000 AXNT20 KNHC 231801 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1805 UTC Thu Sep 23 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 1200 UTC surface analysis and satellite imagery through 1745 UTC. ...SPECIAL FEATURES... Recently upgraded Tropical Storm Sam is centered near 10.9N 38.1W at 23/1500 UTC or 1520 nm ESE of the Northern Leeward Islands moving W at 13 kt. Estimated minimum central pressure is 1003 mb. Maximum sustained wind speed is 45 kt with gusts to 55 kt. Satellite imagery depicts a system that is quickly becoming better organized. The imagery shows that it is a rather-compact, with an apparent eye-type feature visible. Scattered moderate to isolated strong convection is noted within about 50 nm of the center, except 60 nm of the center in the SW quadrant. Similar convection marks an outer curved band within 30 nm either side of a line from 13N36W to 13N39W and to 11N41W. Peak seas are up to 13 ft within 60 nm of the center in the NE quadrant and within 30 nm of the center in the NW quadrant. Sam is forecast to become a hurricane on Fri and be near major hurricane intensity by the end of the weekend. Please, read the 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 Peter NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov for more details. A gale-force, non-tropical low pressure system, the remnants of Odette, is located a little more than 520 nm west-northwest of the westernmost Azores. While showers and thunderstorms remain limited near the low, only a small increase in this activity could result in the formation of a subtropical or tropical cyclone while it moves generally southward over marginally warmer waters during the next day or so. Strong upper-level winds are expected to develop over the system beginning tomorrow, which should then limit further development. Additional information on this system, including gale warnings, can be found in High Seas Forecasts issued by the Ocean Prediction Center ocean.weather.gov. Also see the latest Tropical Weather Outlook at www.hurricanes.gov for more details. ...TROPICAL WAVES... A far eastern Atlantic tropical wave has its axis just east of the Cabo Verde Islands near 22W from 05N to 20N. It is moving westward at 10 kt. Scattered moderate convection is seen from 05N to 08N between 19W-22W. A central Atlantic tropical wave has its axis along 51W from 05N to 21N, moving westward at 10-15 kt. No significant convection is noted near the wave axis. ...MONSOON TROUGH/ITCZ... The monsoon trough axis passes through the the Senegalese coast near 15N17W to 09N23W to 08N30W. A segment of the ITCZ extends from 07N40W to 06N48W, and from 06N51W to 06N57W. Aside from convection associated to the tropical wave described above, scattered moderate to strong convection is just inland the coast of Africa within 90 nm south of the trough between 15W-17W. Scattered moderate to isolated strong convection is within 90 nm south of the trough between 17W-19W. Scattered moderate convection is between 120 to 270 nm south of the trough between 23W-27W. GULF OF MEXICO... An early season cold front is moving across the northern Gulf, and as of 15Z it extends from Venice, Florida to 23N90W and to Veracruz, Mexico. The latest ASCAT data passes along with current buoy observations indicate fresh to strong north to northeast winds behind the front. Moderate to fresh northwest winds are are along and just offshore the coast of Mexico from Veracruz to Tampico. Recent altimeter satellite data along with current buoy observations are showing seas in the range of 3-6 ft behind the front. Generally, light to gentle breezes and slight seas are noted south of the front. Satellite imagery reveals a band of Scattered moderate convection identified to be along and within about 60 nm north of the front. Similar convection is confined to the central Bay of Campeche. A drier and stable air mass under high pressure is following in behind the front. For the forecast, the front will continue to move southeastward through tonight, stall from roughly Fort Myers, Florida to the coast of Veracruz, Mexico near 18N95W Fri, then dissipate Sat. Fresh to strong winds will follow the front into tonight, including along the coast of Veracruz where seas may build to 8 ft. Looking ahead, winds and seas will diminish across basin from Sat and into early next week as high pressure builds over the northern Gulf. CARIBBEAN SEA... A sharp upper-level trough extends from the vicinity of the southeastern Bahamas to across eastern Cuba and to the southwestern Caribbean. This trough is acting on an already very moist and unstable environment resulting in enhanced scattered moderate to strong convection to exist over the far south-central and southwestern Caribbean from along the coast of Colombia and Panama to 13N and between 73W-81W. A weakened subtropical ridge north of the area continues to support a pattern of below average winds across the basin. Moderate trade winds are noted over the southeast Caribbean, with generally light to gentle trade winds elsewhere. Seas are relatively low, in the 1-3 ft range, except for slightly higher seas of 2-4 ft over the far southwestern Caribbean. For the forecast, Tropical Storm Sam near 10.9N 38.1W 1003 mb at 1500 UTC, moving W at 14 kt. Maximum sustained winds are 45 kt with gusts to 55 kt. Sam will continue to intensify as it moves across the Atlantic, becoming a hurricane near 12N45W by Fri evening, and reaching 55W east of the Leeward Islands by Mon night. Meanwhile, moderate trade winds will persist over much of the Caribbean into early next week, becoming fresh over the south- central Caribbean starting Fri night as high pressure builds east of the Bahamas. ATLANTIC OCEAN... Please read the Special Features section above for details on newly formed Tropical Storm Sam. The Cumbre Vieja volcano on the island of La Palma in the Canary Islands has been erupting since 19/1410 UTC. A significant ash emission is ongoing in the vicinity of the volcano. 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 issue no later than 23/2300 UTC. As of 15Z, a stationary front extends from near 31N47W to 27N53W to 29N59W to 27N65W and begins to dissipate to 27N73W. A recent ASCAT pass depicts moderate to mainly fresh east to southeast winds north of the stationary front between 56W-59W. A cold front has moved off the southeastern United States coast and extends from 31N79W to inland central Florida. A pre-frontal trough extends from 31N78W to inland South Florida near Stuart. Satellite imagery shows scattered showers and thunderstorms north of 29N and between 75W-79W. Broken to overcast multilayered clouds with embedded areas of rain along with scattered and isolated thunderstorms are seen north of 25N between 57W-64W. The 1009 mb remnant low of Peter is near 23N67W. A trough extends northeast from the low to 26N64W, and southwest from the low to the north- central coast of Hispaniola. An expanding area of scattered moderate to isolated strong convection is well removed to the east of the low from 22N to the stationary front and between 60W- 65W. Similar activity is also from 19N to 22N between 63W-67W. The latest ASCAT pass showed fresh to strong southerly winds with this convective activity. Altimeter data indicates seas up to 7 ft northeast and east of the low from 22N to 28N between 62W-67W. Seas may be slighter higher in the strong convection. The post-tropical cyclone remnant 1010 mb low of former tropical cyclone Rose is near 26N42W. A trough to its southwest extends from 23N45W to 19N48W. A recent altimeter pass has seas up to 11 ft within about 60 nm in the northwest quadrant of this low. This attributed to a large area of northerly swell that is producing seas of 8-12 ft seas north of 22N between 35W-60W. Fresh east to southeast winds are over the eastern semicircle of the low. The low will gradually dissipate through Sat. Aside from the features and related winds and seas already mentioned in this discussion, moderate to occasionally fresh trade winds are noted across the basin along with 4 to 6 ft seas in open waters. For the forecast west of 65W, the remnant low of Peter will dissipate as it drifts northeast of the region through Fri. Meanwhile, a cold front extending from 31N79W to central Florida will stall from near 31N77W to near Fort Pierce, Florida by tonight, then dissipate through early Sun just before a second weak front possibly moves into the region early next week. Farther east, Tropical Storm Sam near is near 10.9N 38.1W 1003 mb at 1500 UTC, moving W at 14 kt. Maximum sustained winds are 45 kt with gusts to 55 kt. Sam will continue to intensify as it moves across the Atlantic, becoming a hurricane near 12N45W by Fri evening, and reaching 55W east of the Leeward Islands by Mon night. $$ Aguirre