129 AXNT20 KNHC 221648 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1248 PM EDT Sun Jul 22 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 1530 UTC. ...TROPICAL WAVES... A tropical wave is off the coast of Africa extending from 09N to 20N along roughly 18N/19N, moving W at 10-15 kt. A large area of Saharan dust is noted along the wave north of 10N. Farther south, scattered moderate convection is noted where the tropical wave intersects the monsoon trough off the coasts of Sierra Leone and Guinea, from 07N to 10N east of 10W. A tropical wave is in the central Atlantic with axis extending from 09N-22N along 41W/42W, moving W at 15-20 kt. This tropical wave continues to be on the leading edge of a large area of Saharan dry air and dust, inhibiting large scale convection at this time. Isolated cells are noted on the southern end of the tropical wave where it intersects the monsoon trough and intertropical convergence zone. A tropical wave is in the western tropical Atlantic with axis extending from 09N-23N along 54W, moving W at 10-15 kt. The tropical wave is accompanied by Saharan dry air and dust, inhibiting large scale convection. However the northern extent of the tropical wave will be coming into phase with a broad upper trough to the northwest of the wave axis. This may allow development of isolated convection later today or tonight approximately 300 nm northeast of the Leeward Islands. A low amplitude and low latitude tropical wave is moving across the Pacific coast plains of Colombia, from 01N-11N along roughly 75W. The tropical wave may be interacting with overnight drainage flow to support a large area of showers and a few thunderstorms off the Pacific coast of Colombia and in the Gulf of Panama. A tropical wave extends from the Gulf of Honduras into the eastern Pacific along roughly 87W. No significant convection is noted in the Caribbean related to this tropical wave. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from the coast of Mauritania near 18N16W to 08N30W. Segments of the intertropical convergence zone reach from 08N30W to the coast of Guyana near 07N59W. Scattered moderate to isolated strong convection is noted from 07N to 10N east of 10W. ...DISCUSSION... GULF OF MEXICO... A surface trough moving across the Florida Big Bend area in the far northeast Gulf may be a focus for a few showers and thunderstorms later today. the northern portion of a tropical wave over the western Yucatan peninsula will move into the southwest Gulf later today, then continue west of the area through Mon. Otherwise, 1017 mb high pressure centered over the west central Gulf near 24N92W is maintaining fair weather, light to gentle winds, and 1 to 3 ft seas. The surface trough over the northeast Gulf will be followed by a weak cold front that will move over the north-central and northeast Gulf waters early this week. This front will become stationary and weaken to a trough by Thu. A surface trough will move off the Yucatan Peninsula into the Bay of Campeche each evening, accompanied by fresh nocturnal winds. Elsewhere, a ridge will prevail. CARIBBEAN SEA... The northern portion of a tropical wave will is moving across the far southwestern Caribbean today, just north of Panama. This may bring increased showers and thunderstorms especially tonight, from the central coast of Panama to Costa Rica. Dry conditions persist elsewhere, and no significant shower or thunderstorm activity is observed. Earlier scatterometer pass indicated fresh to strong trade winds over the south central Caribbean, mainly off Colombia. Maximum seas are estimated to be 8 to 10 ft. Seas are 3 to 5 ft in the northwest Caribbean, and 5 to 7 ft elsewhere. A tropical wave is approaching 55W. While Saharan dry air and dust are inhibiting showers and thunderstorms, there may be isolated showers at least in the Windward Islands by late Mon as the tropical wave moves into the region. Little change is expected elsewhere. ATLANTIC OCEAN... Scattered showers and thunderstorms are ongoing over the northern Bahamas, related to divergent flow aloft. Another cluster of thunderstorms is emerging off the northeast Florida coast, ahead of a deep layer trough moving through the region. Gusty winds are possible with these thunderstorms. A third area of thunderstorms is brewing farther east, about 180 nm northeast of the central Bahamas, in part also related to divergent flow aloft but also related to a weak boundary on the tail end of a weakening front north of the area. Moderate S to SW winds are noted west of 70W with 4 to 6 ft seas in open waters. For the forecast, the Atlantic high pressure along with the low pressure system over the southeast U.S. will continue to produce moderate to fresh southerly winds across the waters just offshore the central and northeast Florida through Wed. Moderate to fresh winds are also expected south of 22N, including approaches to the Windward Passage. Ridging will dominate the area most of the forecast period, with a surface trough reaching the E part of the region by Thu. Farther east, scattered showers and thunderstorms are noted north of 27N between 55W and 65W, related to a broad cold-core mid to upper level low centered near 29N60W. Elsewhere fair weather persist with moderate to fresh NE to E winds and 6 to 8 ft seas north of 20N, and gentle to moderate trades farther south into the tropics with 5 to 7 ft seas. For additional information please visit http://www.hurricanes.gov/marine $$ Christensen