000 AXNT20 KNHC 281810 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1805 UTC Tue Sep 28 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 1530 UTC. ...SPECIAL FEATURES... Sam, a Category 4 Hurricane was centered near 17.5N 54.3W at 28/1500 UTC or 505 nm E of the Northern Leeward Islands, and moving NW at 7 kt. Estimated minimum central pressure is 952 mb. Maximum sustained winds are 115 kt with gusts to 140 kt. Seas are peaking at 36 to 39 ft near the center, and from 28 to 35 ft up to 70 nm farther out. Latest satellite imagery shows a cloud-filled eye. Numerous moderate to scattered strong convection is up to 75 nm in a NE semicircle, and up to 55 nm in a SW semicircle. Scattered moderate convection is present up to 60 nm farther out NW, N and NE of the center. A NW motion will continue through Thu morning with a gradual increase in speed by Wed, then follow by a turn toward the N by Friday. On the forecast track, Sam will pass well NE of the Northern Leeward Islands Wed and then Puerto Rico Thu. Some fluctuations in intensity are expected during the next couple of days, but Sam is forecast to remain a major hurricane through late this week. Swells generated by Sam will impact the Lesser Antilles for the next several days. Swells are expected to reach Bermuda and the Bahamas within a couple of days, and then spread to the United States east coast late this week. These swells could cause life-threatening surf and rip current conditions. 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://nhc.noaa.gov/cyclones/ Showers and thunderstorms are showing signs of organization in association with a tropical wave and broad area of low pressure located about 530 nm SSE of the Cabo Verde Islands. Environmental conditions are conducive for development, and a tropical depression is likely to form in a day or two while the disturbance moves west- northwestward at 10 to 15 mph over the eastern tropical Atlantic. There is a high chance for formation in the next 48 hours. A broad area of low pressure located about 600 nm SW of the Cabo Verde Islands continues to produce an area of disorganized showers and thunderstorms. Environmental conditions are conducive for gradual development, and a tropical depression is likely to form during the next couple of days while the system moves westward to west-northwestward at 5 to 10 mph over the central tropical Atlantic. There is a high chance for formation in the next 48 hours. A well-defined low pressure area associated with the remnants of Peter is located about 350 miles ENE of Bermuda. The associated showers and thunderstorms have increased a little this morning, but are still not well organized. This system could become a short-lived tropical depression while moving northeastward at about 10 mph before upper-level winds increase on Wednesday. There is a medium chance for formation in the next 48 hours. In addition, the Ocean Prediction Center (OPC) has issued a Gale Warning for this system, please visit oceanweather.com for more information. Please refer to the latest NHC Tropical Weather Outlook at www.hurricanes.gov for more details on all three tropical disturbances. ...TROPICAL WAVES... An Atlantic tropical wave is SSE of the Cabo Verde Islands near 20W from 16N southward through the aforementioned low pressure near 07N20W, and moving W at 10 to 15 kt. Numerous moderate to strong convection is flaring up from 03N to 10N between 15W and 22W. Refer to the Special Features section above for the formation potential of this wave. Another Atlantic tropical wave is along 37W from 16N southward and moving W near 15 kt. Scattered moderate convection is seen from 04N from 11N between 34W and 38W. The weak Atlantic tropical wave previously located near 43W has been absorbed by the strong ridge to the SE of Hurricane Sam. A Caribbean tropical wave is along 79W from W Jamaica southward to E Panama, and moving W near 10 kt. Enhanced by the E Pacific monsoon trough, numerous heavy showers and scattered thunderstorms are occurring across Panama and NW Colombia, including adjacent waters. ...MONSOON TROUGH/ITCZ... A monsoon trough enters the Atlantic near the Guinea Bissau-Guinea border near 11N15W through the aforementioned 1010 mb low pressures 07N20W and 09N33W to 06N39W. Numerous moderate to strong convection is present from 03N to 09N between 22W and 26W. Scattered moderate convection is found farther W from 03N to 12N between 26W and 34W. Latest satellite scatterometer and altimetry data reveal moderate to fresh with locally strong monsoon winds and seas of 7 to 9 ft near and S of the monsoon trough, from 01N to 07N between 18W and 30W. ...GULF OF MEXICO... A weak but persistent surface trough over S Texas and Louisiana is triggering scattered showers and thunderstorms across the N central Gulf. Locally moderate winds and seas up to 4 ft are possible near these showers and thunderstorms. Otherwise, a broad ridge of high pressure extending southwestward from N Florida to central Mexico continues to promote light to gentle winds and seas of 2 to 3 ft for much of the Gulf. For the forecast, the ridge will maintain light to gentle winds and slight seas across the Gulf through mid week. Moderate to fresh winds will follow a weak cold front that will move into the E Gulf toward the end of the week and then exit the area during the weekend. Moderate to locally fresh winds are also expected across the SE Gulf later in the week due to a persistent trough in that region. ...CARIBBEAN SEA... Modest convergent trade winds are causing isolated thunderstorms near the Cayman Islands and the SE basin. Refer to the Tropical Waves section for additional convection in the basin. Moderate to locally fresh trades and seas at 4 to 5 ft are evident over the S central basin. Light to gentle trades and seas of 2 to 3 ft prevail for the rest of the Caribbean Basin. For the forecast, major Hurricane Sam will pass well NE of the Northern Leeward Islands Wed, then turn northward to SE of Bermuda through early Sat. Meanwhile, moderate trades will continue over much of the Caribbean today. Gentle trades will then prevail over the Caribbean through Fri. Swells generated by Sam are forecast to persist near the Leeward Islands through the middle of the week. ...ATLANTIC OCEAN... Please read the Special Features section above for details on Hurricane Sam and the tropical disturbances in the Atlantic Basin. The Cumbre Vieja volcano on the island of La Palma in the Canary Islands has been erupting since 19/1410 UTC. Based on footage from nearby webcams, the volcanic ash plume is reaching near 20,000 ft or 6,000 meters; and is drifting eastward. Marine and aviation interests should monitor this ongoing 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 28/2100 UTC. A stationary front meanders southwestward from near Bermuda across 31N65W to the central Bahamas. A surface trough is also in the vicinity, curving northeastward from S of this front at 26N70W to beyond 31N58W. These features are producing scattered showers and isolated thunderstorms N of 24N between 57W and the central Bahamas. In the E central Atlantic, a surface trough near 28N33W is generating scattered moderate convection W of the Canary Islands, N of 26N between 27W and 37W. Refer to the Tropical Waves and Monsoon Trough/ITCZ sections for additional convection across the Atlantic Basin. N of 22N, light to gentle winds and seas at 3 to 4 ft are found between 62W and the Georgia-Florida coast; gentle winds with locally moderate winds and seas of 5 to 7 ft are seen between 30W and 62W. Farther E, moderate to fresh with locally strong NE trades and seas at 8 to 11 ft are present near the Canary Islands, N of 20N between the NW African coast and 30W. Outside the influence of Hurricane Sam, gentle to moderate trades and seas of 5 to 7 ft exit from 10N to 22N/20N between the African coast and the Lesser Antilles. Besides stronger monsoon winds and higher seas mentioned in the Monsoon Trough/ITCZ section, mainly gentle monsoon winds and seas at 4 to 7 ft prevail across the remainder of the basin. For the forecast W of 50W, light to gentle breezes are expected to prevail with slight seas through Thu W of 65W. Meanwhile, Hurricane Sam was near 17.5N 54.3W 952 mb at 28/1500 UTC and moving NW at 7 kt. Maximum sustained winds are 115 kt with gusts to 140 kt. Sam will move to 18.2N 55.1W this evening, 19.2N 56.5W Wed morning, 20.5N 58.1W Wed evening, 22.0N 59.6W Thu morning, 24.0N 60.9W Thu evening, and 26.6N 61.5W Fri morning. Sam will change little in intensity as it moves north of the area by early Sat, staying east of Bermuda. At a minimum, expect rough seas in the outer swell from Sam from mid to late week, reaching as far west as 70W by Thu. $$ Chan