000 AXNT20 KNHC 182314 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 700 PM EDT Tue Aug 18 2020 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 32N. The following information is based on satellite imagery, weather observations, radar and meteorological analysis. Based on 1800 UTC surface analysis and satellite imagery through 2300 UTC. ...SPECIAL FEATURES... A broad 1009 mb low near 12N38W is moving west at 15-20 kt. This low pressure located about 1300 miles east of the Lesser Antilles is producing a concentrated area of showers and thunderstorms. Environmental conditions are conducive for development, and a there is a high chance a tropical depression is expected to form within the next couple of days while the system moves west-northwestward at 15 to 20 mph across the central and western portions of the tropical Atlantic. Interests in the Lesser Antilles should monitor the progress of this system. Please refer to the latest NHC Tropical Weather Outlook at www.hurricanes.gov for more details. ...TROPICAL WAVES... A tropical wave has its axis along 31W from 02N to 21N, moving westward at about 15 kt. This wave is moving through a moist surrounding environment. Numerous moderate to scattered strong convection is noted from 08N to 15N between 30W and 36W. Over the next day or two, this wave is forecast to approach the low pressure mentioned above in the Special Features section and its associated tropical wave. A tropical wave is analyzed along 47W from 07N to 22N, moving west at 10 to 15 kt. This tropical wave is being enhanced by an upper low to its northwest, near 23N52W, and the relatively sharp axis of the tropical wave shows up well in the low-mid levels of the atmosphere in satellite derived wind flow data. No significant convection is observed in the vicinity of the wave axis. A strong tropical wave is analyzed in the eastern Caribbean along 66W south of 20N, moving west at 20 kt. Numerous moderate to scattered strong convection is seen between 10N and 16N between 64W and 68W. Rich deep layer moisture accompanies the tropical wave, and heavy rainfall has been reported over the Windward Islands over the past 24 hours as the tropical wave moved through the region. Trinidad reported a 24 hour total over three inches of rainfall. A recent scatterometer pass indicated a broad area of fresh NE winds over the northeast Caribbean, mainly south of Puerto Rico. Slightly stronger winds are possible farther south, outside of where the scatterometer sampled. The locally heavy rainfall and gusty winds over portions of the Windward and southern Leeward Islands is gradually subsiding as the tropical wave and main area of moistures shifts westward. This wave is expected to continue moving quickly west over the eastern and central Caribbean Sea during the next couple of days, which is likely to limit significant development. After that time, the system is forecast to move more slowly westward and into the northwest Caribbean, where upper-level winds could become more conducive for the development of a tropical depression during the latter part of this week. The chance of development within the next 48 hours is low, with a moderate chance later in the week. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from the coast of Mauritania, Africa near 18N16W southwestward to 12N32W to the developing low pressure near 11N40W, then on to 09N49W. The intertropical convergence zone continues toward 09N49W to 10N61W. Aside from the convection related to the tropical waves and low pressure described above, scattered moderate convection is observed from 06N to 14N between 37W and 44W. GULF OF MEXICO... A weak, nearly stationary trough reaches from near Panama City Florida to 28N85W, to near Galveston, Texas. The pressure pattern remains fairly weak across the basin, and buoys are showing mostly light to gentle breezes. Seas are 1 to 3 ft in most areas. A few showers are noted within 90 nm of the 1013 mb low that accompanies this trough axis over the central and northwest Gulf, but otherwise no significant showers or thunderstorms are noted. For the forecast, the weak pressure pattern will prevail across the Gulf through Wed night before high pressure over the central Atlantic builds modestly across Florida and into the eastern basin Thu through Fri. Looking ahead, fresh to strong winds are expected over the south central Gulf Sat and Sun with and ahead of a tropical wave and potential low pressure approaching the region from the northwest Caribbean and Cuba. CARIBBEAN SEA... See the Tropical Waves section above for details on the strong tropical wave in the eastern Caribbean. Elsewhere across the basin, scattered moderate showers and thunderstorms are ongoing over the southwest Caribbean, along the coasts of Costa Rica and western Panama, north of the monsoon trough. Scattered moderate convection from afternoon thunderstorms have A few showers and thunderstorms active off Belize earlier this morning have diminished. Seas are estimated to be 5 to 8 ft in the eastern Caribbean due to the fresh to strong winds near the tropical wave. Seas are 3 to 5 ft with moderate to fresh trades in the south central Caribbean, and 1 to 3 ft with light to gentle breezes over the northwest Caribbean. The tropical wave is forecast to move west near 20 kt across the eastern Caribbean Sea. This fast motion should limit development through Wed, but as the wave begins to slow down by late week in the western Caribbean, environmental conditions could become more favorable for the development of a tropical depression. There is a high chance of tropical development Fri through Sun. Looking ahead, low pressure associated with another tropical wave is expected to move across the Tropical N Atlantic waters late Thu and approach the Atlantic waters off the Leeward Islands late Fri. ATLANTIC OCEAN... See Special Features section above for information on the low pressure in the central tropical Atlantic. A weak cold front extends to 31N78W from 1013 mb low pressure north of the area, about 210 nm east of Cape Hatteras. Scattered showers and tstorms are noted about 100 nm southeast of the front. To the west near the Florida coast, afternoon seabreeze has moved Over the eastern coast north of 27N-31N west of 79W. A trough lingers off the central Bahamas, and showers and thunderstorms are noted within 30 nm of 24N68W. Another cluster is evident north of 28N between 60W and 65W. The subtropical ridge is oriented east to west along roughly 28N east of 70W, from 1020 mb high pressure centered near 28N35W. This pattern is allowing generally light winds and moderate seas over the area west of 60W. Moderate to occasionally fresh trades are evident south of this ridge from 15N to 20N over the central Atlantic, with 4 to 6 ft seas. Fresh to strong NE winds are noted off the coasts of Morocco and Western Sahara, where seas are estimated to be 6 to 9 ft. For the forecast, high pressure centered over the central Atlantic extends westward to the NW Bahamas and will dominate this week, bringing gentle to moderate mainly southerly winds north of 23N through Fri. An elongated area of low pressure associated with a tropical wave over the central tropical Atlantic is forecast to move W to WNW this week, and through an environment that is favorable for tropical development. A tropical depression is likely to form in the next few days. This system is forecast to approach the Leeward Islands Fri, move across or just north of the Virgin Islands and Puerto Rico early Sat, and then through the southern Bahamas Sat night. $$ MTorres