000 AXNT20 KNHC 201806 TWDAT Tropical Weather Discussion...UPDATED NWS National Hurricane Center Miami FL 1805 UTC Sat Aug 20 2022 Updated to include information from the 1800 UTC Intermediate Advisory for Potential Tropical Cyclone Four, and new scatterometer data in the W Gulf of Mexico 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... Potential Tropical Cyclone Four is centered near 24.1N 96.6W at 20/1800 UTC or 100 nm SSE of mouth of the Rio Grande moving NW at 12 kt. Estimated minimum central pressure is 1010 mb. Maximum sustained wind speed is 30 kt with gusts to 40 kt. Seas are 5-7 ft from 22N to 26N between 94W and 98W, increasing to 7-10 ft from 23N to 25N between 95W and 97W. Scattered moderate convection is noted from 21N to 26N between 93W and 98W. On the forecast track, the current forward motion is expected to continue, bringing the system across northeastern Mexico and southern Texas this evening through early Sunday. The disturbance is expected to produce total rainfall amounts of 1 to 3 inches, with isolated totals of 5 inches, along the eastern coast of Mexico from the northern portions of the state of Veracruz across the state of Tamaulipas to Nuevo Leon through today. Rainfall of 1 to 3 inches will be possible in South Texas through Sunday morning, with continuing uncertainty in how far north and west these amounts will be realized. The potential exists for flash flooding elsewhere along the track of the disturbance. Swells generated by this system are forecast to affect eastern Mexico and southern Texas today and Sunday. These swells are likely to cause life-threatening surf and rip current conditions. The disturbance could still strengthen slightly and become a short-lived tropical storm before reaching the coast of northeastern Mexico. Please consult products from your local weather forecast office. 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 Potential Tropical Cyclone Four NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov for more details. ...TROPICAL WAVES... A tropical wave that moved off the coast of Africa early this morning is now analyzed along 19.5W, from 11N to 23N, with an estimated westward motion of 15-20 kt. Scattered moderate convection, likely enhanced by the Monsoon Trough, is from 11N to 18N between 18W and 24W. This tropical wave has a low chance of tropical cyclone development over the next five days. An eastern Atlantic tropical wave is along 33W, from 21N southward, moving west at 10-15 kt. Scattered moderate convection is from 08N to 10N between 31W and 38W. A central Caribbean tropical wave is along 69W, from 23N southward, moving west at 15-20 kt. The 1200 UTC Upper Air Sounding from Santo Domingo indicated the wave is approaching but has not passed through the city. Scattered showers and tstorms are noted near and over Hispaniola and inland over Venezuela. ...MONSOON TROUGH/ITCZ... A monsoon trough enters the Atlantic at the coast of Mauritania near 18N16W to 13N23W to 09N50W. Aside from the convection described in the Tropical Waves section above, scattered moderate convection is from 08N to 14N between 26W and 31W. GULF OF MEXICO... Please see the SPECIAL FEATURES section for more details on Potential Tropical Cyclone Four. Recent scatterometer data indicates locally strong to near-gale force SSE winds in the NW Gulf associated with several small outflow boundaries propagating away from Potential Tropical Cyclone 4. Outside of the influence of Potential Tropical Cyclone Four, gentle to moderate anticyclonic winds prevail along the western periphery of the Bermuda-Azores High. Seas are 1-3 ft in the E Gulf, and 3-5 ft in the W Gulf north of 25N and south of 22N. For the forecast, Potential Tropical Cyclone Four is near 23.6N 96.4W 1010 mb at 10 AM CDT, moving NW at 11 kt. Maximum sustained winds are 30 kt with gusts to 40 kt. Four may become a brief tropical storm by this evening near 25N 97.5W before making landfall in northeastern Mexico. Four will move inland near 27N99W by early Sun. Seas are forecast to peak near 11 ft with the strongest winds. Heavy squalls associated with this system will continue over the far western Gulf through late tonight or early Sun. Winds and seas will subside early Sun. Weak ridging will prevail over the Gulf early next week, leading to gentle to moderate winds. CARIBBEAN SEA... The Bermuda-Azores High continues to extend ridging into the Caribbean, providing gentle to moderate trades across the basin. Trades are locally fresh in the south-central Caribbean, based on the latest scatterometer pass. Seas are 4-6 ft in the E, Central, and SW Caribbean, and 2-4 ft in the NW Caribbean. Seas are 6-8 ft from 10N to 12N between 75W and 77W, co-located with the aforementioned fresh trades. For the forecast, surface ridging north of the area along with the passage of a tropical wave currently along 70W will continue to support moderate to fresh trade winds in the eastern and central Caribbean through tonight. Fresh to locally strong NE winds are expected across the Windward Passage tonight and Sun night. The ridge will weaken Sun night through Tue, diminishing the winds across the region to gentle to moderate speeds. ATLANTIC OCEAN... The Atlantic remains dominated by the Bermuda-Azores High centered north of the discussion waters. Weak surface troughs are along 54W and 44W, north of 25N. Anticyclonic flow is gentle to moderate across the basin, per this morning's scatterometer data. E to NE winds are fresh on approach to and within the Windward Passage. Seas are 4-6 ft across the Atlantic, as confirmed by satellite altimeter data this morning. However, seas are 6-8 ft south of the Cabo Verde Islands in the E Atlantic, from 07N to 14N east of 27W, in an area of fresh to strong SW winds. For the forecast W of 55W, the subtropical ridge will change little through Sun night, supporting moderate to fresh easterly winds S of 25N through the weekend. Fresh to locally strong winds are likely N of Hispaniola and the approaches of the Windward Passage tonight and Sun night. A weak surface trough will move westward from 65W to 75W Mon and Mon night. The trough will weaken the ridge, thus diminishing winds to gentle to moderate speeds. $$ Mahoney