116 AXNT20 KNHC 211803 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 203 PM EDT Tue Aug 21 2018 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 1745 UTC. ...TROPICAL WAVES... A tropical wave is just inland to just offshore the coast of Africa with its axis near 17W, moving westward at 10-15 kt. The wave is embedded within a very dry and stable environment. Only isolated moderate convection is occurring within 180 nm east of the wave axis from 11N to 14N. A central Atlantic tropical wave has its axis extending from 05N37W to 13N38W to 19N37W, moving westward at 10-15 kt. This wave is also embedded within a very dry and stable environment caused by Saharan Air Layer outbreak migrating westward across the central and eastern Atlantic. Only isolated moderate convection is noted within 60 nm either side of the wave axis from 10N to 11.5N. A tropical wave over the eastern Caribbean has its axis from well inland Venezuela north-northeastward to 15N65W and to the proximity of the Virgin Islands. It is moving westward near 16 kt. Scattered moderate convection trails the wave from 09N to 11N east to near 58W. A western Caribbean tropical wave has its axis extending along 85W/86W and south of 21N, moving westward near 15 kt. Only isolated showers and thunderstorms are noted within 60 nm east of the wave. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from coast of Senegal near 14N16W to 10N23W to 09N31W and to 09N41W, where latest scatterometer data indicates that the ITCZ axis begins and continues to 09N50W to 09N60W. No significant convection is noted. Only isolated showers and thunderstorms are seen within 120 nm north of axis between 43W and 48W. ...DISCUSSION... GULF OF MEXICO... Weak ridging reaches across the northern Gulf of Mexico along roughly 27N, maintaining light to gentle breezes and 1 to 3 ft seas. Gentle to moderate easterly flow is noted elsewhere south of the ridge. Latest NWS mosaic radar display shows isolated showers and thunderstorms across much of the eastern part of the gulf, mainly due to a weak trough over that area. Scattered showers and thunderstorms are observed over the far southwest section of the gulf in association with the Yucatan Peninsula trough that typically moves offshore across the southwestern gulf late at night and into the morning hours, with the added factor of an upper-level low located just east of the coast of Mexico at 22N97W. Expect for this convective activity to remain active through tonight. Otherwise, high pressure ridging will remain across the northern gulf waters, with the associated gradient producing gentle to moderate anticyclonic flow through Thu. CARIBBEAN SEA... The pressure gradient across the area will maintain fresh to strong winds over the south central Caribbean off the coast of Colombia and across the Gulf of Venezuela through Thu. Moderate to fresh trades will continue elsewhere through Thu. The tropical wave along 85W/86W will move across the rest of the western Caribbean this evening before moving inland Central America. The tropical wave along 65W will move across the rest of the eastern Caribbean through Wed night and enter the eastern part of the central Caribbean Thu. ATLANTIC OCEAN... Over the western Atlantic, a surface trough is analyzed from near 30N74W to the central Bahamas. An upper-level trough extends from an upper-level low at 31N66W to the central Bahamas, and to central Cuba as a shear axis. Another trough extends from 32N59W to 27N68W, and another one extends from near 32N45W to 28N50W. A small surface trough extends from near 31N54W to 28N56W. With these features in place along with a moist and unstable environment, the result is scattered shower and thunderstorm activity over the waters north of 24N between 60W and 75W, with the most concentrated activity observed north of 27N and between 70W and 76W. Isolated showers and thunderstorms are elsewhere west of 58W. A 1025 mb high center is analyzed north of these troughs at 32.5N59W, with a ridge extending westward to Bermuda, and southwestward from there to east-central Florida High pressure ridging will continue over the basin through the next several days. The trough extending across the central Bahamas will continue westward through this evening. The aforementioned shower and thunderstorm activity is forecast to persist through Wed. Over the eastern part of the basin, a 1028 mb high is centered near 34N42W, supporting generally moderate north to northeast winds north of 20N. Saharan dust and associated dry air, as also mentioned above under Tropical Waves, is noted mainly east of about 56W on GOES-16 Saharan Air Layer animation is inhibiting convection from developing across the eastern and central Atlantic waters. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre