831 AXNT20 KNHC 251205 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 805 AM EDT Sat Aug 25 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 0600 UTC surface analysis and satellite imagery through 1130 UTC. ...TROPICAL WAVES... A far eastern Atlantic Ocean tropical wave is moving across the area of the Cabo Verde Islands, along 24W/25W from 20N southward. Broken to overcast multilayered clouds and possible rainshowers cover the area that is from 14N to 24N between 25W and 37W. A central Atlantic Ocean tropical wave is along 50W/51W from 19N southward. Rainshowers are possible from 14N to 21N between 49W and 61W. An eastern Caribbean Sea tropical wave is along 69W/70W from 18N southward. This wave is moving into an area of pre-existing upper level cyclonic wind flow. Rainshowers are possible within 120 nm on either side of the wave. A western Caribbean Sea tropical wave is along 85W/86W from 20N southward, passing through Honduras, Nicaragua, and Costa Rica. Broad upper level cyclonic wind flow spans the western Caribbean Sea, with upper level cyclonic circulation centers and troughs. Widely scattered to scattered moderate and isolated strong rainshowers are from 20N southward between 77W and 86W. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from the African coast near 15N17W to 08N28W to 09N36W to low pressure at 08N39W 1012 mb. The ITCZ begins at 07N41W and ends just to the east of the wave along 49W/50W. Widely scattered moderate to isolated strong rainshowers from 11N southward from 52W eastward. ...DISCUSSION... GULF OF MEXICO... An inverted upper-level trough over the southeastern gulf is acting on very moist and unstable atmosphere, with the end result bringing scattered showers and isolated thunderstorms to much of that part of the gulf. Similar activity is noted south of 25N between western Cuba and 88W. Scattered moderate convection associated with the nocturnal Yucatan Peninsula trough is weakening over the far eastern Bay of Campeche. Isolated showers and thunderstorms are elsewhere over the area. The pressure gradient across the Gulf supports generally light to gentle east to southeast winds throughout, except for gentle to moderate winds over the far southeast gulf and the northwest gulf and moderate to locally fresh northeast to east winds in the eastern Bay of Campeche into early next week. A surface trough will develop along the western Yucatan Peninsula during the late afternoons, then drift westward during the overnight hours and dissipate along 96W during the late mornings. The trough will support moderate to locally fresh NE to E winds in the eastern Bay of Campeche every night as well as scattered to isolated showers. Surface high pressure, that is to the NE of the region, will support gentle to occasionally moderate SE to E winds across the Gulf of Mexico through Wednesday. CARIBBEAN SEA... Two tropical waves are moving across the basin. Refer to the section above for details. An upper-level low is centered near the Gulf of Honduras at 17N86W. The low is assisting providing additional support to convection associated with the tropical wave along 84W/85W as described above. A mid-level cyclonic circulation is evident in the southwestern part of the sea at 11N82.5W. This feature is entrenched in a very unstable and moisture-laden atmosphere. This has developed scattered moderate convection to the east of the aforementioned wave as described above. This activity is expected to continue to increase through the rest of the morning. The surface pressure gradient between the central Atlantic high pressure and broad low pressure in the southwestern Caribbean Sea and South America will bring fresh to strong winds in the south central Caribbean Sea. The fastest winds will be along the coast of Colombia, increasing to near gale force at night. The sea heights in that region will range from 8 feet to 10 feet. A tropical wave along 86W will continue to support scattered rainshowers, some with thunder, in the NW and SW Caribbean Sea through tonight. A second tropical in the central basin support isolated showers across Hispaniola. A new tropical wave is expected to move across the Lesser Antilles from Tuesday night to Wednesday, bringing rainshowers to the eastern part of the basin. ATLANTIC OCEAN... Two tropical waves are moving across the basin. Refer to the section above for details. A weakening stationary front is off the coast of northern Florida along a position from near 32N78W to just east of NE Florida. A narrow upper-level trough extends along the United States eastern seaboard southwestward to a small upper-level low moving westward at 31N80W to inland NE Florida. Latest satellite and radar imagery shows scattered moderate convection north of 26N between 74W and 80W. An upper-level low is centered east of the Bahamas near 24N75W, and is helping to enhance this convective activity. A western Atlantic surface trough extends from near 26N64W to 20N66W. Scattered showers and isolated thunderstorms are within 60 nm either side of the trough from 23N to 25N, while isolated showers and thunderstorms are elsewhere within 180-210 nm either side of the trough. Another surface trough is analyzed over the central Atlantic from near 31N38W to 25N41W. An upper-level low is located west of the trough near 28N46W. Scattered showers and isolated thunderstorms are seen from 28N to 30N between 42W and 47W. Isolated showers are noted within 120 nm west of the surface trough from 30N to 32N. Saharan dust and associated dry air is noted mainly east of about 64W on the GOES-16 GEO color dust imagery. The dust, although not as dense as in previous weeks, is suppressing convection from developing over much of the central and eastern Atlantic waters, except as described near tropical waves and near the monsoon trough and ITCZ regions. A surface trough, the remnant of a dissipating stationary front, will continue to generate rainshowers, some with thunder, in the waters that are to the N of the Bahamas through Sunday, as the trough moves across Florida into the E Gulf of Mexico. Similar convective precipitation is in the Bahamas and the Great Bahama Bank, being supported by an upper level cyclonic circulation center. A weak surface ridge will prevail elsewhere along with light to gentle variable winds E of the Bahamas, and moderate to fresh E to SE winds W of the islands. The wind speeds will pulse to fresh to strong at night along the N coast of Hispaniola through the middle of the next week. For additional information please visit http://www.hurricanes.gov/marine $$ MT