000 AXNT20 KNHC 240940 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 0605 UTC Tue Oct 23 2023 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 0545 UTC. ...SPECIAL FEATURES... Hurricane Tammy is centered near 22.9N 63.1W at 24/0300 UTC or 570 nm S of Bermuda, moving NE at 8 kt. Estimated minimum central pressure is 987 mb. Maximum sustained wind speed is 65 kt with gusts to 80 kt. Peak seas near the center are estimated at 27 ft. Numerous moderate convection is seen within 250 nm north and east of the center. Tammy general motion is expected to continue through Wednesday. A turn toward the north at a slower forward speed is forecast to begin on Thursday. Slight strengthening is possible during the next day or two. Weakening is expected after that. Tammy is forecast to become a post- tropical cyclone on Thursday. Swells generated by Tammy will continue to affect portions of the Leeward Islands, the British and U.S. Virgin Islands, and Puerto Rico during the next few days. These swells are likely to cause life-threatening surf and rip current conditions. Please read the latest HIGH SEAS FORECAST issued by the National Hurricane Center at the website https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest Tammy NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov for more details. Tropical Depression Twenty-One is centered near 12.4N 83.4W at 24/0300 UTC or 30 nm NE of Bluefields Nicaragua, moving NW at 4 kt. Estimated minimum central pressure is 1007 mb. Maximum sustained wind speed is 25 kt with gusts to 35 kt. Peak seas near the center are less than 8 ft. Numerous moderate isolated strong convection is occurring within 260 nm of the center in the N semicircle and 130 nm S semicircle. The depression motion is expected to continue tonight. On the forecast track, the depression will move inland over the next few hours over eastern Nicaragua. Little change in strength is forecast. The depression is forecast to dissipate inland over Nicaragua tomorrow. Heavy rains from the depression will continue to impact portions of Nicaragua through Tuesday night with heavy rainfall spreading into Honduras during the day on Tuesday. This rainfall is likely to produce flash and urban flooding, along with possible mudslides in areas of higher terrain. Please read the latest NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov for more details. Western Atlantic Very Rough Seas: High pressure will move off the east coast of the United States, and build north of the forecast area through midweek. The pressure gradient will tighten between Hurricane Tammy and the area of building high pressure. The tightening pressure gradient will help to develop a very large area of strong to near-gale force NE winds and very rough seas of 12 to 17 ft across much of the area from 23N to 31N, between the east coast of Florida and 60W, starting this afternoon and continuing through Friday. Mariners should either seek to avoid this region, or use extreme caution in this area, depending on your vessel type and cargo. ...MONSOON TROUGH/ITCZ... A monsoon trough enters the Atlantic along the coast of west Africa near Guinea-Bissau from 10N15W to 06N21W to 06N26W. The ITCZ extends from 06N26W to 08.5N35W, then continues west of a surface trough from 09N40.5W to 09.5N48W to 13.5N51.5W. A surface trough is analyzed from 12N37W to 09N37W to 07N47W. Scattered moderate isolated strong convection is noted near the monsoon trough from 06.5N to 10N between west of 22W. Similar convective activity is noted near the ITCZ from 08N to 17N between 41W and 55W. Additionally, similar convection is near the surface trough from 05N to 11.5N between 33W and 40W. ...GULF OF MEXICO... Little to no shower activity is noted across the basin currently. A broad surface ridge dominates the Gulf. Moderate to fresh SE winds and seas of 4 to 6 ft seas are seen over the western Gulf. Moderate E winds and 2-4 ft seas are over the SE Gulf. The northeast Gulf is experiencing gentle NE to E winds and 1-3 ft seas. For the forecast, high pressure building north of the area will lead to increasing winds early this week, with fresh to locally strong E winds and building seas through Thu night. ...CARIBBEAN SEA... Please read the Special Features section above for details on Tropical Depression Twenty-One. Outside of TD Twenty-One, Scattered showers and tstorms are noted across the western Caribbean, west of 76W. Moderate to locally fresh NE winds are present in the NW Caribbean and Windward Passage, with seas 3 to 5 ft. Elsewhere, winds are light to gentle with 1 to 3 ft seas. The exception is in the Mona and Anegada Passages, where swell from distant Hurricane Tammy is causing seas of 4 to 6 ft. For the forecast, Tropical Depression Twenty-One is near 12.4N 83.4W at 11 PM EDT, and is moving northwest at 4 kt. Maximum sustained winds are 25 kt with gusts to 35 kt, and the minimum central pressure is 1007 mb. Twenty-One will become a remnant low and move to 13.1N 84.2W Tue morning, and dissipate Tue evening. Otherwise, fresh to occasionally strong winds will prevail in the lee of Cuba and in the Windward Passage through the week. Winds will briefly increase to fresh to strong south of Hispaniola Wed night and Thu. ...ATLANTIC OCEAN... Please read the Special Features section at the beginning about Hurricane Tammy. A weak stationary front curves west-southwestward from 31N63W to 29N78W. No significant convection is found near the front. A dissipating stationary front extends southwestward from near 31N61W to the SE Bahamas to eastern Cuba. Scattered moderate convection is noted within 150 nm SE of the dissipating stationary front, mainly east of 65W. Elsewhere west of 60W, outside of the area being affected by Tammy, winds are fresh out of the NE with seas of 5 to 7 ft. A large dome of 1022 mb high pressure near 32N34W is providing gentle to moderate winds across the eastern Atlantic, east of 55W. Seas range from 4 to 8 ft over this area, except as high as 9 ft in the far east Atlantic, to the north of the Cabo Verde Islands. For the forecast W of 55W, Hurricane Tammy is near 22.9N 63.1W at 11 PM EDT, and is moving northeast at 8 kt. Maximum sustained winds are 65 kt with gusts to 80 kt, and the minimum central pressure is 987 mb. Tammy will move to 23.6N 62.2W Tue morning, 24.7N 60.8W Tue evening, and 26.5N 59.2W Wed morning. Hurricane Tammy will be near 28.5N 58.3W Wed evening, 30.0N 58.6W Thu morning, and then become extratropical near 31.1N 59.7W Thu evening. Tammy will change little in intensity as it moves E of Bermuda late Fri. A slow-moving cold front currently from near 31N63W to the central Bahamas will gradually stall Tue then dissipate by Wed. The pressure gradient between this front, Tammy, and high pressure building in off the east coast of the United States will lead to the development of a broad area of NE winds and rough seas across much of the area west of the frontal boundary Tue through the week. $$ KRV