000 AXNT20 KNHC 171615 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1805 UTC Fri Dec 17 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 1610 UTC. ...MONSOON TROUGH/ITCZ... The monsoon trough is confined to the African continent. The ITCZ begins near the coast of Sierra Leone near 07N13W and continues to 05N27W to 06N40W. A surface trough is west of the ITCZ, extending from 13N39W to 05N42W. Scattered moderate convection is noted off the coasts of Sierra Leone and Liberia, E of 15W. An area of showers and isolated thunderstorms is present south of the ITCZ to 01N and between 30W and 35W. Only a few shallow showers are seen near the surface trough. GULF OF MEXICO... The Gulf of Mexico is in the western periphery of an expansive 1030 mb subtropical ridge located east of Bermuda. Moderate to fresh SE winds prevail in the eastern Gulf, with the highest winds occurring in the Florida Straits. Seas of 2-4 ft are prevalent across the basin, except for seas up to 6 ft in the SE Gulf and Florida Straits. A couple of surface troughs are found in the Gulf, with the most convectively active extending from 29N88W to 25N91W. Divergence aloft is allowing for scattered showers and isolated thunderstorms N of 26N and between 85W and 88W. Fairly tranquil weather conditions and moderate or weaker winds are the norm elsewhere. For the forecast, high pressure north of the Gulf will prevail through Sat, supporting moderate to locally fresh SE to S winds. A cold front is forecast to enter the basin Sat night. Fresh to strong winds and building seas will prevail west of the front on Sun. By Mon, low pressure should develop along the cold front in the central Gulf and steadily progress east-northeastward, pulling the front across the Gulf by Tue. CARIBBEAN SEA... The tight pressure gradient due to an expansive 1030 mb subtropical ridge located east of Bermuda and lower pressures over northern South America result in strong to near gale-force trades across the central Caribbean Sea, with the strongest winds occurring offshore NW Colombia. A recent scatterometer satellite pass show near gale-force trades within 120 nm of NW Colombia. Fresh to localized strong winds are present in the eastern and NW Caribbean, especially in the lee of Cuba. Seas of 6-10 ft are present in the central, SW and eastern Caribbean, with the highest seas occurring offshore NW Colombia. Earlier this morning, an altimeter satellite pass observed 12 ft seas offshore NW Colombia. Moderate or weaker winds and seas of 3-6 ft prevail in the rest of the basin. Low-level convergence continues to enhance the development of scattered showers and isolated thunderstorms in the SW Caribbean Sea, mainly W of 80W. The convection is also affecting eastern parts of Nicaragua and Costa Rica, where localized flooding is possible. A few showers are also noticed in the Gulf of Honduras, affecting the Bay Islands. The remainder of the Caribbean enjoys fairly tranquil weather conditions. For the forecast, a strong Bermuda High will prevail over W Atlantic through Mon. This will support fresh to strong tradewinds over the central and E Caribbean and tropical N Atlantic. Moderate to fresh trades are expected in the W Caribbean through Mon. On Tue, a developing low pressure off of the SE United States coast will act to weaken the tradewinds across the area. Large N swell will reach the tropical N Atlantic zones on Sat and continue through Mon. ATLANTIC OCEAN... An expansive 1030 mb high pressure system positioned to the east of Bermuda dominates the tropical Atlantic, resulting in fairly tranquil weather conditions across most of the basin. A weak cold front extends from 31N27W to 21N50W, where it transitions into a shearline that stretches to 22N65W. Scattered moderate convection is noted within 100 nm to the east of the cold front, mainly N of 29N. The pressure gradient between the strong high and lower pressures in northern South America and the deep tropics result in a large area of fresh to strong NE-E winds, mainly from 10N to 28N and between 40W and the SE Bahamas. The strongest winds are occurring within 175 nm to the north of the shearline. Gales north of the area have generated a large northerly swell which has propagated into much of the tropical Atlantic waters. The swell is producing seas 8-15 ft N of 10N and between 28W and 75W, with seas of 12 ft or greater north of 22N and behind the front to around 63W. A weak surface trough is present to the north of the NW Bahamas, but only a couple of shallow showers are noted near the trough axis. Moderate or weaker winds and seas of 5-8 ft are found elsewhere in the basin. For the forecast, the Bermuda High north of the area is supporting moderate to fresh winds over the forecast waters. The high will build southward, bringing an increase in winds and seas during the weekend. On Mon, a strong cold front will move off of SE United States coast ahead of a developing low pressure on Tue. Large N swell impacting the Atlantic zone from 19N-22N between 55W-65W will diminish on Sun. $$ DELGADO