National Hurricane Center's Tropical Weather Discussion

North America - Central America - Gulf of Mexico - Caribbean - Atlantic Ocean

810 AXNT20 KNHC 211735 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 135 PM EDT Thu Jun 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 1200 UTC surface analysis and satellite imagery through 1715 UTC. ...TROPICAL WAVES... As of 1200 UTC, there are four tropical waves between the west coast of Africa and the Lesser Antilles. A tropical wave is along 25W from 03N-12N, moving W at 20 kt. The Hovmoller Diagram shows the westward propagation of the wave, that coincides with a modest surge of moistened air based on the TPW product. Abundant cloudiness surrounds the wave's axis but convection is limited. A tropical wave is along 34W from 3N-11N, moving W at 20 kt. This wave shows up well as a low amplitude moisture surge on the TPW animation. Scattered showers are noted where the wave meets the ITCZ. A tropical wave is along 43W from 3N-11N, moving W at about 15 knots. The wave is well depicted in the moisture product, and model diagnostics guidance. Scattered moderate convection is noted on either side of the wave's axis from 6N-8N between 40W- 46W. Another tropical wave is along 60W from 6N-17N, moving W at about 10 knots. The wave coincides with a high amplitude northward bulge of moisture, and is also well depicted in model diagnostics guidance. Scattered moderate convection is already affecting Trinidad and Tobago as well as Barbados, where showers and some tstms have been reported. Moisture associated with this feature will continue to affect the Windward Islands today. The wave will then move across the eastern Caribbean this afternoon through Fri night. The associated moisture is forecast by the GFS computer model to spread out reaching the Leeward Islands later today and tonight, and Puerto Rico on Fri, then Dominican Republic Fri night into Sat. A tropical wave is moving across the Caribbean Sea. Its axis is along 73W, and extends from Hispaniola to northern Colombia. The wave is interacting with an upper-level trough that crosses eastern Cuba. Lingering moisture from this tropical wave will continue to support scattered showers and isolated thunderstorms across Hispaniola today. Moisture and instability related to this wave will also affect the Windward Passage and eastern Cuba, as well as Jamaica today. Currently, scattered showers and tstms are noted in the Windward Passage, across the waters between eastern Cuba and Jamaica, and E of Jamaica. This wave is forecast to move across Jamaica tonight, entering the western Caribbean Fri. ...MONSOON TROUGH/ITCZ... The monsoon trough passes through the coastal sections of Guinea near 10N13W to 06N29W. The ITCZ continues from 06N29W to 06N30W 05N40W to 05N50W to 06N57W. Outside of the convection associated with the tropical waves, isolated moderate convection is from 3N- 7N between 24W-35W. Scattered moderate convection is from 6N-8N between 55W-58W. ...DISCUSSION... GULF OF MEXICO... A 1007 mb low pressure centered along the Texas/NE Mexico border near 27N99W continues to produce a large area of showers with embedded tstms over the western Gulf coast and NE Mexico, particularly over the states of Nuevo Leon and Tamaulipas, where heavy rain has been reported. This slow moving system will continue to generate rounds of rainfall across the western Gulf coast from Texas to western Louisiana today. Flooding of low lying and poor drainage areas will be possible. Winds and seas in the NW Gulf will diminish further today as the low weakens. A 1016 mb high pressure is analyzed over the SE Gulf near 24N86W. A broad ridge will persist over this area, and support light winds and seas less than 3 ft east of 88W through the upcoming weekend. A surface trough will develop in the Yucatan Peninsula each afternoon, then move westward across the SW Gulf during the overnight hours, accompanied by fresh to occasionally strong east to southeast winds. CARIBBEAN SEA... A tropical wave is moving across the central Caribbean. Another tropical wave has reached the Windward Islands. Wind observations from these islands clearly show the wind shift associated with the wave's axis. Please, see Tropical Waves section for details. Expect increasing showers and isolated thunderstorms in association with the passage of these tropical 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 over the south-central Caribbean will strengthen and expand in areal coverage across the basin through early next week. Winds could reach near gale force along the coast of Colombia by Sun night. Fresh to strong winds will affect the Gulf of Honduras each night beginning tonight through Mon 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 and the Yucatan Peninsula. A diffluent pattern aloft between this trough and an anticyclonic circulation over the south-central Caribbean is helping to support scattered showers and tstms across the Caribbean waters from 15N-20N between the tropical wave along 73W and 85W. Lightning density indicates frequent lightning with some of the observed convection. As of 1500 UTC, a trough, surface reflection of the upper-level low is analyzed over the NW Caribbean, and extends from 20N85W to the Gulf of Honduras. Abundant tropical moisture will persist across the NW caribbean and the Yucatan Peninsula on Fri. ATLANTIC OCEAN... An upper-level trough extends from a cyclonic circulation centered near 27N65W to eastern Cuba. Scattered showers and tstms are noted on the SE semicircle of the low affecting mainly the waters from 24N-29N between 60W and 70W. A diffluent pattern aloft between the aforementioned upper-level trough and an anticyclonic circulation located E of the Lesser Antilles is helping to induce this convective activity. Lightning data also indicate frequent lightning with some of the perceived convection. High pressure of 1029 mb centered near 33N34W extends a ridge across the forecast area. Fresh trades are noted along the southern periphery of the ridge, but mainly between 40W-70W. This high pressure will slowly shift westward through Sat night, then remain nearly stationary near 30N55W through Tue. The tightening pressure gradient that results over the central Atlantic will support fresh to strong trade winds and seas of 8-10 ft E of the Lesser Antilles to about 45W by early Sat morning. These marine conditions will persist on Sun. The Saharan Air Layer (SAL) from CIMSS and visible satellite imagery confirme the presence of African dust between the west coast of Africa and the Lesser Antilles, more concentrated E of 50W. For additional information please visit http://www.hurricanes.gov/marine $$ GR