000 AXNT20 KNHC 111741 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 141 PM EDT Fri Aug 11 2017 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... A tropical wave is added to the 1200 UTC analysis/surface map along 17W/18W based on visible satellite imagery and the Hovemoller Diagram that shows the westward propagation of the wave since August 9. In addition, the wave shows up very well on the TPW animation and 700 mb streamline analysis. Scattered moderate convection is where the wave meets the monsoon trough from 10N-12N between 16W-19W. Another tropical is midway between the coast of Africa and the Lesser Antilles and extends from 19N38W to 10N39W moving W at 10-15 kt. The wave coincides with a well defined 700 mb trough, and a high amplitud northward bulge of moisture is noted on the TPW product, mainly to the east of the wave axis. African dust surrounds the wave, which is limited the convection to only isolated showers near the wave axis. A tropical wave extends from 19N70W to 10N71W moving W at 10-15 kt. The wave coincides with a 700 mb trough, and is well depicted in the moisture product. The wave is currently helping to induce some shower activity over Dominican Republic. This wave will move across the rest of Hispaniola and the central Caribbean today, then slow somewhat as it continues through the western Caribbean through Sunday night. ...ITCZ/MONSOON TROUGH... The monsoon trough extends from the African coast near 12N16W to 10N25W to 11N34W to 09N38W. The Intertropical Convergence Zone axis continues from 09N38W to 07N50W to 06N57W. Aside from convection associated with the tropical waves, scattered moderate convection is from 07N-12N between 19W-30W. Isolated moderate convection is from 07N-10N between 30W-38W. ...DISCUSSION... GULF OF MEXICO... A surface ridge, with axis across the north waters, dominates the Gulf region producing mainly light to gentle winds across the area N of 25N, and gentle to moderate winds S of 25N, with the exception of moderate to fresh winds near and to the NW of the Yucatan Peninsula due to the presence of a thermal trough. A 1020 mb high pressure is along the ridge near 29N87W, and will be nearly stationary across the NE and north-central Gulf waters through the weekend. A surface trough is over Florida and the SE Gulf generating some shower and tstm activity. The trough will drift westward across Florida through Saturday as the Atlantic ridge begins to build westward. Abundant moisture will persist across the eastern Gulf through at least late Saturday. An upper- level anticyclonic circulation centered over the Rio Grande River valley near 30N100W is providing a N-NE upper level flow across much of the basin. CARIBBEAN SEA... A tropical wave is along 70W/71W. Please, see Tropical Waves section for details. The most recent scatterometer data indicate fresh to locally strong winds across the south-central Caribbean, in the Gulf of Honduras, and also across the Windward Passage. The pressure gradient over the area will continue to support fresh to locally strong nocturnal trades over the far south-central portions of the Caribbean south of about 13N to include portions of the coasts of Colombia and Venezuela and Gulf of Venezuela through late Sunday night. The pressure gradient is forecast to tighten early next week as the Atlantic ridge builds westward. This will allow for these winds to expand northward across the central Caribbean to near 17N by Tuesday. Expect building seas to 8-10 ft with the strongest winds. Clusters of moderate to isolated strong convection are noted over the SW Caribbean, just N of Costa Rica and Panama. A diffluent pattern aloft, associated with an upper-level anticyclonic circulation situated near 13N77W supports this convective activity. Shallow moisture embedded in the trade wind flow is noted elsewhere. ...HISPANIOLA... A tropical wave moving across Hispaniola today will combined with the local effects to produce scattered showers and thunderstorms mainly this afternoon and evening. The tropical wave will move away from the island on Saturday, but an upper-level trough extending across Hispaniola will continue to favor the development of scattered showers and tstms mainly during the afternoon and evening hours. Moisture is forecast to diminish across the island on Sunday. ATLANTIC OCEAN... A trough is N of Puerto Rico and extends from 24N63W to 19N66W. A 1013 mb low pressure is along the trough axis near 22N64W. Scattered moderate convection is noted around the low center, and in a band from 19N-25N between 60W and 63W. The convective activity associated with this system has become a little better organized since yesterday, but there are no indications of a closed circulation. Upper-level winds are forecast to become more favorable for development by the weekend, but dry air aloft could limit additional development of the thunderstorm activity. This makes the overall environment only marginally conducive for tropical cyclone formation. The disturbance is expected to move northwestward today, then northward over the weekend across the western Atlantic Ocean. The latest Tropical Weather Outlook gives this low pressure a medium change of tropical cyclone formation through 48 hours. A recent scatterometer pass provides observations of fresh to strong E-SE winds within about 150 nm NE semicircle of low center. Another weak low is over NE Florida near 29.5N81W. A trough extends from the low center across central Florida to the SE Gulf of Mexico near 25N84W. Mosaic Doppler Radar from the SE U.S. indicates scattered showers and isolated thunderstorms in association with this feature over Florida and coastal waters, including also the Straits of Florida. This system has become less organized and development is not anticipated, but it could still produce locally heavy rains to portions of the Florida peninsula as it moves northward during the next day or two. A third low pressure of 1016 mb is near 29.5N42.5W with a trough extending SW to near 24N48W. Isolated showers and tstms are near the low center. The remainder of the Atlantic Ocean is under the influence of a ridge anchored by a 1030 mb high pressure located NE of the Azores. The ridge is forecast to build westward across the forecast waters early next week, with the high pressure center located SW of the Azores. For additional information please visit http://www.hurricanes.gov/marine $$ GR