516 AXNT20 KNHC 211756 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 156 PM EDT Sat Jul 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 1500 UTC. ...TROPICAL WAVES... A tropical wave is starting to move off the coast of Africa this afternoon, accompanied by thunderstorms from Sierra Leone to Senegal. A tropical wave is in the eastern Atlantic with axis extending from 05N-22N along 32W, moving W at 10-15 kt. Saharan dry air and dust continue to prevail in the wave's environment as shown by CIRA LPW and GOES-16 RGB imagery. This is inhibiting large scale convection at this time, although isolated showers are noted where the tropical wave intersects the monsoon trough. A tropical wave is in the central Atlantic with axis extending from 05N-21N along 48W, moving W at 10-15 kt. The wave is moving across an extensive area of Saharan dry air, which is hindering convection at the time. A low amplitude and low latitude tropical wave is moving across Venezuela into eastern Colombia with axis extending from 00N-10N along 67W, moving W at 10-15 kt. Numerous moderate to isolated convection is observed across the Orinoco Plains of eastern Colombia. The tropical wave will lose some definition as it moves across the Andes through Sun, but may emerge into the eastern Pacific off Colombia Mon. A tropical wave is in the west-central Caribbean from western Panama to central Cuba. The tropical wave is interacting with trade convergence to support thunderstorms from central Panama to off Costa Rica to eastern Nicaragua. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from the coast of Mauritania in W Africa near 18N15W and continues to 10N25W to 09N40W. The ITCZ begins near 09N40W and continues to Guyana near 08N60W. Scattered moderate convection is noted from 07N to 09N between 28W and 32W. ...DISCUSSION... GULF OF MEXICO... A vigorous short wave trough in the mid to upper levels of the atmosphere is supporting a large area of thunderstorms moving through southwest Georgia and the eastern Florida Panhandle. The storms will move across the Florida Big Bend area of the far northeast Gulf over the next two to three hours, catching up to a surface trough moving south into central Florida and the east central Gulf. Farther south, a few thunderstorms remain active approximately 120 nm southwest of Tampa Bay. Buoy observations and recent scatterometer data show moderate to fresh W to NW winds over the northeast Gulf, with 2 to 4 ft seas. Stronger gusts and locally higher seas are possible near the thunderstorms emerging into the Big Bend area. Elsewhere, 1017 mb high pressure is centered over the south central Gulf with a surface ridge extending toward the Texas coast. This is maintaining gentle breezes and 1 to 3 ft seas. The weak boundary across Central Florida will gradually settle southward over the next few days, bringing moderate west- southwesterly flow. The increasing westerly fetch will bring gradually higher seas in the offshore Gulf waters by early next week. Showers and thunderstorms will persist over the eastern Gulf through Sun. A surface trough will move off the Yucatan Peninsula into the Bay of Campeche each evening, accompanied by fresh nocturnal winds and scattered showers. Otherwise little change is expected. CARIBBEAN SEA... A scatterometer pass from 14 UTC showed strong to near-gale force trade winds of the central and northeast coasts of Colombia, reaching as far north as 15N. Seas are estimated to be 10 to 13 ft in this area. Aside from the thunderstorms over the southwest Caribbean, little to no shower or thunderstorm activity is noted due to the presence of Saharan dust and dry air, mainly impacting the eastern Caribbean. For the forecast, high pressure north of the area will support strong to near gale force winds in the south-central Caribbean through tonight before winds diminish. ATLANTIC OCEAN... Mid to upper-level diffluent flow between a ridge in the west Atlantic and a trough along the eastern U.S. continue to support scattered showers and tstms in a line from roughly Grand Bahama to north of 31N75W. Similarly divergent flow aloft between the upper ridge and an upper low farther east near 28N57W will support scattered showers and thunderstorms northeast of the Turks and Caicos Islands within 90 nm of of 24N69W. Saharan dust is evident to the south of this clusters of thunderstorms, presenting the potential for strong gusty winds accompanying these thunderstorms. For the forecast, high pressure ridge across the northern waters will remain in place through Sun before lifting N Mon through Wed. Scattered showers and thunderstorms will persist N of 27N and E of 78W through early next week. Fair weather is elsewhere across the Atlantic, however hazy conditions are expected S of 26N as the extensive Saharan Air Layer outbreak moves across the Atlantic tropical waters. For additional information please visit http://www.hurricanes.gov/marine $$ Christensen