000 AXNT20 KNHC 210013 TWDAT Tropical Weather Discussion...UPDATED NWS National Hurricane Center Miami FL 0013 UTC Sat Aug 21 2021 Updated to include the information from the Intermediate Advisories on Hurricane Grace and Tropical Storm Henri 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 2220 UTC. ...SPECIAL FEATURES... Hurricane Grace continues to gain strength over the Bay of Campeche. As of 0300 UTC, the hurricane is centered near 20.7N 95.7W or about 90 nm E of Tuxpan, Mexico, moving W at 9 kt. Maximum sustained wind speed is 85 kt with gusts to 105 kt. Peak seas are currently 36 ft near the center. Estimated minimum central pressure is 967 mb. Grace is producing a large area of strong showers and thunderstorms. Numerous moderate to strong convection is noted across the SW Gulf south of 23N, including the W and central Bay of Campeche. On the forecast track, the center of Grace is forecast to move across the southwestern Gulf of Mexico this evening, and then make landfall along the coast of mainland Mexico within the hurricane warning area tonight. Strengthening is forecast until Grace makes landfall, with rapid weakening expected as Grace moves inland over the mountains of central Mexico. Please read the latest NHC Public Advisory at https://www.nhc.noaa.gov/text/MIATCPAT2.shtml and Forecast/Advisory at https://www.nhc.noaa.gov/text/MIATCMAT2.shtml for more details. Tropical Storm Henri remains on the verge of becoming a hurricane. As of 0300 UTC, it is centered near 31.9N 73.8W at or 235 nm SSE of Cape Hatteras, North Carolina, moving N at 6 kt. Maximum sustained wind speed is 60 kt with gusts to 75 kt. Peak seas are currently 25 ft near the center. Estimated minimum central pressure is 994 mb. Numerous moderate to isolated strong convection is noted from 28N to 33N and between 71W and 75W. A continued forward motion at a faster forward speed is expected through early Sunday. On the forecast track, Henri is expected to make landfall in Long Island or southern New England on Sunday. Strengthening is forecast during the next day or so, and Henri is expected to become a hurricane tonight or Saturday and be at or near hurricane strength when it makes landfall in Long Island or southern New England. Moderate northeast swell from Henri will impact coastal areas from central Florida to Georgia and the Carolinas tonight through Sat. Please read the latest NHC Public Advisory at https://www.nhc.noaa.gov/text/MIATCPAT3.shtml and Forecast/Advisory at https://www.nhc.noaa.gov/text/MIATCMAT3.shtml for more details. ...TROPICAL WAVES... A new Atlantic tropical wave is just off the African coast near 18W-19W from 20N southward and moving W at 10 kt. Scattered moderate isolated strong convection is seen from 11N to 13.5N between 18W and 26W. Another Atlantic tropical wave is along 34W from 20N southward and moving W at 15 to 20 kt. Scattered moderate convection is noted from 05N to 13N between 30W and 37W. A third Atlantic tropical wave is near 46W from 21N southward of and moving W at 15 to 20 kt. Scattered moderate convection is present from 07N to 12N between 43W and 50W. A Caribbean tropical wave is along 66W from 21N southward across Puerto Rico to Venezuela, and moving W at 15 to 20 kt. Scattered showers and isolated thunderstorms are from 14N to 19N between 64W and 73W. This wave has also dragged the ITCZ northward across the the Windward Islands and into E central Caribbean along 63W. Another Caribbean tropical wave is near 76W-77W from E Cuba southward to N Colombia, and moving W near 10 kt. Deep layered dry air is hindering significant convection from flaring up near this wave. ...MONSOON TROUGH/ITCZ... A monsoon trough extends from the coast of Senegal near 14.5N17W to 16.5N22W to 10N50W. The ITCZ then continues from 10N50W to 14N63W. Scattered moderate convection is present near the monsoon trough 05N to 14N between 35W and 42W. Scattered showers are evident near the ITCZ from 09N to 12N between 50W and 56W. The E Pacific monsoon trough extends into the SW Caribbean Sea from near the Costa Rica-Panama border to northern Colombia. Scattered showers and thunderstorms are flaring up across Panama and Costa Rica and their immediate Caribbean coastal waters. ...GULF OF MEXICO... Refer to the Special Features section above for details on Hurricane Grace. Other than Hurricane Grace, a surface ridge reaches southeastward from the NE Gulf through S Florida; providing light to gentle S to SE and seas at 2 to 5 ft east of 90W. Moderate to fresh E to SE winds and seas of 6 to 12 ft are found near the NW and central Gulf, where building SE swell is reaching the Mexican coastlines. Grace will move near the Mexican coast to 20.4N 96.6W tonight then move inland and weaken to a tropical storm near 19.9N 98.9W Sat afternoon. Grace will weaken to a tropical depression near Michoacan, Mexico, Sun morning and dissipate Sun afternoon. High pressure will build in the wake of Grace and prevail through early next week. ...CARIBBEAN SEA... Convergent trade winds are coupling with divergent winds aloft to produce scattered showers and thunderstorms over Hispaniola and the central Caribbean Basin, ahead of the tropical wave along 66W. Moderate to fresh E to SE winds and seas at 5 to 7 ft are noted along the E coast of the Yucatan Peninsula, and the N central basin. Gentle to moderate trades and seas of 4 to 6 ft prevail for the rest of the basin. Moderate to fresh trade winds will dominate the basin through the weekend, except localized pulses of strong winds are possible in the Gulf of Honduras tonight. Early next week, fresh to strong winds will develop over the central Caribbean as high pressure builds across the Atlantic in the wake of Henri. ...ATLANTIC OCEAN... Refer to the Special Features section above for details on Tropical Storm Henri. Convergent winds feeding toward Tropical Storm Henri are producing scattered showers and isolated thunderstorms N of the Bahamas, N of 27N between 75W and 79W. Please read the Tropical Waves and Monsoon Trough/ITCZ sections for additional convection across the Atlantic Basin. The Atlantic ridge stretches from the 1022 mb Bermuda high near 31N55W, extending SW to S Florida. Light to Gentle winds and seas at 3 to 5 ft are found N of 27N between the NW African coast and 67W. Moderate to fresh with locally strong winds and seas of 5 to 8 ft are present N of 28N, E of Tropical Storm Henri between 67W and 71W, and also W of Henri between 75W and 77W. Gentle to moderate NE trades and seas of 4 to 7 ft are found from 16N to 27N between the African coast and Lesser Antilles. Light to gentle SE to S winds and seas at 3 to 4 ft are evident across the Bahamas and near the E Florida coast. Gentle to moderate winds and seas at 4 to 6 ft prevail for the rest of the basin. For the forecast west of 55W, Tropical Storm Henri Henri will strengthen to a hurricane near 32.8N 73.3W tonight, then move to 35.8N 72.3W Sat afternoon. By Sun morning, Hurricane Henri will be well north of the area, off the coast of the Mid-Atlantic U.S. Otherwise, moderate to fresh E to SE winds will prevail E and across the Bahamas Fri through Mon, except for fresh to possibly locally strong winds at night north of Hispaniola and the approaches to the Windward Passage. $$ Stripling/Delgado