000 AXNT20 KNHC 150006 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 0005 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 1800 UTC surface analysis and satellite imagery through 2000 UTC. ...SPECIAL FEATURES... Tropical Depression Nicholas is centered near 29.9N 94.4W at 14/0000 UTC or 20 nm W of Port Arthur Texas moving ENE at 5 kt. Estimated minimum central pressure is 1003 mb. Maximum sustained wind speed is 30 kt with gusts to 40 kt. Scattered moderate to strong convection is noted over the Gulf of Mexico within 30N93W to 30N84W to 24N90W to 23N96W to 26N97W to 28N93W to 30N93W. Peak seas over the NW Gulf of Mexico are 10 to 11 ft, mainly within the coastal waters between SW Louisiana and eastern coastal Texas. Nicholas will weaken to a tropical depression Wed morning, become a remnant low Thu morning, and dissipate Fri afternoon. By tonight, winds over the waters of the NW and N- central Gulf of Mexico will diminish to 20 kt or less and seas will subside to 8 ft or less. Heavy rainfall through Wed night is likely to cause some flooding across portions of southern and central Louisiana, southern Mississippi and far southern Alabama. Please 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 Nicholas NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov for more details. A far eastern Atlantic tropical wave has an axis along 22W from 01N to 19N, moving west at 20 kt. A 1009 mb low pressure is along the tropical wave axis near 10.5N22W, or a few hundred nm south- southeast of the Cabo Verde Islands. Scattered moderate and isolated strong convection is noted from 10N to 12N between 21W and 24W, from 02N to 07N between 14W and 20W, and from 04N to 10N between 22W and 28W. The associated showers and thunderstorms continue to show signs of organization. Environmental conditions are expected to remain conducive for development, and a tropical depression is likely to form during the next couple of days while system moves generally westward at about 15 kt across the eastern tropical Atlantic Ocean. 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. A surface trough extends from 30N69W to 20N73W near the approach to the Windward Passage, and a couple of hundred nm northeast of the southeastern Bahamas. This is a deep layer trough that extends from the surface to the upper-levels. Scattered moderate and isolated strong convection is noted from 21N to 21N between 62W and 75W. Environmental conditions are forecast to be conducive for gradual development during the next few days, and a tropical depression could form while the system moves north-northwestward to northward across the western Atlantic. This system has a medium chance of tropical cyclone formation during the next 48 hours, and a high chance through the next 5 days. Regardless of development, increased winds and building seas are expected north of 26N between 70W and 75W through Thu. 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 22W. A tropical wave is in the Atlantic Ocean along 40W/41W from 03N to 17N, moving west at around 10 kt. No significant convection is noted with this tropical wave, however scattered showers are noted from 03N to 17N between 38W and 46W. A tropical wave is in the eastern Caribbean Sea along 65W, moving west at around 15 kt. Isolated moderate convection is noted from 13N to 17N between 64W and 69W, with scattered thunderstorms also noted over the U.S. Virgin Islands, Puerto Rico, Hispaniola and the northern coast of Venezuela. A tropical wave is in the western Caribbean Sea along 81W from 18N southward to across western Panama and into the eastern Pacific Ocean, moving west at 15 to 20 kt. Isolated moderate to strong convection is noted from 10N to 14N between 77W and 84W, with additional activity noted over nearby land locations due to afternoon heating. ...MONSOON TROUGH/ITCZ... The monsoon trough emerges off the coast of Senegal near 14N17W to 1009 mb low pressure near 10.5N22W to 13N32W to 08N46W. The ITCZ continues from 08N46W to the NE coast of Venezuela near 9.5N61W. Aside from the convection mentioned above, scattered moderate convection is noted from 10N to 12N between 57W and 59W. GULF OF MEXICO... Refer to the Special Features section above for details on Tropical Storm Nicholas. Otherwise, gentle to moderate SE-S return flow dominates the basin outside of the outer effects of Nicolas. Seas are in the 2 to 4 ft range east of 90W, and 3 to 6 ft range west of 90W outside of the NW and N-central Gulf. For the forecast, Tropical Storm Nicholas will weaken to a tropical depression near 29.8N 94.0W Wed morning. Tropical storm conditions will remain over the SE Texas and SW Louisiana coastal waters through early this evening. Fresh to strong winds will diminish to moderate to fresh tonight and then prevail over the north-central waters through Wed afternoon. For the remainder of the week, gentle to moderate return flow will dominate across the basin. CARIBBEAN SEA... Refer to the Tropical Waves section above for details on the tropical waves moving across the Caribbean Sea. An upper-level low is centered over Hispaniola, enhancing scattered showers and isolated thunderstorms over the north- central Caribbean Sea. Gentle to moderate trades prevail across the basin, along with seas in the 2 to 4 ft range, except 1 to 3 ft over the NW Caribbean Sea. For the forecast, a weak pressure gradient will continue to provide gentle to moderate easterly winds basin-wide. By Wed night, moderate to fresh winds will develop in the Gulf of Honduras and eastern half of the Caribbean. Winds will further increase to fresh to strong in the Gulf of Honduras and the S- central basin Thu night, continuing through Sat. ATLANTIC OCEAN... Refer to the Special Features section above for details on a system in the far eastern tropical Atlantic Ocean that has a high chance of tropical cyclone formation in the next 48 hours, and on the system in the western tropical Atlantic, that has a medium chance of tropical cyclone within the next 48 hours. Elsewhere, a surface trough extends from 22N29W to 13N34W. Another surface trough is from 23N47W to 20N26W. Limited shower activity is noted near the troughs. Moderate to fresh winds are noted west of the eastern trough from 16N to 24N to 35W. Gentle to moderate winds dominate the entire rest of basin due to a weak sub-tropical surface ridge. Seas are in the 3 to 5 ft range west of 35W, and 4 to 6 ft range east of 35W. For the forecast west of 55W, a weak surface ridge will provide mainly gentle to moderate easterly winds, locally fresh over the offshore waters east of the Bahamas due to convection associated with the troughing that extends to the Turks and Caicos. $$ Lewitsky