000 AXNT20 KNHC 291044 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1205 UTC Wed Sep 29 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 1030 UTC. ...SPECIAL FEATURES... Hurricane Sam was centered near 18.9N 56.2W at 29/0900 UTC or 400 nm E of the Northern Leeward Islands moving NW at 8 kt. Estimated minimum central pressure is 950 mb. Maximum sustained wind speed is 115 kt with gusts to 140 kt. Maximum significant wave heights are 35 ft near the center, while the 12 ft seas extend out as far as 180 n mi from the center. Latest satellite imagery shows a cloud-filled eye about 15 nm in diameter. Numerous strong convection is within 90 nm of the center in the E semicircle and within 50 nm of the center in the W semicircle. Scattered moderate isolated strong convection is elsewhere within 200 nm N semicircle, 120 nm SE quadrant and 90 nm SW quadrant. Sam will continue moving northwest with an increase in forward speed during the next couple of days. A turn toward the north is forecast by Friday. On the forecast track, Sam will pass well to the east and northeast of the northern Leeward Islands through tonight. Some fluctuations in intensity are expected during the next couple of days, but Sam is forecast to remain a major hurricane through late this week. Swells generated by Sam will impact the Lesser Antilles during the next several days. Swells are expected to reach Bermuda and the Bahamas in a day or two, and then spread to the United States east coast by this weekend. These swells could cause life-threatening surf and rip current conditions. Please read the latest High Seas Forecast issued by the National Hurricane Center at website https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov for more details. East Atlantic Gale Warning: A 1007 mb low pressure near 07N23W is along a tropical wave that extends along 23W from 02N-15N, moving W at 10-15 kt. Numerous strong convection from 06N-11N between 21W-26W is showing signs of organization. Scattered moderate convection is elsewhere from 04N-12N between 20W-30W. Environmental conditions are conducive for additional development, and a tropical depression or tropical storm is likely to form later today or tonight while the disturbance moves west-northwestward at 10 to 15 mph over the eastern tropical Atlantic. This system has a high chance of formation in the next 48hours. Please read the latest High Seas Forecast issued by Meteo- France at website http://weather.gmdss.org/II.html regarding the gale warning for this system. A 1009 mb low pressure is near 07N32W. Scattered moderate convection from 02N-07N between 30W-39W remains disorganized. Although environmental conditions are generally conducive for development during the next day or so, interaction of this system with the low pressure area located to its east is likely to hinder development after that time. The system is forecast to drift west-northwestward over the next few days. This system has a medium chance of tropical cyclone formation. Please refer to the latest NHC Tropical Weather Outlook at www.hurricanes.gov for more details on the two tropical disturbances. ...TROPICAL WAVES... A central Atlantic tropical wave is along 40W from 17N southward, moving W at 15 kt. Scattered moderate convection is within 100 nm east of the wave from 04N to 11N. A western Caribbean tropical wave is along 81W south of 17N to across Panama. It is moving W near 10 kt. Scattered moderat convection is noted from 10N to 12N between 79W and 83W. This activity is being further enhanced by the eastern segment of the east Pacific monsoon trough. ...MONSOON TROUGH/ITCZ... A monsoon trough enters the Atlantic through the coast of Mauritania near 17N16W to the aforementioned 1007 mb low near 07N23W to the aforementioned 1009 mb low near 07N32W to 05N39W. The ITCZ extends from 04N42W to the coast of French Guiana near 04N52W. Aside from convection mentioned in the sections above, scattered moderate convection is noted along the ITCZ from 04N to 08N between 41W and 52W. GULF OF MEXICO... Scattered to numerous moderate convection continues over much of the northwest Gulf of Mexico north of 26N and west of 87W. This is occurring in an area where strong upper-level diffluence is co- located with mid-level SW winds, transporting ample moisture northward from the tropics. Expect more scattered showers and tstorms over the northwest and north-central Gulf of Mexico today. A 1016 mb high pressure is centered near 29N84W in the northeast Gulf and the ridge extending acorss most of the Gulf. Thunderstorms are also occurring over the southern Bay of Campeche. Overnight ASCAT pass shows fresh SE to S winds near the coast of south Texas and northeast Mexico. Fresh E winds are noted just off the coast of the NW Yucatan Peninsula. Light to gentle winds are seen in the NE Gulf near the high pressure. Moderate wind speeds are elsewhere. Seas of 2 to 4 ft cover most of the Gulf, except 1 to 2 ft in the NE Gulf. For the forecast, weak high pressure will stay in place over Gulf through Fri. Moderate to locally fresh southerly winds are expected in the western Gulf through Thu with gentle winds in the eastern Gulf. A weak cold front will press southward over the eastern Gulf on Fri and weaken by Sat. Stronger higher pressure will build across the region through Sat. Moderate to fresh winds are expected to prevail in the eastern Gulf with gentle to moderate winds in the western Gulf through the weekend. CARIBBEAN SEA... A recent ASCAT pass shows gentle trade winds across most of the basin, except for moderate in the south-central Caribbean. Seas are averaging 2 to 3 ft across the basin, except 3 to 4 ft over the south-central and SE Caribbean. Scattered moderate showers and tstorms are noted in the SW and south-central Caribbean south of 13N between 71W-81W. Isolated showers and tstorms are noted near Hispaniola and just south of the coast of central Cuba. For the forecast, moderate trades will continue over much of the Caribbean tonight. Gentle trades will then prevail over the Caribbean through Fri. Swells generated by Hurricane Sam are forecast to continue off the Leeward Islands through Thu and will impact the Mona and Anegada Passages today through Fri. The hurricane will pass well northeast of the northern Leeward Islands tonight into early Thu, remaining over the open Atlantic. ATLANTIC OCEAN... Please read the Special Features section above for details on Hurricane Sam and on two tropical disturbances in the eastern part of the Atlantic Basin. The Cumbre Vieja volcano on the island of La Palma in the Canary Islands near 28.6N 17.8W has been erupting since September 19th. Medium concentration of volcanic ash is expected near, and up to 40 nm southeast of the volcano. 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/ for details. The next advisory will be issued no later than 29/0900 UTC. Over the west Atlantic, a surface trough extends from 28N60W to 23N70W. Scattered showers and tstorms are noted along and N of the trough from 25N-27N between 66W-69W. A 1017 mb high pressure is near 31N78W. Gentle winds cover most of the area west of 62W except for moderate to fresh E winds in the Florida Straits. Seas are 2 to 4 ft west of 70W, but higher farther east due to swell from Hurricane Sam. Over the eastern Atlantic, a surface trough extends from 22N39W to 30N37W. Scattered moderate showers and tstorms are along the portion of the trough north of 25N. The Tuesday evening ASCAT pass showed strong to near gale force NE winds off the coasts of Morocco and Western Sahara, extending SW through the Canary Islands, and including most of the area from 21N-29N, east of 30W. Seas are likely 9 to 11 ft within these areas. For the forecast, Hurricane Sam will move to near 22N60W Thu morning, 26N62W Fri morning, 29N62W Fri evening, and near 35N58W Sat evening. In addition to hurricane conditions northeast of the Leeward Islands through tonight, expect rough seas in the form of swell from Sam east of 70W Thu and Fri. Farther west, a weak pressure pattern will maintain light to gentle breezes and slight seas through Thu. A cold front will move from the Carolinas to the central Bahamas Fri and Sat, then stall and dissipate through late Sun. $$ AReinhart