064 AXNT20 KNHC 270555 RRA TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 0605 UTC Mon Sep 27 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 0000 UTC surface analysis and satellite imagery through 0535 UTC. ...SPECIAL FEATURES... Hurricane Sam remains a powerful tropical cyclone, but the anticipated fluctuations in intensity have started. It is centered near 14.7N 50.8W at 27/0300 UTC, or 740 nm ESE of the Northern Leeward Islands, moving NW at 6 kt. Estimated minimum central pressure is 943 mb. Maximum sustained winds are 125 kt with gusts to 150 kt. Peak seas are estimated at 35 to 40 ft just north of the center and similar seas are expected over the next day or two. Satellite imagery this evening indicate that the eye has become covered by convection and there has been an erosion of the western eyewall. Indications are that Sam is undergoing an eyewall replacement, which will cause the intensity to fluctuate. 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. Sam is moving toward the northwest, and this motion is expected to continue for the next few days, along with a gradual increase in forward speed beginning around midweek. Sam is expected to pass well NE of the Leeward Islands on Wed and Thu while accelerating toward the NW. Some fluctuations in intensity are expected during the next day or so. Thereafter, slow weakening is forecast. However, Sam is still expected to 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. A surface trough, associated with the remnants of Peter, is located several hundred miles SE of Bermuda. Recent scatterometer satellite data show an elongated area of low pressure producing fresh to strong southerly winds. Scattered showers and a few thunderstorms are present within 150 nm of the low pressure, mainly in the E quadrant due to strong wind shear. The disturbance has become a little better organized since last night, and environmental conditions are marginally conducive for some further development of this system. Peter could briefly become a tropical depression again during the next day or two while it moves northeastward at about 10 mph. By midweek, environmental conditions are expected to become unfavorable for further development. The disturbance has a medium chance of development over the next 48 hours. Please visit hurricanes.gov for more details. ...TROPICAL WAVES... An Atlantic tropical wave has its axis along 28W, south of 18N, and it is moving W near 15 kt. Interaction between the wave and the monsoon trough allows for scattered moderate to isolated strong convection from 03N to 09N and between 25W and 30W. The northern portion of the wave is devoid of deep convection. Another Atlantic tropical wave has its axis along 38W, south of 17N and it is moving W at 10-15 kt. Interaction between the wave and the monsoon trough results in scattered moderate convection E of the wave axis to 30W and between 04N and 11N. The northern portion of the wave is devoid of deep convection. A Caribbean tropical wave has its axis along 72W, south of 20N, extending from Haiti to W Venezuela and it is moving W near 10 kt. The wave is enhancing the thunderstorm activity over Hispaniola. No deep convection is noted near the wave axis over the Caribbean Sea. ...MONSOON TROUGH/ITCZ... The monsoon trough enters the Atlantic through the coast of The Gambia near 13N17W to 08N25W to 09N32W and to 08N39W. The ITCZ then continues from 08N40W to 09N45W. Scattered moderate to strong convection is observed south of the monsoon trough from 03N to 08N and between 23W and the coast of Africa. The E Pacific monsoon trough enters the Caribbean Sea through the coast of Costa Rica near 11N84W and continues to the coast of NW Colombia. Scattered moderate to isolated strong is seen within 120 nm to the north of the monsoon trough. ...GULF OF MEXICO... A tenacious surface trough remains in the W Gulf, extending from 28N91W to 21N94W, and a few showers continue to flare up near the trough axis. A few showers are also noted over the E Bay of Campeche and off W Florida. However, this activity is quickly losing strength and should dissipate soon. The rest of the basin is under the dominance of dry air, leading to fairly tranquil weather conditions. A recent scatterometer satellite pass indicate fresh NE winds in the Florida Straits, while gentle to moderate anticyclonic winds prevail in the remainder of the Gulf. Seas in the SE Gulf are 2-4 ft, with the highest seas occurring in the Florida Straits. Elsewhere, seas are 1-3 ft. The aforementioned surface trough will drift westward toward the Texas coast through Mon night. Moderate winds will prevail north of the trough through Mon morning. 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 bring moderate to fresh winds over most of the Gulf on Fri through Sat. ...CARIBBEAN SEA... Favorable upper-level atmospheric dynamics and diurnal heating in the northern Caribbean allowed for the development of afternoon and evening thunderstorms across the Greater Antilles. The storm activity is decreasing at this hour, but some of the storms have moved south and offshore and are affecting the waters within 60 nm of Puerto Rico and the Dominican Republic. A few showers are also seen in the E Caribbean, near the Lesser Antilles, while fairly tranquil conditions prevail in the rest of the basin. Recent satellite-derived wind data show fresh trades within 100 nm of the coast of Colombia and NW Venezuela, including the waters surrounding the ABC islands. Moderate to locally fresh trades are present elsewhere in the Caribbean Sea. Sea of 3-6 ft are occurring in the central Caribbean, with the highest seas materializing in the south-central and SW Caribbean. Elsewhere, seas are 1-3 ft. Hurricane Sam near 14.7N 50.8W 943 mb at 11 PM EDT moving NW at 6 kt. Maximum sustained winds 125 kt gusts 150 kt. Sam will move to 15.3N 51.6W Mon morning, 16.2N 52.8W Mon evening, 17.0N 53.9W Tue morning, 17.8N 55.0W Tue evening, 18.7N 56.3W Wed morning, and 20.0N 58.0W Wed evening. Sam will change little in intensity as it moves near 23.4N 61.0W late Thu. Meanwhile, moderate trades will continue over much of the Caribbean through Tue. Fresh trades over the south- central Caribbean will diminish to gentle to moderate speeds by 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. Swells generated by Sam are forecast to reach the Lesser Antilles by late Mon into Tue. ...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. ANother cloud mainly composed of SO2 is 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 27/0900 UTC. A cold front traversing the NW Atlantic enters the tropical Atlantic near 31N69W and extends to 28N77W, about 100 nm NE of the NW Bahamas. A few showers are observed near the frontal boundary. Nearby, a surface trough extends from 30N69W to 24N77W in the central Bahamas. Moderate scattered convection is seen on satellite imagery within 100 nm of the trough axis. Satellite- derived wind data depict moderate to fresh cyclonic winds surrounding the trough, with the highest winds occurring near the convection. Farther east, a cold front extends from a 1012 mb low pressure SW of the Azores and enters the tropical Atlantic near 31N29W and transitions into a stationary front that extends to 23N34W and to 22N45W. The convection near the boundary is quite meager, consisting of a few showers and isolated thunderstorms. However, satellite-derived wind data indicate that fresh to strong southerly winds are occurring N of 25N and within 150 nm to the E of the frontal boundary. The scatterometer satellite data also depict fresh to locally strong NE winds N of 22N and E of 20W, with the strongest winds occurring near the coast of NW Africa. Outside of the influence of Hurricane Sam, the rest of the basin experiences moderate or weaker winds. Seas are 4-8 ft, with the highest seas occurring near the areas described above. A cold front is pressing southward off the Florida coast with a pre-frontal trough stretching from 30N69W to 24N77W. This front will weaken by late Mon into early Tue. Expect showers and thunderstorms along this boundary through Mon night. Gentle to moderate winds will prevail through most of the week. Stronger high pressure will build southward over the NW and north- central offshore waters late in the week, bringing moderate to fresh winds especially off the Florida coast. Hurricane Sam near 14.7N 50.8W 943 mb at 11 PM EDT moving NW at 6 kt. Maximum sustained winds 125 kt gusts 150 kt. Sam is forecast to continue on its current motion over the next few days as it slowly weakens reaching near 28N63W by late Fri, with maximum sustained winds 105 kt gusts 130 kt. Swells generated by Sam are expected to spread westward across the forecast waters late in the week. $$ DELGADO