000 AXNT20 KNHC 201732 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1805 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 1200 UTC surface analysis and satellite imagery through 1745 UTC. ...SPECIAL FEATURES... Newly upgraded Hurricane Tammy is centered near 14.1N 58.6W at 20/1500 UTC or 140 nm ESE of Martinique, moving WNW at 6 kt. Estimated minimum central pressure is 992 mb. Maximum sustained wind speed is 65 kt with gusts to 80 kt. Peak seas are currently around 21 ft. Tammy has numerous moderate to isolated strong convection observed from 08N to 16.5N and between 54W and 60W. Tammy general motion is expected to continue through this afternoon. A turn toward the northwest is anticipated by this evening, followed by a north-northwestward and northward turn Saturday night through Sunday night. On the forecast track, the center of Tammy will move near or over portions of the Leeward Islands tonight and on Saturday, and then move north of the northern Leeward Islands on Sunday. Gradual strengthening is forecast during the next couple of days, and Tammy is expected to be a hurricane while it moves near or over portions of the Leeward Islands. Heavy rains from Tammy will begin to affect the Leeward and northern Windward Islands later today and into Saturday morning, spreading into the British and U.S. Virgin Islands and Puerto Rico as early as Sunday. 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 reaches the Atlantic through the coast of Guinea-Bissau near 11N16W and continues to 07N24W and then to 08N31W. The ITCZ extends from 08N31W to 10N37W to 07N44.5W. Scattered moderate convection is observed from 01.5N to 11N east of 24W and between 30W and 38W. ...GULF OF MEXICO... A weak surface trough extends from 26N91W to 20N93W and is void of significant convection. The rest of the basin is under a weak high pressure pattern and a dry airmass that suppresses the development of showers and thunderstorms. Moderate or weaker winds prevail across the Gulf, with seas of 3-4 ft in the SE Gulf and 1-3 ft elsewhere. For the forecast, high pressure from the northern Gulf coast into South Carolina will shift SW through Sat, allowing a cold front to sag into the NE Gulf. This front will dissipate as it moves across the eastern Gulf through Sat. Another cold front will follow, moving across the eastern Gulf Sun night through Mon, before stalling southeast of the region by Mon night into early Tue. Looking ahead, high pressure building in the wake of the front will support moderate to fresh E winds Sun night through mid week. ...CARIBBEAN SEA... Please see the Special Features section above for more details on Hurricane Tammy located just east of the Lesser Antilles. A surface trough extends from western Cuba to Belize and is producing scattered moderate convection within 65 nm of its axis. Meanwhile, the eastern Pacific monsoon trough enters the SW Caribbean Sea near 11N83W and continues eastward to northern Colombia near 10N77W. Scattered moderate to isolated strong convection is evident on satellite imagery south of 13N. No deep convection is present elsewhere in the Caribbean. Moderate easterly trade winds and seas of 3 to 5 ft are found in the south-central Caribbean. Outside of the influence of Tammy, moderate or weaker winds and 2 to 4 ft seas are prevalent in the rest of the basin. For the forecast, newly upgraded Hurricane Tammy is near 14.1N 58.6W at 11 AM EDT, and is moving west-northwest at 6 kt. Maximum sustained winds are 65 kt with gusts to 80 kt, and the minimum central pressure is 992 mb. Tammy will move through the northern Leeward Islands through early Sun, reaching 15.1N 59.8W this evening, 16.4N 60.9W Sat morning, 17.9N 61.9W Sat evening, and 19.3N 62.7W Sun morning before continuing north of the area through the early part of the week. Elsewhere, a trough will persist over the northwest Caribbean into Sat. Looking ahead, a weak cold front will move into the northwest Caribbean by late Mon, then stall and weaken from eastern Cuba to northern Belize Tue. ...ATLANTIC OCEAN... Please see the Special Features section above for more details on Hurricane Tammy located just east of the Lesser Antilles. A surface trough enters the tropical Atlantic near 31N61W and continues southwestward to 28N72W. Farther west, another surface trough stretches from 31N76W to 24N79W. These two features combined with divergent flow aloft is resulting in a broad area of scattered moderate convection N of 23.5N and W of 65W. Another area of scattered moderate convection is depicted north of Puerto Rico and it is associated with a deep layer trough. The subtropical ridge centered near 30N36W is the main feature of interest in the central and eastern Atlantic outside of the deep tropics. The pressure gradient between this high pressure and Tammy sustain moderate to fresh E-SE winds from 20N to 31N and between 53W and 67W. Seas in these waters are 6-10 ft. A cold front extends from Morocco to 27N38W and is producing no convection. N of the boundary, moderate N winds and seas of 6 to 10 ft area present. Across the remainder of the basin, winds are mainly moderate with seas of 4 to 7 ft. For the forecast W of 55W, newly upgraded Hurricane Tammy is near 14.1N 58.6W at 11 AM EDT, and is moving west-northwest at 6 kt. Maximum sustained winds are 65 kt with gusts to 80 kt, and the minimum central pressure is 992 mb. Tammy will move through the northern Leeward Islands through early Sun, reaching 19.3N 62.7W Sun morning, then continuing northward to 20.6N 63.3W Sun evening, and 22.0N 63.3W Mon morning, and 24.4N 61.4W by early Tue. Farther west, a weak cold front will move off the northeast Florida coast overnight, then weaken as it moves eastward over the waters north of 27N, before stalling and dissipating east of Bermuda early in the week. A second front will follow, moving off the northeast Florida coast late Sun, reach from Bermuda to West Palm Beach, Florida by early Mon, then stall along 21N Tue. $$ KRV