000 AXNT20 KNHC 201646 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1246 PM EDT Wed Jun 20 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 1715 UTC. ...TROPICAL WAVES... There are four tropical waves between the west coast of Africa and the Lesser Antilles. A tropical wave is added to the 1200 UTC analysis/surface map along 18W from 03N-11N. The Hovmoller Diagram shows the westward propagation of the wave, that coincides with a modest surge of moistened air based on the TPW product. A cluster of moderate convection's just ahead of the wave's axis from 5N-8N between 18W-21W. A tropical wave is along 27W from 3N-11N, moving W at 20 knots. This wave shows up well as a low amplitude moisture surge on the TPW animation. Scattered moderate convection is noted where the wave meets the ITCZ. A tropical wave is along 38W from 3N-11N, moving W at about 15 knots. African dust surrounds the wave limiting convection. the wave is well depicted in the moisture product. Scattered moderate convection is also noted where the wave meets the ITCZ. Another tropical wave is along 55W/56W from 5N-14N, moving W at about 10 knots. The TPW animation shows a surge of moistened air near the wave's axis. A cluster of moderate convection is along the wave's axis from 9.5N-11.5N between 55W-57W. Moisture associated with this wave will reach the Windward Islands by Thu morning. The wave will move across the eastern Caribbean Thu afternoon through Fri night. The associated moisture is forecast by the GFS computer model to spread out reaching Puerto Rico on Fri. A tropical wave is moving across the eastern Caribbean. Its axis is along 69W, and extends from eastern Dominican Republic to the coast of Venezuela. The wave combined with an upper-level trough crossing eastern Cuba is producing scattered showers and tstms from eastern Dominican Republic to the Virgin Islands, including the Mona Passage. Lingering moisture from this tropical wave will continue to support showers and isolated thunderstorms across most of Puerto Rico today. Moisture and instability related to this wave will affect Hispaniola today and Thu, reaching eastern Cuba by late Thu. ...MONSOON TROUGH/ITCZ... The monsoon trough passes through the coastal sections of Sierra Leone near 08N13W to 06N26W. The ITCZ continues from 06N26W to 05N40W to 04N48W to 07N55W. Scattered moderate convection is roughly noted from 3N-7N between 18W-40W. ...DISCUSSION... GULF OF MEXICO... A 1005 mb low pressure centered inland in the Deep South of Texas near 27N98W continues to produce a large area of showers and tstms over the western Gulf coast. Similar convective activity is flared up over the west-central Gulf, particularly N of 21N W of 95W. This slow moving system will continue to deliver heavy rainfall and flooding along the coast of Texas into Louisiana. A widespread 3 to 5 inches of rainfall is possible over this region through Thu morning with isolated pockets of heavier amounts expected. A 1016 mb high pressure is analyzed over the eastern Gulf near 27N86W. The pressure gradient between the high pressure and the low over southern Texas will support fresh SE winds in the NW Gulf through this evening. Abundant tropical moisture will persist from Texas to Florida across the northern Gulf through late Thu. A typical pattern, with a ridge, and a surface trough developing over the Yucatan Peninsula each afternoon, then moving westward across the SW Gulf during overnight hours, accompanied by fresh east to southeast winds, is expected to persist Thu through the weekend. CARIBBEAN SEA... A tropical wave is moving across the eastern Caribbean. Another tropical wave is forecast to reach the Windward Islands by Thu morning. Please, see Tropical Waves section for details. Expect increasing showers and isolated thunderstorms in association with the passage of these waves. High pressure N of area is forecast to strengthen over the next couple of days while moving westward. As a result, the trade winds across the south-central Caribbean will strengthen on Thursday, then expand in coverage across the basin this weekend. Strong winds will affect the Gulf of Honduras tonight, then return Fri night through Sun night. An upper-level trough extends from a cyclonic circulation located over the western Atlantic near 27N65W to another cyclonic circulation over the NW Caribbean. This feature is a TUTT (Tropical Upper-Tropospheric Trough) that extends from the Atlantic into the Caribbean during May to October. They are cold- core systems that exist mostly above 500 hPa. They are sources of clouds and precipitation. Currently, a SW flow on the SE side of this upper-level trough that also crosses eastern Cuba is helping to induce some shower and thunderstorm activity over the coast of Nicaragua and regional waters, just S of Hispaniola, and over Puerto Rico and the Virgin Islands. ATLANTIC OCEAN... As previously mentioned, an upper-level trough extends from a cyclonic circulation centered near 27N65W to eastern Cuba. A surface trough is analyzed from 28N60W to 27N70W to the NW Bahamas. Scattered showers and tstms are noted S of the trough to about 20N between 60W and 70W. A diffluent pattern aloft between the upper-level trough and an anticyclonic circulation located E of the Lesser Antilles is helping to induce this convective activity. A ridge dominates the remainder of the Atlantic Ocean with a 1028 mb high pressure situated near 34N30W. This system will build westward over the region through Thu, bringing mainly fresh trades across the Tropical N Atlantic waters, particularly S of 19N W of 45W Fri night through Sun. A weak trough is expected to move into the northwest waters Fri through Sat night, with little effect. For additional information please visit http://www.hurricanes.gov/marine $$ GR