000 AXNT20 KNHC 262247 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 0005 UTC Sun Sep 26 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 1800 UTC surface analysis and satellite imagery through 2200 UTC. ...SPECIAL FEATURES... Hurricane Sam, a category 4 hurricane on the Saffir-Simpson Wind Scale is centered near 14.2N 50.5W at 26/2100 UTC, or 765 nm ESE of the Northern Leeward Islands, moving WNW at 6 kt. Estimated minimum central pressure is 938 mb. Maximum sustained winds are 130 kt with gusts to 160 kt. Peak seas are estimated at 35 to 40 ft just north of the center. Satellite imagery throughout the afternoon has shown Sam attempting to become an annular hurricane with a 15 nm wide eye. Numerous moderate to strong convection is seen within 60 nm of the center. Scattered moderate convection is found elsewhere within 150 nm of the center. A WNW motion should continue through tonight, then a turn toward the NW with little change in speed will begin on Mon. Sam is expected to pass well NE of the Leeward Islands on Wed and Thu while accelerate toward the NW. Some slight weakening is possible starting Mon afternoon but Sam should remain a major hurricane through midweek. Swells generated by Sam will begin to impact the Lesser Antilles on Mon. Please read the latest High Seas Forecast issued by NHC at http://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest NHC Public Advisory and Forecast/Advisory at https://hurricanes.gov for more details. ...TROPICAL WAVES... An Atlantic tropical wave is near the Cabo Verde Islands along 26W from 17N southward, moving west near 15 kt. Associated convection is described below. Another Atlantic tropical wave is along 37W from 16N southward and moving W at 10 to 15 kt. Associated convection is described below. A Caribbean tropical wave is near 71W from the central Dominican Republic southward into NW Venezuela, and moving W near 10 kt. Scattered showers and isolated thunderstorms are occurring over NW Venezuela and northern Colombia, while no associated convection is seen over water. ...MONSOON TROUGH/ITCZ... The monsoon trough exits the coast along the Liberia-Sierra Leone border near 07N11.5W to 10N23W to low pres 1011 mb near 08N35W to 08.5N39W. The ITCZ then continues from 04.5N40W to 04N48W. Scattered moderate to strong convection is flaring up near and S of the monsoon trough off the African coast from 03N to 12N extending westward to 22W, and is also seen from 04.5N to 09.5N between 24W and 38W, and from 05N to 08.5N between 42W and 46W. Scattered heavy showers and thunderstorms are occurring near the coast of Honduras, Nicaragua, Costa Rica and Panama, and adjacent waters between the eastern end of the E Pacific monsoon trough and 12N. ...GULF OF MEXICO... A persistent surface trough curves northeastward from the central Bay of Campeche to the N central Gulf near 27N91W. Scattered showers and isolated thunderstorms are seen over both the central Bay of Campeche and Gulf. Otherwise modest surface ridging along with drier air at mid levels are supporting light to gentle winds and seas of 2 to 4 ft across much of Gulf. The aforementioned surface trough will drift westward toward the Texas coast through Mon night. Otherwise, moderate winds prevail north of the trough. High pressure presently over the area will remain in place trough Thu, then be replaced by slighter stronger high pressure that will build southward over the area Fri and Fri night. This will lead to freshening of the winds over most sections of the Gulf Fri and Fri night. ...CARIBBEAN SEA... Refer to the Monsoon Trough/ITCZ section for convection in the Caribbean Basin. Increasing surface pressure gradient between the eastern end of the Pacific monsoon trough and the Atlantic ridge is causing moderate to locally fresh trades with seas at 5 to 7 ft across the central and S central basin. Light to gentle trades and seas of 2 to 4 ft prevail for the rest of the basin. Major Hurricane Sam is going to pass well E of the Windward Islands Mon, and then well NE of the Leeward Islands during midweek. Swells generated by Sam will cause seas to build across the waters of the Windward Islands Mon, and the Leeward Islands Tue. Meanwhile, moderate trades will continue over much of the Caribbean into early next week. Fresh trades over the S central Caribbean will diminish to gentle to moderate speeds Tue. Mainly gentle trades will be over the rest of the Caribbean through Thu, while fresh trades will follow in the wake of Sam across the Tropical N Atlantic waters. ...ATLANTIC OCEAN... Please read the Special Features section above for details on Hurricane Sam. The Cumbre Vieja volcano on the island of La Palma in the Canary Islands has been erupting since 19/1410 UTC. Significant volcanic ash is mainly in the vicinity of the volcano below 5000 ft. Residual SO2 is also drifting to the NE. Marine and aviation interests should monitor this on-going situation by reading Volcanic Ash Advisory issued by Meteo-France at http://vaac.meteo.fr/volcanoes/la-palma/. The next advisory will be issued no later than 26/2100 UTC. A surface trough reaches northeastward from the central Bahamas to SW of Bermuda near 29N72W. Scattered showers and thunderstorms are occurring within 60 nm W and 180 nm SE of this feature, including the NW and central Bahamas. Another surface trough curves north-northeastward from well N of Puerto Rico at 25N66W through a 1015 mb low pressure centered at 27.5N62.5W to beyond 31N at 62W. Numerous moderate isolated strong convection is present from 26N to 30N between 58W and 62W. Scattered moderate convection is evident farther W from 25N to 27N between 62W and 66W. A cold front curves southwestward from a low pressure SW of the Azores near 31N31W to 24N34W to near 23N44W. Scattered showers and isolated thunderstorms are present up to 215 nm S and E of this boundary. An area of moderate to fresh with locally strong SE to S winds and seas at 5 to 7 ft are found SE of the low, N of 25N between 25W and 31W. Refer to the Tropical Waves and Monsoon Trough/ITCZ sections for additional convection across the basin. Other than the winds and seas SE of the aforementioned low, light to gentle with locally moderate winds and seas of 4 to 5 ft are noted N of 20N between 20W and the Georgia-Florida coast. Moderate NE trades and seas at 5 to 6 ft are occurring near the Canary Islands N of 20N between the NW African coast and 20W. Outside the influence of Hurricane Sam, light to gentle with locally moderate trades and seas of 4 to 6 ft exist from 10N to 20N between the African coast and Lesser Antilles. Gentle to moderate monsoon winds and seas at 5 to 7 ft prevail for the remainder of the basin. The surface trough extends from NE from the central Bahamas will gradually shift eastward through Tue night. Farther east, major Hurricane Sam located over the tropical N Atlantic waters is forecast to turn NW on Mon and this motion should continue through midweek, passing well NE of the Leeward Islands. It is anticipated to slowly weaken as it reaches near 22N60.5W by Thu afternoon with maximum sustained winds 110 kt gusts 135 kt. $$ Stripling