000 AXNT20 KNHC 271806 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1805 UTC Mon Sep 27 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 1200 UTC surface analysis and satellite imagery through 1530 UTC. ...SPECIAL FEATURES... Major Hurricane Sam is centered near 15.7N 52.1W at 27/1500 UTC or 645 nm ESE of the Northern Leeward Islands, and moving NW at 7 kt. Estimated minimum central pressure is 966 mb. Maximum sustained winds are 110 kt with gusts to 135 kt. Seas are peaking from 28 to 30 ft within 50 nm the center, and ranging between 15 and 25 ft farther out to 100 nm in a northern semicircle; and out to 60 nm in a southern semicircle. Numerous moderate to scattered strong convection is seen near the center from 14N to 16N between 51W and 52W. Scattered moderate convection is evident farther N and NE from 16N to 18N between 49W and 53W. This NW motion is expected to continue through Thu with an increase in forward speed starting Wed night. Sam will pass well NE of the Northern Leeward Islands Wed, then Puerto Rico on Thu. Slight fluctuation in strength is possible but Sam should remain a major hurricane through Thu. Swells generated by Sam will reach the Lesser Antilles today and impact these islands at least through midweek. 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/ An elongated area of low pressure associated with the remnants of Peter is located a few hundred miles east-southeast of Bermuda. Showers and thunderstorms associated with this system have changed little in organization since yesterday. However, environmental conditions are marginally conducive for some further development, and Peter could briefly become a tropical depression again during the next day or two while it moves northeastward near 10 mph. There is a medium chance of development for the next 48 hours. Disorganized showers and thunderstorms are associated with a broad area of low pressure located several hundred miles SW of the Cabo Verde Islands. Environmental conditions are forecast to be conducive for further development of this disturbance, and a tropical depression is likely to form in a few days while it moves W to WNW at 5 to 10 mph over the central tropical Atlantic. There is a medium chance of development for the next 48 hours. A tropical wave is near the coast of Senegal and just offshore from Sierra Leone in W Africa. Upper-level winds are forecast to be conducive for gradual development, and a tropical depression is likely to form in a few days while the system moves W to WNW at 10 to 15 mph over the far eastern tropical Atlantic. There is a medium chance of development for the next 48 hours. Please read the latest Tropical Weather Outlook at https://nhc.noaa.gov/gtwo.php?basin=atlc&fdays=2 for more details on all three disturbances. ...TROPICAL WAVES... A newly analyzed Atlantic tropical wave is near 16W from the Senegal coast at 16N southward through a low pressure offshore of Sierra Leone, and moving W at 5 to 10 kt. Scattered moderate to isolated strong convection is found from 03N to 08N between the Sierra Leone-Liberia coast and 20W. An Atlantic tropical wave is along 31W from 17N southward and moving W near 15 kt. Scattered moderate to isolated strong convection is present from 03N to 12N between 28W and 36W. Another Atlantic tropical wave is near 41W from 16N southward and moving W near 10 kt. Scattered moderate convection is found from 06N to 10N between 36W and 41W. A Caribbean tropical wave is along 74W from W Hispaniola southward to N Colombia, and moving W at 5 to 10 kt. Scattered showers and thunderstorms are occurring over central Hispaniola and near the Colombia-Venezuela border. ...MONSOON TROUGH/ITCZ... A monsoon trough enters the Atlantic through the coast of Senegal near 14N17W to 08N25W to 08N39W. Scattered moderate to isolated strong convection is observed near and S of the monsoon trough from 02N to 09N between 20W and 28W. No ITCZ is present based on the latest analysis. The eastern end of the E Pacific monsoon trough is triggering numerous heavy showers and scattered thunderstorms over the SW corner of the Caribbean Sea, including the coast of Nicaragua, Costa Rica and W Panama. ...GULF OF MEXICO... A surface trough remains in the NW Gulf just off the Texas- Louisiana coast. This feature is producing scattered showers and isolated thunderstorms over the NW and N central Gulf. 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 surface trough will drift westward toward the Texas coast through tonight. High pressure will persist across the E and central Gulf through mid week. A weak cold front will move into the E Gulf Thu night through Fri. ...CARIBBEAN SEA... Convergent trades are coupling with a mid-level trough to cause scattered showers and thunderstorms across W and central Cuba. An upper-level low W of the Lesser Antilles near 14N65W is inducing scattered showers and isolated thunderstorms over the SE corner of the basin, including the Windward Islands. Refer to the Tropical Waves and Monsoon Trough/ITCZ sections for additional convection in the basin. Moderate to fresh ENE trades and seas at 4 to 6 ft are evident across the central and S central basin. Light to gentle trades and seas of 2 to 3 ft prevail for the rest of the basin. For the forecast, Hurricane Sam will continue on a NW course and pass well NE of the Lesser Antilles Tue and Wed. Swell generated by it will maintain higher seas near the Leeward Islands through Fri, and near Puerto Rico by Wed. Meanwhile, moderate trades will continue over much of the Caribbean through Tue. Fresh trades over the S central Caribbean will diminish to gentle to moderate speeds today. Gentle trades will then prevail over the Caribbean through Fri. ...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 27/2100 UTC. A cold front enters the NW corner of the tropical Atlantic at 30N66W, then curves southwestward 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 reaches northeastward from the central Bahamas to just S of the aforementioned cold front at 28N70W. Scattered showers and thunderstorms are flaring up from the N coast of Cuba across the central Bahamas to NE of the SE Bahamas. Another surface trough curves southwestward from the remnant of Peter near 31N59W to well N of Puerto Rico at 24N66W. Scattered showers and thunderstorms are occurring N of 25N between 57W and 63W. 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, a cold front extending from 30N65W to Grand Bahama Island will stall late today and dissipate through tonight, leaving generally light to gentle breezes and slight seas into mid week W of 65W. Meanwhile, Hurricane Sam will move to 16.4N 52.8W this evening, 17.3N 53.9W Tue morning, 18.1N 55.1W Tue evening, then move to northeast of the Leeward Islands to 19.1N 56.5W by Wed morning. Sam will continue to the northwest reaching 20.2N 58.1W Wed evening, and 21.7N 59.8W Thu morning. Sam will change little in intensity as it moves more 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 Thu. $$ Chan