000 AXNT20 KNHC 112112 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 0005 UTC Tue Oct 12 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 1800 UTC surface analysis and satellite imagery through 2100 UTC. ...TROPICAL WAVES... A tropical wave was added to the analysis off the coast of West Africa along 18W/19W. Scattered moderate convection is observed from 03N to 08N between 17W and 22W. A tropical wave is analyzed near 37W/38W, moving west at 10 kt. An earlier scatterometer satellite pass showed a distinct surface trough in this area. A few showers may be active from 05N to 09N between 37W and 40W. This is 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 57W/58W, moving west at 10 to 15 kt. 1010 mb low pressure is centered along the tropical wave near 13N57W or about 180 nm east of Barbados. Recent satellite-derived wind data indicate that the system has not developed a well- defined center. The potential for development of this system has decreased, and strong upper-level winds should prohibit further development on Tue. Regardless of development, the system could produce locally heavy rainfall and gusty winds across portions of the central and northern Lesser Antilles on Tue. Another tropical wave is located over entering the central Caribbean Sea along 70W/71W, moving west at 15 kt. A few showers and thunderstorms are active from the northern Leeward Islands to the eastern Dominican Republic, east of 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. A fifth tropical wave is near 86W extending southward through Honduras and central Nicaragua, moving west at 15 to 20 kt. This is in an area of deep layer subsidence with strong northerly winds aloft and, 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 07N25W to 07N30W. A segment of the ITCZ continues from 06N30W to 07N37W. Another ITCZ segment reaches from 07N40W to 07N50W. No significant convection is observed other than what is described in the Tropical Wave section. ...GULF OF MEXICO... A trough extends from southwest Florida along the Lower Florida Keys to the southeast Gulf near 24N84W. Another trough extends from near Clearwater, Florida to 23N86W. 1015 mb high pressure centered near 27N88W dominates the remainder of the Gulf. No significant shower or thunderstorm activity is evident. Moderate to locally fresh SE winds are noted over the western Gulf, between the high pressure and lower pressure over northeast Mexico. Seas over the western Gulf are 4 to 6 ft. 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 into mid week over the western Gulf between the ridge and lower pressure over the Southern Plains and northern Mexico. Looking ahead, these winds may increase slightly Thu before diminishing Fri ahead of a cold front expected to move into the northwest Gulf Fri night. Strong northerly winds and building seas are possible Sat. Gentle to moderate breezes will persist elsewhere through Sat. ...CARIBBEAN SEA... Regional land-based and buoy observations along with an earlier scatterometer satellite pass confirm moderate to fresh winds persist 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 4 to 6 ft in the eastern 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, a few showers are evident from 13N to 15N between 65W and 68W. For the forecast, conditions will improve across the NE Caribbean tonight as the wave moves W and gradually weakens. Another tropical wave along 56W-57W is expected to approach the central and northern Lesser Antilles early Tue, and move across the Leeward Islands and Virgin Islands Tue afternoon through Tue night. Expect similar active weather and strong gusty winds with the wave passage. Northerly swell spreading across the central Atlantic today will reach the regional Atlc waters and Caribbean passages early Tue. ...ATLANTIC OCEAN... A broad upper low centered over the Cay Sal area of the Bahamas continues to support clusters of showers and thunderstorms over much of the northern and central Bahamas, as well as over central Cuba and southeast Florida. Additional showers and thunderstorms are active northeast of the Turks and Caicos Islands from 23N to 25N between 68W and 71W. An associated surface trough reaches along the coast of southeast Florida 29N80W to 1011 mb low pressure near 26N80W to 23N86W in the southeast Gulf of Mexico. Farther east, 1023 mb high pressure is centered near 34N53W. 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 56W/57W, but is also providing shear and deep layer dry air just to the west of the tropical wave axis. A trough is analyzed from 32N31W to 26N47W. Light to moderate winds are noted north of 25N between 35W and 65W, with moderate fresh trades farther south into the tropics. Recent altimeter passes and 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. 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. Northerly swell across the central Atlantic will reach waters east of 72W late tonight through Tue. Low pressure may form over the southeast Bahamas by Wed. Regardless of development, locally heavy rainfall may persist over portions of the Leeward Islands, Puerto Rico, and Hispaniola during the next couple of days. $$ Christensen