000 AXNT20 KNHC 151750 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1805 UTC Wed Sep 15 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... Tropical Depression Nicholas is centered near 30.4N 92.8W at 15/1500 UTC or 25 nm NE of Lake Charles LA moving ENE at 4 kt. Estimated minimum central pressure is 1004 mb. Maximum sustained wind speed is 25 kt with gusts to 30 kt. The center of Nicholas is largely devoid of deep convection, with most of the activity located over the Mississippi Valley and extending to the NW Gulf of Mexico. The forward speed is expected to slow through the next 24 hours before a gradual turn to the north prior to dissipation. Continued weakening is forecast during the next 48 hours with the center of circulation possibly becoming quite diffuse by late Thursday. However, heavier rainfall will continue to remain a threat as tropical moisture persists across the Gulf Coast region. Nicholas is expected to produce additional rainfall amounts of 3 to 6 inches across the central Gulf coast in central to southeastern Louisiana, southern Mississippi, southern Alabama and the Florida Panhandle through Friday, with isolated storm totals of 10 inches possible. Life-threatening flash flooding impacts, especially in urban areas, remain a possibility in these areas. Swells generated by Nicholas affecting portions of the NW Gulf will continue to subside today. The Weather Prediction Center is using the advisories on TD Nicholas and they can be found under AWIPS header TCPAT4, WMO header WTNT34 KWNH, and on the web at http://www.wpc.ncep.noaa.gov. A surface trough extends from 30N71W to 23N75W reaching the central Bahamas. A 1011 mb low pressure is analyzed along the trough axis near 28N73W and satellite imagery indicate that it is becoming better defined. This system is producing a large area of disorganized showers and thunderstorms, mainly over the eastern semicircle, from 20N and 30N, and between 64W to 74W. Recent scatterometer satellite data show fresh to strong SE-S winds in the area of convection. Environmental conditions are expected to become more conducive for development, and a tropical depression is likely to form during the next day or two while the system moves north- northwestward to northward off the southeast U.S. coast. The Air Force Hurricane Hunters are currently enroute to investigate the disturbance. This system has a high chance of development in the next 48 hours. Regardless of development, increased winds and building seas are expected north of 27N between 68W and 75W today and tonight. Please read the latest Tropical Weather Outlook at www.hurricanes.gov for more details. An Atlantic tropical wave has its axis along 26W, south of 17N, and it is moving W at 20 kt. A 1009 mb low pressure is along the tropical wave axis near 10N26W, or a few hundred nm SSE of the Cabo Verde islands. Scattered moderate to isolated strong convection is noted on the northern semicircle, especially from 10N to 15N and between 24W and 31W. Environmental conditions are expected to remain conducive for development, and a tropical depression is likely to form within the next couple of days. This system is expected to move westward to west-northwestward across the tropical Atlantic during the next several days. This system has a high chance of tropical cyclone formation within 48 hours. Please read the latest Tropical Weather Outlook at www.hurricanes.gov for more details. ...TROPICAL WAVES... Refer to the Special Features section above for details on a tropical wave and associated area of low pressure in the Atlantic Ocean along 24W. In addition, a tropical wave is expected to emerge off of the west coast of Africa toward the end of the week. Environment conditions are forecast to be conducive for development thereafter, while it moves generally west- northwestward over the far eastern Atlantic. An Atlantic tropical wave has its axis along 44W, south of 17N, and moving W at around 10 kt. Scattered moderate convection is noted where the wave meets the monsoon trough from 07N to 12N and between 39W and 48W. A Caribbean Sea tropical storm has its axis along 71W, south of 20N, extending from Hispaniola to W Venezuela, and moving W at around 15 kt. The wave is helping to induce scattered moderate convection over the eastern Caribbean Sea, affecting the waters of the Mona Passage, Puerto Rico and US Virgin Islands. This wave, combined with an upper- level low spinning over Hispaniola, will support showers and thunderstorms over Puerto Rico and Hispaniola today. Another Caribbean Sea tropical wave has its axis along 84W, south of 18N, extending across E Honduras, Nicaragua and Costa Rica into the eastern Pacific Ocean, and it is moving W at around 15 kt. Isolated moderate convection is noted near the northern wave axis in the W Caribbean Sea. ...MONSOON TROUGH/ITCZ... The monsoon trough emerges off the coast of Senegal near 15N16W to the 1009 mb low pressure near 10N26W to 12N35W to 08N48W. The ITCZ continues from 08N48W to the coast of Guayana near 07N58W. Aside from the convection mentioned above, scattered moderate convection is noted well SW of the low center from 07N and between 28W and 36W. GULF OF MEXICO... Refer to the Special Features section above for details on Tropical Depression Nicholas. Tropical Depression Nicholas is centered over SW Louisiana and its tail is causing a line of showers and thunderstorms that extends from SE Louisiana to NE Mexico, with the strongest storms in the area from 23N to 27N and between 92W and 96W. Scattered moderate convection is also noted in the NE Gulf, mainly within 100 nm of the coasts of Alabama and NW Florida. Fairly tranquil weather conditions are present in the rest of the basin. Fresh to locally strong SW-S winds are found in the N Gulf of Mexico, mainly N of 26N and W of 88W, associated with the influence of Nicholas. Seas in the area are 3-6 ft. The rest of the Gulf is experiencing moderate to fresh anticyclonic winds with seas of 1-3 ft. For the forecast, conditions related to the impact of Tropical Depression Nicholas will continue to gradually improve for offshore Louisiana and upper Texas coasts. For the remainder of the week, gentle to moderate mainly southerly flow will dominate the basin. . CARIBBEAN SEA... Refer to the Tropical Waves section above for details on the tropical waves moving across the Caribbean Sea. Moisture in the SW Caribbean Sea associated with the E Pacific monsoon trough results in scattered moderate showers within 60 nm of the coasts of Costa Rica, Panama and NW Colombia. The rest of the basin experiences fairly tranquil weather conditions. The low pressure to the north of the Caribbean is causing a weak pressure gradient across the region, resulting in moderate to fresh trades, with the strongest winds located in the Gulf of Honduras. Seas are 2-4 in the SE Caribbean and Gulf of Honduras, while 1-2 ft seas are found elsewhere. For the forecast, winds will increase to moderate to fresh in the central and eastern Caribbean starting tonight, with locally strong winds possible into the weekend offshore Colombia and in the Gulf of Honduras. ATLANTIC OCEAN... Refer to the Special Features section above for details on the disturbance NE of the Bahamas and the system in the far eastern Atlantic. The 1026 mb subtropical ridge is centered near the Azores and dominates most of the tropical Atlantic. A surface trough is located in the central Atlantic from 30N43W to 25N44W and there are a few showers near the trough axis. Another surface trough is located from 14N33W to 22N34W and it is devoid of any significant convection. The rest of the basin is fairly quiet. Fresh to strong N-NE winds are present off the coast of Mauritania, mainly E of 20W, due to the pressure gradient caused by the ridge and lower pressures over W Africa. This area also experiences seas of 6-9 ft. Gentle to moderate winds and seas of 3-6 ft can be found in the rest of the basin. For the forecast west of 65W, weak high pressure will lead to gentle to moderate mainly easterly winds across the basin. $$ DELGADO