in the vicinity of the volcano below 6000 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 issued no later than 28/0300 UTC. A cold front extends from 31N65W to 27N71W and to the NW Bahamas. Scattered showers and isolated thunderstorms are found up to 100 nm NW, and up to 80 nm SE of this front. A weakening frontal boundary extends southwestward from NW of the Canary Islands across 31N28W through a low pressure near 22N36W then turns westward to 22N46W. Similar conditions exist up to 80 nm on neither side of this boundary N of 22N. A surface trough extends from 25N65W to low pressure, remnants of Peter, near 31N59W 1010 mb. Scattered moderate convection is within 60 nm of 25N65W and within 30 nm east of the trough from 27N-29N. An eastern 1015 mb low is located near 23N36W, with a trough to 21N41W and to 22N46W, and another trough northeast from the low to 29N29W. Scattered moderate convection is within 120 nm of the low in the NE quadrant, and within 30 nm of the trough between 32W-33W. Refer to the Tropical Waves and Monsoon Trough/ITCZ sections for additional convection across the basin. Light to gentle winds and seas at 3 to 5 ft are evident N of 20N between 28W and the 64W. N of 20N, moderate to locally fresh winds and seas of 4 to 7 ft are seen 64W and the Georgia-Florida coast, and also between the NW African coast and 28W, including the Canary Islands. Outside the influence of Hurricane Sam, gentle to moderate trades and seas at 5 to 6 ft are found from 10N to 20N between the African coast and the Less Antilles. Gentle to locally moderate monsoonal winds and seas of 4 to 7 ft prevail for the remainder of the basin. For the forecast W of 45W, the cold front that extends from 31N65W to 27N71W and to the NW Bahamas will stall this evening and dissipate overnight, leaving generally light to gentle breezes and slight seas into mid week west of 65W. Meanwhile, Hurricane Sam was near 16.3N 52.7W 957 mb at 21 UTC, moving NW at 8 kt. Maximum sustained winds are 105 kt, with gusts to 130 kt. Sam will move to 17.0N 53.5W Tue morning, 17.8N 54.6W Tue afternoon, then to northeast of the Leeward Islands near 18.8N 55.8W by early Wed morning. Sam will continue to move northwest to 19.8N 57.3W Wed afternoon, 21.2N 59.0W Thu morning, and 22.9N 60.5W Thu afternoon. Sam will change little in intensity as it moves northward to southeast of Bermuda through 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. $$ Aguirre