000 AXNT20 KNHC 091801 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1805 UTC Sat Oct 9 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 1755 UTC. ...SPECIAL FEATURES... An area of low pressure located about 150 miles SE of Wilmington, North Carolina, continues to produce a large area showers and thunderstorms. Scattered moderate convection extends southward to the NW Bahamas and between 72W and 78W. Satellite-derived wind data and surface observations indicate the disturbance is producing a broad area of gale-force winds to the west and north of the center. Associated shower and thunderstorm activity has been gradually increasing and becoming better organized today, and the low could acquire subtropical characteristics late this afternoon through early Sunday. However, by late Sunday and Monday, environmental conditions should become unfavorable for any further development. The low is forecast to move slowly northwestward during the next day or so, and approach the North Carolina coast tonight and early Sunday. Therefore, interests along the North Carolina coast should monitor the progress of this system. Regardless of development, intermittent periods of locally heavy rains and gusty winds will affect southeastern and eastern portions of North Carolina during the next day or two. An Air Force Reserve reconnaissance aircraft is currently investigating the gale area. There is a medium chance of development for this low over the next 48 hours. For more details, please read the latest Tropical Weather Outlook at https://www.hurricanes.gov and Mariners can read the latest High Seas Forecast from the Ocean Prediction Center at https://ocean.weather.gov for more information. ...TROPICAL WAVES... An Atlantic tropical wave has its axis along 45W, south of 18N, and it is moving W at 15 to 20 kt. Recent scatterometer satellite data and satellite imagery depict a well-defined surface trough and wind shift. Fresh to locally strong trades are noted from 09N to 19N and between 37W to 47W. Scattered moderate to isolated strong convection is observed from 05N to 13N and between 33W and 52W. A second Atlantic tropical wave has its axis along 59W, south of 20N, and it is moving W near 15 kt. Recent scatterometer satellite data and satellite imagery show a broad surface curvature and fresh to locally strong trades from 11N to 19N and between 52W and the Lesser Antilles. The wave is interacting with an upper level trough resulting in a large area of showers and isolated thunderstorms, mainly from 11N to 18N and between 53W and 64W, including the Windward Islands. The stormy weather conditions will expand to the rest of the Lesser Antilles later today, affecting the Virgin Islands and Puerto Rico on Sunday and Hispaniola on Monday. A Caribbean tropical wave has its axis along 73W, south of 20N, extending from Haiti to E Colombia, and it is moving W near 15 kt. No deep convection is noted in association with this wave. ...MONSOON TROUGH/ITCZ... The monsoon trough enters the Atlantic Ocean through the coast of Mauritania near 17N16W and continues SW to near 08N24W. The ITCZ extends from 08N24W to 08N35W and to 07N45W. Another segment of the ITCZ extends from 07N47W to 11N58W. Scattered moderate to isolated strong convection is found within 150 nm on either side of the ITCZ and monsoon trough between 27W and the coast of Africa. ...GULF OF MEXICO... A weak 1018 mb high pressure over the Mississippi Valley dominates most of the Gulf of Mexico behind a deep upper level trough that has cleared most of the basin. Dry continental air behind the upper level trough maintains tranquil weather conditions. A couple of surface troughs extending from low pressures off the SE United States are crossing Florida and poking the E Gulf, but no convection are associated with these features. However, atmospheric conditions are favorable for afternoon and evening thunderstorms to develop across South Florida, likely also affecting the surrounding waters. Another surface trough is located in the Bay of Campeche, along 93W and south of 21N. A few showers are observed near the trough axis, but the convection is quickly weakening. The weak pressure gradient allows moderate or weaker easterly winds to prevail. Seas are 1-3 ft in the Gulf. For the forecast, a weak surface ridge will start to build across the basin this evening and moderate to locally fresh return flow will develop over the western half of the basin, continuing through Wed night. ...CARIBBEAN SEA... A tropical wave approaching the Lesser Antilles, previously described in the Tropical Waves section, is producing showers and isolated thunderstorms in the E Caribbean. The E Pacific monsoon trough enters the SW Caribbean through the coast of Costa Rica and extends to the coast of NW Colombia. Scattered moderate convection is noted near the trough axis and within 60 nm of the countries in the region. A weak surface trough in the NW Caribbean extends from 17N to 22N along 84W and is generating a few shallow showers near the trough axis. Recent satellite-based wind data indicate fresh to locally strong trades occurring from 12N to 18N and between 65W and the Lesser Antilles. Fresh trades are also noted within 130 nm of the NW coast of Colombia. Moderate or weaker winds are present elsewhere in the Caribbean. Seas of 3-6 ft are prevalent in the E, central and SW Caribbean, while 1-3 ft prevail elsewhere. For the forecast, the aforementioned tropical wave located E of the Lesser Antilles will provide fresh winds and scattered showers to the Lesser Antilles today through Monday. Shower activity associated with this wave will affect the US/UK Virgin Islands and Puerto Rico Sun evening through the middle of next week and Hispaniola from Mon through Wed night. Seas to 8 ft associated with this wave will affect the Atlantic waters E of the Lesser Antilles through Sun evening. Otherwise, moderate to fresh winds in the eastern half of the Caribbean will diminish to gentle to moderate early on Tue and to light to gentle on Thu. ...ATLANTIC OCEAN... A surface trough extends from 26N59W to 22N71W and it is producing a few showers and isolated thunderstorms near the trough axis. Another surface trough is located from 30N42W to 25N54W and scattered moderate convection is observed near the E extent of the trough axis and north of the tropical Atlantic. The rest of the basin is dominated by a fairly dry weather regime, suppressing the development of showers and thunderstorms. Satellite-derived wind data indicate that fresh to strong southerly winds are found N of 26N and between 36W and 46W. The pressure gradient between the 1031 mb Azores high pressure and lower pressures over NW Africa results in fresh to locally strong NE winds from 18N to 27N and E of 27W. Moderate or weaker winds are found elsewhere in the basin. Seas of 3-6 ft are present W of 60W, while seas of 6-9 ft are found in the rest of the tropical Atlantic, with the highest seas occurring E of the Lesser Antilles and N of the Cabo Verde Islands. The Cumbre Vieja volcano, that is on the island of La Palma in the Canary Islands, has been erupting since 19 September 2021. Currently, volcanic ash is not easily detectable due to cloud cover. 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, a well-defined, non-tropical low pressure system located about 175 nmi SE of Morehead City and Wilmington, North Carolina, continues to produce a large area of cloudiness and disorganized showers and thunderstorms over the offshore waters N of the Bahamas. Environmental conditions could briefly become marginally conducive for the low to acquire subtropical characteristics through early Sunday. The low is forecast to move slowly NW during the next day or so, and approach the North Carolina coast tonight and early Sunday. Regardless of development, a trough extending from the low will continue to generate showers over the SW N Atlc waters through Mon. $$ DELGADO