660 AXNT20 KNHC 220004 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 804 PM EDT Fri Sep 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 1800 UTC surface analysis and satellite imagery through 2345 UTC. ...Special Features... Showers and thunderstorms about 360 nm SSE of the Cabo Verde Islands are showing some signs of organization. This activity is associated with a tropical wave, analyzed along 18W from 03N-16N. A recent scatterometer pass shows a partially closed low-level circulation near 07N18W with winds of 25-30 kt in the eastern semicircle. Visible and IR satellite images depict a cluster of convection with a banding pattern from 04N-10N, between 16W-25W, where scattered moderate convection is noted. The environment is forecast to be conducive for slow development, and a tropical depression could form early next week while the system moves west around 15 kt across the low latitudes of the eastern and central tropical Atlantic Ocean. The system has now a medium chance of tropical cyclone formation within the next 48 hours. A central Atlantic tropical wave has its axis along 52W between 07N-17N moving WNW at 08 kt. The wave runs through a 1008 mb low near 13N52W. Shower and thunderstorm activity associated with a these features has become better organized over the past few hours, and a tropical depression could form later tonight or Saturday. Strong upper-level winds and dry air are likely to prevent additional development of this system by late this weekend while it moves west-northwestward to northwestward at around 10 mph. Please refer to the latest Tropical Weather Outlook under AWIPS/WMO headers MIATWOAT/ABNT20 KNHC for more information. ...TROPICAL WAVES... The tropical wave has its axis along 37W been relocated to 36W from 04N-16N and is moving west at 10-15 kt. The wave corresponds nicely with a maximum in TPW imagery. Model analyses depict an associated 700 mb trough along 39W, or just ahead of the wave axis. Isolated showers are noted within 120 nm of the wave axis from 09N-13N. Little change is expected with this wave over the next 24-48 hours. A central Caribbean Sea tropical wave has its axis along 80W. Movement is estimated to be westward around 10-15 kt. Scattered showers are noted west of Jamaica north of 15N between 78W-82W. A maximum in TPW is noted just east of the wave axis. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from the coast of Guinea near 10N14W to 07N18W to 07N27W. The ITCZ continues from 07N27W to 08N40W to 10N56W to NE Venezuela. Other than convection associated with the tropical waves, isolated weak to moderate convection is located within 60 nm south and 150 nm north of the ITCZ between 40W-47W. Scattered moderate convection is also noted over NE Venezuela as well as Trinidad and Tobago. ...DISCUSSION... GULF OF MEXICO... An upper-level cyclonic circulation is moving slowly westward over the far eastern Gulf and the west coast of Florida. Satellite imagery and NWS Doppler Radar indicate scattered showers and thunderstorms over the eastern Gulf, mainly from 24N-29N, between 81W-87W, including portions of the Florida Keys and the Florida Peninsula. A ridge extends from a high pressure over the eastern U.S. to the northern Gulf of Mexico. The ridge will support gentle to moderate easterly winds and seas 3 ft or less across most of the Gulf of Mexico through the middle of next week. It is possible that a typical nocturnal surface trough, that will be moving westward across the southwestern corner of the Gulf of Mexico, may produce locally fresh winds through Sat. CARIBBEAN SEA... A tropical wave is moving across the Central Caribbean Sea. Please see the Tropical Waves section for more details. The eastern Pacific monsoon trough combined with diffluence aloft is helping to induce scattered showers and thunderstorms over portions of Costa Rica, Nicaragua and eastern Honduras. Plenty of moisture will persist over the southwest Caribbean through Saturday as the tropical wave, currently along 80W, reaches the area and moves inland into central America late Sat or early Sun. The pressure gradient between central Atlantic high pressure and the lower pressure near the central Caribbean tropical wave will support fresh trades today. Winds will diminish over most of the Caribbean Sea this weekend. ATLANTIC OCEAN... Currently, there are three tropical waves between the west coast of Africa and the Lesser Antilles. Please see the Special Features/Tropical Waves sections for more details. A cold front extends from a 1011 mb low just SE of Bermuda and enters the forecast area near 31N63W and extends westward to 28N70W to 27N75W. Isolated showers are noted along the frontal boundary. The front will drift slightly southward today, then dissipate by Saturday morning. The low is currently producing moderate to fresh winds north of 28N between 60W-65W. The low is expected to drift south and then west over the forecast area between 60W-70W while weakening. The remainder of the Atlantic forecast area is under the influence of a ridge, anchored by a 1022 mb surface high located near 37N17W. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre/ERA