000 AXNT20 KNHC 181711 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 111 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 1200 UTC surface analysis and satellite imagery through 1700 UTC. ...SPECIAL FEATURES... A broad 1009 mb low near 12N38W is moving west at 15-20 kt. This location is about 800 nm WSW of the Cabo Verde Islands. The system is producing numerous moderate to scattered strong convection from 10N to 14N between 33W and 42W. Environmental conditions are conducive for development, and there is a high chance a tropical depression will form within the next day or two. This system may approach the vicinity of the Leeward Islands by Friday or early Saturday. 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 10N to 14N between 30W and 33W. 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 46W from 05N to 23N, 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 fairly well in the lower to 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 65W south of 21N, moving west at 20 kt. Numerous moderate to scattered strong convection is seen between 13N and 15N between 63W and 67W. 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 by earlier this morning. 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 18N19W southwestward to 11N30W to the developing low pressure near 12N38W, then on to 10N45W. The intertropical convergence zone continues toward 10N60W. Aside from the convection related to the tropical waves and low pressure described above, scattered moderate convection is observed from 05N to 07N between 38W and 45W. GULF OF MEXICO... A weak, nearly stationary trough reaches from near Panama City Florida to 28N90W, 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 south of the 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 continue 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 possible Sun over the south central Gulf with and ahead of a tropical wave and potential low pressure approaching the region from the northwest Caribbean and Great Bahama Bank. 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. A few showers and thunderstorms active off Belize ealier 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. For the forecast, in addition to the impacts of the tropical wave currently over the eastern Caribbean as discussed in the Special Features section, low pressure associated with another tropical wave is expected to approach the Atlantic waters off the Leeward Islands Fri or Sat. This may bring gusty winds and a few showers to the far northeast Caribbean then. ATLANTIC OCEAN... See Special Features section above for information on the low pressure in the central tropical Atlantic. A weak cold front extends to 30N78W from 1010 mb low pressure north of the area, about 210 nm east of Cape Hatteras. A few showers are noted along this weak boundary, but they are diminishing. A trough lingers off the central Bahamas, and a small cluster of showers and thunderstorms is 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 west of 60W, the high pressure centered over the central Atlantic will continue to dominate this week, bringing gentle to moderate mainly southerly winds north of 23N. An elongated area of low pressure associated with the tropical wave over the central tropical Atlantic is forecast to move W or WNW this week, and through an environment that is favorable for tropical development. A tropical depression is likely to form in the next day or two. This system is forecast to be northeast of the Leeward Islands Fri or Sat. $$ Christensen