154 AXNT20 KNHC 210003 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 0005 UTC Sun Nov 21 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 2345 UTC. ...MONSOON TROUGH/ITCZ... The monsoon trough passes through the coastal plains of Guinea near 11N15W and continues to 07N21W, where latest scatterometer data indicates that it transitions to the ITCZ continuing to 07N29W to 04N35W and to 04N46W. Scattered moderate convection is seen from 01N to 07N between 20W-29W, from 07N to 14N between 26W-32W and within 120 nm north of the ITCZ between 32W-35W. GULF OF MEXICO... As of 21Z, a cold front is analyzed from near Fort Myers, Florida to 24N86W, where it becomes a trough to inland the western section of the Yucatan Peninsula and continues to southeastern Mexico to the northern sections of the Isthmus of Tehuantepec. Satellite imagery shows broken to overcast multilayer clouds, with scattered showers and thunderstorms along and to between 60-90 nm northwest of the trough. Isolated showers and thunderstorms are southeast of the trough. Elsewhere to the northwest of the front and trough, strong subsidence aloft as noted in water vapor imagery, is inhibiting convection from developing there. At the surface, a ridge extends from western Louisiana to the interior of Mexico, where high pressure of 1023 mb is analyzed near 22N102W. Latest ASCAT data shows moderate to fresh northeast to east winds over the eastern and central Gulf, while gentle to moderate east-southeast winds are over the western half of the Gulf. Seas are in the 5-7 ft range over the NE Gulf, 4-6 ft over the central Gulf, 6-9 ft over the SW Gulf due to a northeast swell and lower seas of 2-4 ft over the NW Gulf. As for the forecast, the aforementioned front will gradually dissipate tonight and Sun as high pressure builds across the region. A strong cold strong will make its way into the basin by early Mon. Fresh to strong northerly wind will be expected behind the front, mainly over the eastern Gulf, Mon through Tue night. High pressure is forecast to build in behind the front by middle of the upcoming week. CARIBBEAN SEA... A surface trough is analyzed along 64W from 15N to 19N. The eastern segment of the E Pacific monsoon trough reaches from northern Panama to inland the northwest coast of Colombia near 11N74W. Latest ASCAT data indicates a northeast to southeast wind shift across the axis. These winds are of gentle to moderate speeds. No convection is noted with this trough as it remains under subsidence aloft that is allowing for very dry and stable atmospheric conditions to exist over the eastern and central section of the basin. Isolated showers moving quickly westward are possible north of 14N between 63W and 67W, and between 76W- 80W. In contrast to the eastern and central Caribbean sections, deep atmospheric moisture aided by a subtropical jet stream branch covers just about the entire western half of the basin. Scattered showers and a few thunderstorms are noted south of 16N between 80W and the coast of Central America. Small isolated showers are north of 16N and west of 80W. The latest scatterometer data shows moderate to fresh trades south of about 16N and between 71W and 80W. The data also shows gentle to moderate trades elsewhere over the remainder of the sea, except for mainly gentle winds over the western section of the sea and near the Windward Passage. Seas are in the 3-5 ft range, except for slightly lower seas of 2-4 ft north of 15N and between 64W and 85W. As for the forecast, mainly gentle to moderate trades will prevail across much of the Caribbean Sea through Sun night. A cold front is forecast to reach the Yucatan Channel by Mon evening, and extend from eastern Cuba to the Gulf of Honduras by Tue evening. Fresh to locally strong winds and building seas are expected behind the front across the western Caribbean, the Windward Passage and Mona Passage. ATLANTIC OCEAN... A cold front stretches from just east of Bermuda southwestward to 31N67W and to 28N75W, where it becomes weaker to inland South Florida near West Palm Beach and southwest from there to near Fort Myers. Fresh to strong northeast to east winds are north of this front. A surface trough is over the Bahamas along 78W. It reaches south to the coast of Cuba. Ample deep atmospheric moisture acted upon by jet stream energy from a subtropical jet stream branch that extends from the southeastern Gulf of Mexico northeastward to east of northern Florida is resulting in numerous to scattered showers and isolated thunderstorms south of the cold front and west of 65W. Some of this activity may contain strong gusty winds and heavy rain that can reduce visibility. Over the eastern part of the area, a broad upper-level trough is located north of about 19N and between 20W and 50W, This feature is sustaining a cold front that extends from a 1001 mb low that is north of the area near 36N33W, southwestward to 31N29N and to 24N37W, where it begins to dissipate to near 21N49W. Satellite imagery reveals isolated showers along and near this front. Latest scatterometer data passes show moderate to fresh northwest to north winds behind the front east of 40W, and mainly moderate northeast to east winds elsewhere behind the front. Moderate winds or lighter are elsewhere over the area. Seas are in the 7-11 ft range behind both fronts, mainly due to swell, and 4-7 ft elsewhere, except for seas of 6-8 ft due to a north to northeast swell from 22N to 27N between 70W and the Bahamas. The Cumbre Vieja volcano, on the island of La Palma in the Canary Islands, has been erupting since 19 September 2021. Medium ash is in the vicinity of the volcano, while low concentration is elsewhere. Marine and aviation interests should monitor this ongoing situation by reading the Volcanic Ash Advisory issued by Meteo-France, at http://vaac.meteo.fr/volcanoes /la-palma/. For the forecast W of 65W, the weakening aforementioned cold front will stall and remain across the northern forecast waters through Sun night, before lifting north ahead of a strong cold front that will move off the northeast Florida coast on Mon. Before this occurs, strong high pressure is building offshore the southeastern United States creating a tight pressure gradient over the western part of the area. This is expected to lead to strong northeast to east winds over a large oceanic fetch area resulting in hazardous marine conditions through late Sun, with large swells possibly lingering into Mon. $$ Aguirre