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Tropical Weather Discussion

Tropical Weather Discussion NWS National Hurricane Center Miami FL 1253 AM EDT Thu Jul 19 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 0000 UTC surface analysis and satellite imagery through 0515 UTC. ...SPECIAL FEATURES... SW Caribbean Sea gale warning: A gale is in effect along the coast of Colombia from 11N to 13.5N between 72W and 77W, with seas of 9 to 13 ft. The gale ends on 19/1200 UTC. Please read the High Seas Forecast, under the AWIPS/WMO headers HSFAT2/FZNT02 KNHC, for more details. ...TROPICAL WAVES... A tropical wave is W of the Cabo Verde Islands, with an axis extending from 19N27W to 04N27W, moving westward at 10 to 15 kt. A well defined 700 mb trough near 09N27W is noted in model guidance. A major outbreak of Saharan Air Layer (SAL) dust envelops the wave environment north of 10N as seen in GOES-16 images. As such, satellite imagery shows scattered moderate convection confined south of the SAL from 07N to 11N between 10W and 24W. An E Caribbean tropical wave extends from 22N60W to 05N62W, moving westward at 15 to 20 kt. The wave is depicted on GOES-16 visible and RGB imagery as an inverted-V shape envelope of broken to overcast stratocumulus clouds covering the area. The wave is being intruded upon by Saharan dust limiting significant convection to scattered showers and isolated thunderstorms within 120 nm of either side of the wave. A tropical wave is over the Yucatan Peninsula and Central America from 20N90W to S of SE Mexico at 05N90W, moving westward at 15 to 20 kt. Saharan dust is following in behind this wave axis as observed in GOES-16 satellite imagery. Isolated moderate convection is within 240 nm of the wave axis. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from W Africa near 17N16W to 08N30W to 06N40W, where the ITCZ begins and continues to South America near 05N52W. Aside from convection associated with the tropical waves discussed in the tropical waves section, widely scattered moderate convection is within 120 nm of the ITCZ axis W of 43W. ...DISCUSSION... GULF OF MEXICO... The western periphery of Atlantic high pressure ridging extends E to W over the central gulf waters. Light to moderate anticyclonic flow prevails over the region, outside of thunderstorms. A surface trough extends over the NE Gulf from 30N84W to 28N90W. Current NWS mosaic radar and satellite imagery show scattered thunderstorms over the northern gulf primarily north of 29N E of 91W associated with this surface trough. This activity is also being enhanced by an upper-level trough over and to the NE of the area. The troughing and associated thunderstorm activity is expected to remain over this area for at least the next day or so. Weak high pressure is forecast to prevail across the central gulf waters through Thu night. Thereafter, a frontal trough will cross the NE gulf, forcing the ridge axis farther south over the SE Gulf. Increasing winds are expected over the NE gulf with this frontal trough in the area. Another surface trough will move westward off the Yucatan Peninsula the next few evenings, enhancing nocturnal winds over the eastern half of the SW Gulf. CARIBBEAN SEA... Please read the Special Features section for details about the pulsing gale force winds in the far SW Caribbean near the coast of Colombia. A tropical wave crossing the W Caribbean is discussed in the section above. Elsewhere, low-cloud streamers with brief isolated showers will continue over the far eastern Caribbean through Thu. Scattered showers and thunderstorms are over the interior sections of Hispaniola and Cuba. Mostly fresh E winds will continue over the central Caribbean Sea, and strong NE-E winds will be over the SW and S central sections of the Caribbean, through Sat. ATLANTIC OCEAN... An upper-level trough over the SE United States is helping to enhance shower and thunderstorm activity NW of a line from 31N70W to 27N77W. These thunderstorms will remain active through Thu as a portion of the trough moves off the eastern seaboard. High pressure will build in the wake of this trough late this week. A 1032 mb high well north of the area, centered near 42N37W is dominating much of the central and eastern Atlantic discussion waters. A large area of Saharan Air Layer (SAL) dust is currently over the central Atlantic from 10N to 25N and between 51W and 66W, and over the eastern Atlantic S of 25N E of 51W. The dust will continue to translate westward for the rest of the week. For additional information please visit