000 AXNT20 KNHC 111629 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1805 UTC Mon Oct 11 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 1620 UTC. ...TROPICAL WAVES... A tropical wave is analyzed near 36W/37W, moving west at 10 kt. A recent scatterometer satellite pass showed a distinct surface trough in this area, as did recent satellite derived winds in the low levels of the atmosphere. A few showers may be active from 04N to 08N between 35W and 39W. This appears to be a fairly shallow feature, and is in a relatively unfavorable upper environment, with strong and dry NW winds aloft. This is limiting convective growth to near the area where the wave interacts with the ITCZ. A tropical wave located along 55W/56W, moving west at 10 to 15 kt. Low pressure with a surface pressure of 1009 mb is centered along the tropical wave near 11N55W or about 350 nm east- southeast of the Windward Islands. The low continues to produce disorganized cloudiness and thunderstorms. Some slow development is possible during the next day or two while the system moves west- northwestward at about 10 to 15 kt toward the Lesser Antilles. After that time, strong upper-level winds are expected to limit further development. Regardless of development, the system could produce locally heavy rainfall and gusty winds across portions of the central and northern Lesser Antilles on Tue, and across the Virgin Islands and Leeward Islands on Wed. Another tropical wave is located over entering the central Caribbean Sea along 69W/70W, moving west at 15 kt. A few showers and thunderstorms are active off southeastern Hispaniola, along the wave axis. This is where the wave is interacting with divergence aloft on the southeast side of a broad upper low centered over the Cay Sal area of the Bahamas. The wave axis shows up well in current satellite derived wind data and 12 UTC sounding data from Santo Domingo and Curacao. A fourth tropical wave is near 84W/85W extending southward through eastern Honduras and eastern Nicaragua, moving west at 15 to 20 kt. This is in an area of deep layer subsidence with strong northerly winds aloft. Other than a few minor showers off Costa Rica associated with trade wind convergence, no significant convection is noted near this tropical wave. ...MONSOON TROUGH/ITCZ... A monsoon trough extends from the mouth of the Gambia River near 13N16W to 06N25W. A segment of the ITCZ continues from 06N25W to 06N33W. Another ITCZ segment reaches from 06N38W to 03N51W. Scattered moderate to isolated strong convection is evident from 04N to 07N between 17W and 22W. Convection elsewhere is described in the Tropical Wave section. ...GULF OF MEXICO... A trough extends from southwest Florida to western Cuba. Another trough is analyzed from near Tampa Bay, Florida to 24N86W. Weak ridging prevails elsewhere across the Gulf. A cluster of thunderstorms is moving off the Texas coast from Galveston Bay to the Sabine Pass and Lake Charles area of Louisiana. Moderate to fresh SE to S winds are noted over the northeast Gulf with 5 to 7 ft seas. Light to gentle E to SE breezes and slight seas are noted elsewhere. For the forecast, the ridge will continue to dominate the Gulf waters during the next several days. Moderate to fresh southerly winds are expected over the western Gulf between the ridge and lower pressure over the Southern Plains and northern Mexico through Thu. Gentle to moderate breezes will persist elsewhere through Fri. ...CARIBBEAN SEA... Regional land-based and buoy observations along with a 12 UTC scatterometer satellite pass confirmed moderate to fresh winds across the far eastern Caribbean, where the pressure gradient is tight between two tropical waves and the Atlantic ridge to the north of the region. Fresh to strong winds and scattered squalls and tstms are possible in the northern Leewards. Based on recent ship and buoy observations and an earlier altimeter satellite pass, seas are 3 to 5 ft in the southeast Caribbean and may be approaching 5 to 7 ft in the northeast Caribbean. Gentle to moderate winds and slight to moderate seas are evident elsewhere across the basin. In addition to the convection extending from the northern Leeward Islands to southeast Hispaniola, modest convection is evident north of eastern Panama near 11N78W. For the forecast, the tropical wave entering the central Caribbean will continue move across Hispaniola and the central Caribbean today. The other tropical wave now located along 55W- 56W is expected to approach the central and northern Lesser Antilles on Tue, and move across the Leeward Islands and Virgin Islands on Wed. Locally heavy rainfall and gusty winds are expected with the wave passage. Northerly swell spreading across the central Atlantic this morning will reach the regional Atlantic waters and Caribbean passages early Tue. ...ATLANTIC OCEAN... A broad upper low centered over the Cay Sal area of the Bahamas is supporting clusters of showers and thunderstorms over much of the northern and central Bahamas, as well as northeast of the Turks and Caicos Islands from 23N to 25N between 68W and 72W. An associated surface trough reaches from 31N78W to a 1011 mb surface low near 27.5N79.5W to the Straits of Florida. Farther east, 1024 mb high pressure is centered near 34N55W. A swath of moderate to fresh SE to S winds extends between the high pressure and the trough from just north of the Leeward Islands to just east of the Bahamas. Buoy observations hint seas may be as high as 8 ft in this area of winds north of Puerto Rico, between 60W and 70W south of 23N. Another upper low is centered near 23N60W with a trough extending southward to near Barbados. Divergence aloft associated with this trough is supporting the convection near the tropical wave along 55W/56W, but is also providing shear and deep layer dry air just to the west of the tropical wave axis. A dying cold front is analyzed from 32N32W to 28N41W then continues as a trough to 28N53W, south of the high pressure. Light to moderate winds are noted north of 25N between 35W and 65W, with moderate fresh trades farther south into the tropics. A a pair of early morning altimeter passes along with recent buoy observations also show evidence of northerly swell with wave heights from 8 to 11 ft north of 25N between 35W and 65W. Seas are 4 to 6 ft elsewhere in open waters east of 35W. East of 35W, scattered showers and thunderstorms are evident just ahead of the cold front north of 27N between 30W and 35W. Light to gentle breezes are evident north of 22N and east of 35W, with mostly moderate trades farther south. A new tropical wave may be emerging off the coast of West Africa, and will be evaluated for the next surface analysis at 18 UTC. The Cumbre Vieja volcano, that is on the island of La Palma in the Canary Islands, has been erupting since 19 September 2021. Currently, significant volcanic ash is seen in the vicinity of the volcano spreading eastward. Marine and aviation interests should monitor this on-going situation, by reading the Volcanic Ash Advisory, that is issued by Meteo- France, at http://vaac.meteo.fr/volcanoes/la- palma/. For the forecast west of 65W, the trough off the east coast of Florida will meander today, then drift eastward and weaken through midweek. Farther south, low pressure is forecast to develop around mid-week near the southeast Bahamas. Northerly swell across the central Atlantic will reach waters east of 72W late tonight through Tue. $$ Christensen