000 AXNT20 KNHC 141800 TWDAT 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 1700 UTC. ...SPECIAL FEATURES... At 14/1800 UTC, Tropical Storm Nicholas is centered near 29.4N 95.0W, or about 25 nm SE of Houston Texas, and about 10 nm NW of Galveston, moving ENE at 6 kt. Estimated minimum central pressure is 1003 mb. Maximum sustained wind speed is 35 kt with gusts to 45 kt. Scattered moderate to strong convection is within 300 nm of the center in the eastern and southern quadrants, including portions of SE Louisiana and the northwest Gulf of Mexico. Scattered moderate showers are elsewhere within 360 nm of the center in the E semicircle, including over portions of southern Mississippi and the north-central Gulf of Mexico. Peak seas over the northwest Gulf of Mexico are 13 ft as of 14/1200 UTC. The storm should move more slowly toward the east-northeast through tonight, and then turn eastward on Wednesday over Louisiana. Nicholas is forecast to weaken to a tropical depression tonight. By tonight, winds over the waters of the NW and north-central Gulf of Mexico will diminish to 25 kt or less and seas will subside to 8 ft or less. Heavy rainfall through Wednesday 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 20/21W from 03N-18N, moving W at 15 kt. A 1009 mb low pressure is along the wave axis near 10N 20.5W. Scattered moderate convection is seen from 03N-15N between 13W-26W. Associated shower and thunderstorm activity near the low pressure continues to show signs of organization, and environmental conditions are conducive for a tropical depression to form during the next couple of days while the system continues westward. This system has a high chance of tropical cyclone formation within 48 hours. Please see the latest Tropical Weather Outlook at www.hurricanes.gov for more details. A surface trough extends from 20N72W to 28N69W. This is a deep layer trough that extends from the surface to the upper-levels. Scattered moderate and isolated strong convection prevails from 20N-30N between 63W-74W. An area of low pressure is expected to form along the trough during the next day or two a couple of hundred nm north of the southeastern or central Bahamas. Some gradual development of this system is forecast thereafter, and a tropical depression could form later this week while the system moves north-northwestward or northward across the western Atlantic, in between Bermuda and the east coast of the United States. The chance of tropical cyclone formation during the next 48 hours is medium. Regardless of development, increased winds and seas are expected north of 26N between 70W-75W Wed and Thu. ...TROPICAL WAVES... An Atlantic Ocean tropical wave has an axis along 40W from 04N-16N, moving W at 15 kt. Isolated to scattered showers are within 120 nm either side of the wave axis from 06N-15N. An eastern Caribbean Sea tropical wave has its axis along 63/64W, moving W at 15 kt. Isolated moderate convection is noted within 210 nm either side of the wave axis from 13N-20N, including near the northern Leeward and Virgin Islands. The wave combined with an upper-level low spinning over Hispaniola will support showers and thunderstorms over the U.S. Virgin Islands, Puerto Rico and Hispaniola tonight and Wed. Another tropical wave in the Caribbean Sea has an axis along 79W from 19N southward, moving W at 10-15 kt. Scattered moderate and isolated strong convection is observed within 120 nm of the wave axis from 10N-13N. ...MONSOON TROUGH/ITCZ... The monsoon trough emerges off the coast of The Gambia near 13N17W to low pressure 1009 mb near 10N 20.5W to 10N25W, where there is a break in the monsoon trough. The monsoon trough continues from 11N38W to 08N46W. The ITCZ extends from 08N46W to 09N60W. Aside from the convection mentioned above, scattered moderate showers are noted along and within 150 nm N of the ITCZ between 55W-59W. ...GULF OF MEXICO... Tropical Storm Nicholas is weakening, centered near Houston Texas. However, the effects of Nicholas continue to dominate the Gulf of Mexico north of 25N and west of 88W. Nicholas will continue to move inland and weaken to a tropical depression near 30.1N 94.7W this evening. Winds and waves over the northwest Gulf will improve tonight to values of 25 kt or less and 8 ft or less, respectively. Then, moderate to fresh winds will continue over the north-central waters through early Wed evening. See above for more on Nicholas. Moderate SE winds currently prevail over the eastern and southern Gulf of Mexico with seas of 2 to 3 ft. For the remainder of the week, gentle to moderate return flow will dominate across the basin. ...CARIBBEAN SEA... Please see the Tropical Waves section for details on the tropical waves moving across the Caribbean Sea. An upper-level low is centered over Hispaniola, enhancing scattered showers and isolated tstorms over the north-central Caribbean Sea. A recent ASCAT pass shows gentle to moderate trades across the basin. Seas of 2 to 4 ft prevail, except 1 to 3 ft over the NW Caribbean Sea. For the forecast, showers and tstorms will continue near the tropical waves into Wed. Gentle to moderate winds will continue through Wed as a weak pressure gradient remains in place. 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 south-central basin Thu night, continuing through Sat. ...ATLANTIC OCEAN... See the Special Features section above for details on the system in the far eastern tropical Atlantic that has a high chance of tropical cyclone formation, and on the system in the western Atlantic, that has a medium chance of development within the next 48 hours. Elsewhere, a surface trough extends from 12N35W to 22N28W. Another surface trough is from 21N42W to 24N46W. Little to no shower activity and moderate wind speeds are observed near these two troughs. Gentle to moderate winds dominate the entire basin, due to a weak subtropical surface ridge. Seas are 3-5 ft. $$ Hagen