000 AXNT20 KNHC 192106 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 0005 UTC Fri Oct 20 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 1800 UTC surface analysis and satellite imagery through 1830 UTC. ...SPECIAL FEATURES... Tropical Storm Tammy is centered near 13.7N 56.6W at 19/2100 UTC or 170 nm E of Barbados, moving WNW at 11 kt. Estimated minimum central pressure is 1001 mb. Maximum sustained wind speed is 50 kt with gusts to 60 kt. Peak seas are currently around 21 ft. Numerous moderate to isolated strong convection is noted from 06N to 16N between 50W and 60W. A turn toward the northwest is forecast on Friday, and this motion should continue through Saturday. A northward motion is forecast to begin Saturday night or Sunday. On the forecast track, the center of Tammy will move near or over the Leeward Islands Friday and Saturday, and then move north of the Leeward Islands Saturday night and Sunday. Little change in strength is expected tonight, but gradual strengthening is expected to begin on Friday and continue into this weekend. Tammy is forecast to be at or near hurricane intensity when it moves near the Leeward Islands Friday night and Saturday. Heavy rains from Tammy will begin to affect the Leeward and northern Windward Islands on Friday, spreading into the British and U.S. Virgin Islands and Puerto Rico over the weekend. This rainfall may produce isolated flash and urban flooding, along with isolated mudslides in areas of higher terrain. Swells generated by Tammy will continue to affect portions of the Lesser Antilles during the next few days. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office. 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 Tammy NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov for more details. ...MONSOON TROUGH/ITCZ... The monsoon trough enters the tropical Atlantic near the border of Senegal and Guinea-Bissau at 12.5N16.5W to 07N30W to 02N39W. The ITCZ extends from 02N39W to NE of the coast of Brazil at 01N48W. Numerous moderate to isolated strong convection is observed from 03N to 16N between 22W and 35W. ...GULF OF MEXICO... The Gulf of Mexico remains under the influence of a surface ridge along 26N/27N, which is providing with light to gentle anticyclonic winds across the basin along with 1-3 ft seas, except gentle to moderate NE-E winds from the Straits of Florida to offshore the northern Yucatan Peninsula where seas are 3-5 ft. For the forecast, high pressure extending from the Carolinas to the Texas coast will shift into the southwest through Sat ahead of a cold front moving into the northeast Gulf Fri night. The front will weaken as it moves slowly across the eastern Gulf through Sun and southeast of the Gulf Mon. Looking ahead, high pressure building in the wake of the front will support moderate to fresh NE to E winds Sun night through Tue. ...CARIBBEAN SEA... Please see the Special Features section above for more details on Tropical Storm Tammy located east of the Lesser Antilles. Tropical Storm Tammy is centered near 13.7N 56.6W at 19/2100 UTC or 170 nm E of Barbados, moving WNW at 11 kt. Estimated minimum central pressure is 1001 mb. Maximum sustained wind speed is 50 kt with gusts to 60 kt. A stationary front from eastern Cuba to the Gulf of Honduras has dissipated to a remnant surface trough during the past several hours. Scattered showers and thunderstorms are found from 13N to 22N between 80W and 80.5W. Similar convection is in the SW Caribbean due to the extension of the eastern Pacific Ocean monsoon trough along 09N/10N. Moderate to fresh trades along with 5-7 ft seas, locally to 8 ft near 12N77W, are in the S-central Caribbean. Gentle to moderate winds on either side of the surface trough along with 3-5 ft seas are across the remainder of the basin. For the forecast, Tammy will move to 14.2N 58.2W Fri morning, 15.0N 59.9W Fri afternoon, and 16.4N 61.4W Sat morning. Tammy will strengthen to a hurricane near 17.9N 62.4W Sat afternoon, move to 19.5N 63.1W Sun morning, then continue north of the area through early next week. Elsewhere, a trough will persist over the northwest Caribbean through Sat. Looking ahead, a weak front will move into the northwest Caribbean by Mon then stall through Tue. ...ATLANTIC OCEAN... Please see the Special Features section above for more details on Tropical Storm Tammy located east of the Lesser Antilles. Tropical Storm Tammy is centered near 13.7N 56.6W at 19/2100 UTC or 170 nm E of Barbados, moving WNW at 11 kt. Estimated minimum central pressure is 1001 mb. Maximum sustained wind speed is 50 kt with gusts to 60 kt. A dissipating stationary front extends from SE of Bermuda near 31N60W to across the SE Bahamas to eastern Cuba supporting widely scattered showers and isolated thunderstorms within 240 nm either side of the boundary. A surface trough is analyzed from 31N78W to 27N76W. Fresh to locally strong winds were measured by an earlier ASCAT scatterometer pass from 27N to 31N E of the trough to 70W, along with 5-7 ft seas. Similar winds are from 20N to 27N between 57W and 65W due to a locally tight pressure gradient. Ahead of the front and to the NE of Puerto Rico, upper level diffluence supports a broad area of numerous moderate to scattered strong convection from 16N to 27N between 57W and 67W. The remainder subtropical Atlc is under the influence of a ridge supporting mainly moderate to fresh winds and moderate seas, except gentle to moderate winds N of 29N between 35W and 55W closes to the ridge axis. Some higher seas of 7-10 ft in NW swell are noted behind a cold front which reaches from 31N20W to 29N30W to 30N37W. For the forecast W of 55W, Tammy will intensify to hurricane strength as if moves by the northern Leeward Islands through Sat. Hurricane Tammy will reach 19.5N 63.1W Sun morning, and 21.0N 63.3W Sun afternoon then change little in intensity as it moves northward across the waters east of 65W through Tue. Elsewhere, a stationary front from 31N58W to eastern Cuba will weaken today before dissipating. High pressure will build over the area in the wake of the front. The next frontal system will move offshore the southeastern United States Fri night. Fresh to strong winds and rough seas are forecast north of 27N Fri night through Sat night with this system. $$ Lewitsky