648 AXNT20 KNHC 250555 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 155 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 0000 UTC surface analysis and satellite imagery through 0445 UTC. ...TROPICAL WAVES... A far eastern Atlantic tropical wave has its axis along is offshore the coast of Africa near 22W from 05N to 20N, moving westward at 15 kt. The wave is in a low to mid-level moist environment as observed in the total precipitable water satellite animation. It is passing to the south of the 700 mb east to west jet stream branch that extends from Africa westward to the eastern Atlantic. Scattered moderate convection is within 120 nm east of the axis from 05N to 07N. A central Atlantic tropical wave has its axis along 49W/50W from 03N-18N, moving westward at 15 kt. The wave is moving through a dry and stable environment which is inhibiting deep convection from developing at this time near it. Only isolated showers are noted within 120 nm either side of the wave axis from 02N to 07N. An eastern Caribbean Sea tropical wave has its axis along 67W/68W south of 18N to well inland S America, moving westward at 10-15 kt. Rather dry and stable conditions depict the surrounding environment of this wave confirmed by the GOES-16 dust depiction imagery. This a result of the Saharan Air Layer (SAL) that is gradually pressing westward across the tropical Atlantic and eastern Caribbean. The wave is void of deep convection. Scattered moderate convection is over S America within 120 nm west of the wave from 05N to 09N. A western Caribbean Sea tropical wave has its axis along 84W/85W south of 19N, moving westward at about 16 kt. Scattered moderate isolated strong convection is over the eastern section of Honduras, and extends northward to 18N and eastward over the Caribbean waters from 15N to 18N. Scattered moderate convection is within 30 nm of a line from 13N81W to 11N83W, and is being mainly enhanced by a mid-level cyclonic circulation that is behind the wave near 11N82.5W. ...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. Scattered strong convection is within 120 nm of the low in the SW quadrant. Scattered moderate convection is within 120 north of the axis between 35W and 38W. Isolated moderate convection is within 60 nm south of the ITCZ between 41W and 42W. ...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. 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 pressure gradient between the central Atlantic high pressure and broad low pressure over the southwestern Caribbean and S America will result will bring fresh to strong trades to the south-central Caribbean waters through early next week. The passage of tropical waves will further tighten the pressure gradient leading to strong to near gale force trades along the coast of Colombia and Venezuela with seas resultant building to around 9 or 10 ft. A tropical wave is forecast to move across the Lesser Antilles Tue night into Wed accompanied by scattered showers and isolated thunderstorms. 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. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre