000 AXNT20 KNHC 151025 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1205 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 0600 UTC surface analysis and satellite imagery through 1120 UTC. ..SPECIAL FEATURES... Tropical Depression Nicholas is centered near 30.1N 93.8W at 15/0900 UTC or NNE of Port Arthur Texas moving ENE at 5 kt. Estimated minimum central pressure is 1004 mb. Maximum sustained wind speed is 25 kt with gusts to 30 kt. Convection has diminished in association with Nicholas. A slow motion toward the east is expected through Wednesday night, followed by a northward drift on Thursday. Continued gradual weakening is expected during the next day, and Nicholas is forecast to degenerate into a remnant low tonight or early Thursday. Nicholas is expected to produce additional rainfall amounts of 5 to 10 inches across portions of southern and central Louisiana, southern Mississippi, far southern Alabama, and the western Florida Panhandle through early Friday, with isolated storm totals of 20 inches possible from southern Louisiana to the far western Florida Panhandle. Life-threatening flash flooding impacts, especially in urban areas, are possible across these regions. Swells generated by Nicholas affecting portions of the NW Gulf will continue to subside today. The last public advisory has been issued by the National Hurricane Center on this system. Future information on this system can be found in Public Advisories issued by the Weather Prediction Center beginning at 4 AM CDT, under AWIPS header TCPAT4, WMO header WTNT34 KWNH, and on the web at http://www.wpc.ncep.noaa.gov. A far eastern Atlantic tropical wave has an axis along 23W from 19N southward, moving west at 20 kt. A 1009 mb low pressure is along the tropical wave axis near 10.7N23.1W, or a few hundred nm south of the Cabo Verde islands. Showers and thunderstorms associated with this low pressure 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 the system moves generally westward at about 15 mph 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 29N70W to 23N75W reaching the S Central Bahamas. A 1012 mb low pressure is analyzed along the trough axis near 26N71W. This system is producing a large area of disorganized showers and thunderstorms, mainly from 20N-30N between 69W-75W. Environmental conditions appear marginally conducive for gradual development during the next few days, and a tropical depression is likely to 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 27N between 68W and 75W today and tonight. 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. A tropical wave is in the Atlantic Ocean along 42W from 04N to 17N, moving west at around 10 kt. Scattered moderate convection is noted where the wave meets the monsoon trough from 04N to 11N between 40W and 48W. A tropical wave is in the eastern Caribbean Sea along 68W crossing the Mona passage and moving west at around 15 kt. The wave is helping to induce scattered moderate convection over the eastern Caribbean Sea between the Mona Passage, S of Puerto Rico and The U.S. Virgin Islands. The wave combined with an upper-level low spinning over Hispaniola will support showers and thunderstorms over Puerto Rico and Hispaniola today. A tropical wave is in the western Caribbean Sea along 82W from 18N southward near the border of Panama and Costa Rica into the eastern Pacific Ocean, moving west at 15 to 20 kt. Isolated moderate convection is near the wave axis from 12N to 15N. ...MONSOON TROUGH/ITCZ... The monsoon trough emerges off the coast of Senegal near 12N16W to 1009 mb low pressure near 10N24W to 11N34W to 07N47W. The ITCZ continues from 07N47W to 08N58W. Aside from the convection mentioned above, scattered to numerous moderate convection is noted SW of the low center from 01N to 07N between 26W and 31W. GULF OF MEXICO... Refer to the Special Features section above for details on Tropical Depression Nicholas. Middle and high cloudiness prevails over most of the Gulf region and the State of Florida. Isolated showers and thunderstorm are also noted over the Gulf waters. However, showers and thunderstorms are more concentrated west of 90W from 23N to 29N. Gentle to moderate SE-S return flow dominates the basin, except for an area of fresh to strong SW to W winds over the NW Gulf and just S of Nicholas. Seas are in the 2 to 3 ft range east of 87W, and 3 to 6 ft range west of 87W, except 6 to 8 ft in the NW Gulf where the strongest winds are. For the forecast, fresh southerly winds will prevail over the north-central Gulf today in association with the cyclonic circulation of Nicholas. Then, a ridge will build westward across the Gulf waters in the wake of Nicholas producing mainly gentle to moderate SE to S winds the remainder of the week. Fresh easterly winds are expected to the NW of the Yucatan peninsula beginning Fri night due to local effects associated with a thermal trough. 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 thunderstorms over the NE Caribbean, including Puerto Rico and Hispaniola. Abundant mid to upper level clouds cover Cuba, Jamaica and the NW Caribbean. This cloudiness is the result of strong upper level northerly winds. Gentle to moderate trades prevail across the basin, along with seas in the 2 to 4 ft range, except 1 to 2 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 tonight, moderate to fresh winds will develop in the Gulf of Honduras and Gulf of Venezuela and regional waters. Winds will further increase to fresh to strong in the Gulf of Honduras and the south-central Caribbean Thu night, continuing through Sat. Seas are forecast to build to 6-8 ft near the coast of Colombia by Thu night. 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. High pressure dominates the Atlantic forecast waters E of 60W with a 1020 mb high center located near 31N55W. Another high pressure center of 1022 mb is near the Azores. A surface trough remains W of the Cabo Verde islands and extends from 21N32W to 14N33W. Mainly low clouds and limited shower activity is noted near the trough axis. Moderate to fresh winds NE-E winds are noted near the northern end of the trough. An area of fresh to strong northerly winds is E of 20W to the coast of Mauritania due to the pressure gradient between the ridge and lower pressures over W Africa. Gentle to moderate winds dominate the entire rest of basin under the influence of a ridge. For the forecast west of 65W, 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 a trough that reaches the SE Bahamas. $$ Torres