000 AXNT20 KNHC 192336 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 736 PM EDT Sat Aug 19 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 1800 UTC surface analysis and satellite imagery through 2315 UTC. ...SPECIAL FEATURES... Harvey is downgraded to a tropical depression at 19/2100 UTC. At this time, the center of Harvey is near 14.1N 70.0W or about 120 nm NNW of Curacao, and about 770 nm E of Cabo Gracias a Dios on the Nicaragua/Honduras border moving W or 275 degrees at 19 kt. Estimated minimum central pressure is 1007 mb. Maximum sustained wind speed is 30 kt with gusts to 40 kt. Some slow strengthening is possible during the next couple of days, and Harvey could regain tropical storm status Sunday or Sunday night. Satellite imagery indicates that the strong convection associated with Harvey remains west of the center, and covers the area from 12N- 16N between 69-72W. Interests in the central and western Caribbean Sea, northern Nicaragua, northern Honduras, Belize, and the Yucatan Peninsula of Mexico should monitor the progress of Harvey. See the latest NHC Forecast/Advisory under AWIPS/WMO headers MIATCMAT4/WTNT24 KNHC for more details. ...TROPICAL WAVES... A tropical wave extends from 21N43W to 10N44 moving W at 15-20 kt. Satellite imagery indicates a large area of cloudiness but convection is limited in association with this wave. Saharan dust surrounds the wave. This system coincides with a well defined 700 mb trough, and a high amplitud northward bulge of moisture is noted on the TPW product. The wave is embedded in a dry air mass, and upper-level winds are expected to become too strong to support development in a couple of days. Therefore, tropical cyclone formation is not likely while this system moves northwestward at about 13 kt. A tropical wave is over the western Caribbean and extends from western Cuba, along 81W/82W to near 10N82W moving W at 10-15 kt. The wave shows up very well on the TPW animation and 700 mb streamline analysis. Energy from the wave has fractured to the N-NE and is analyzed as a surface trough between the NW Bahamas and the Florida peninsula. The trough extends from 23N79W to 28N77W. Currently, the wave is helping to induce showers and thunderstorms over central Cuba, and near the Cayman Islands. Showers and thunderstorms are also noted ahead of the wave axis over eastern Honduras and eastern Nicaragua. ...ITCZ/MONSOON TROUGH... The monsoon trough extends from the African coast near 12N16W to 09N20W to 10N29W. The Intertropical Convergence Zone axis extends from 10N47W to 09N61W. Scattered moderate convection is from 08N- 10N between 27W-31W, and from 09N-12N between 51W-55W. ...DISCUSSION... GULF OF MEXICO... A large and well defined upper-level low centered over the SE Gulf near 24N85W continues to generate scattered showers and thunderstorms, particularly between 85W-90W, including the northern Yucatan peninsula. A surface trough, reflection of this upper-level low is analyzed on the 2100 UTC surface map from 30N83W to 24N86W. A scatterometer pass showed very well the wind shift associated with this trough. The western half of the Gulf is under the influence of a ridge, anchored by a 1017 mb high pressure centered near 28N94W. Isolated showers and light to gentle anticyclonic winds prevail W of 90W. The upper-low will drift westward reaching the central Gulf on Monday. This system will continue to enhance the development of showers and tstms across the Gulf waters on Sunday. CARIBBEAN SEA... The primary area of concern across the Caribbean Sea is Tropical Cyclone Harvey, forecast to move across the central and western Caribbean through Monday. Please, see Special Features section for more details. A tropical wave is along 81W/82W. Please, see the Tropical Waves section for details. Moisture associated with this tropical wave will continue to affect the northern central America and NW Caribbean, including also western Cuba, increasing the likelihood of showers and thunderstorms on Sunday. ...HISPANIOLA... Daytime heating, local sea breezes, and mountain upslope lifting will combine with available moisture to produce scattered showers and thunderstorms across the island mainly during the afternoon and evening hours through the weekend. ATLANTIC OCEAN... As previously mentioned, the northern part of the tropical wave currently moving acrosss the western Caribbean is analyzed as a trough between the NW Bahamas and the Florida peninsula. This trough is generating scattered showers and tstms, and will continue to move westward across south Florida and the Straits of Florida tonight and Sunday accompanied by active weather. Showers and thunderstorms are forecast to increase across south Florida tonight, and continue on Sunday, with possible locally heavy rain. Another trough is analyzed NE of the Leeward Islands and extends from 24N59W to near Barbuda. This trough continues to produce disorganized showers and thunderstorms mainly from 19N-23N between 58W-63W. Environmental conditions are not expected to be conducive for development of this system during the next couple of days while it moves west-northwestward at 15 to 20 kt. Conditions could become slightly more conducive for development once the system is near the northern Bahamas or Florida around the middle of next week. An area of fresh to strong winds is noted per scatterometer data on the northern side of this trough from 19N- 24N between 57W-63W. The remainder of the Atlantic is under the influence of a ridge, with a center of 1023 mb located near 32N40W. Fresh to strong Northerly winds are aslo noted between the coast of Africa and the Madeira/Canary Islands. These winds are the result of the pression gradient between the Atlantic ridge and lower pressures over west Africa. For additional information please visit http://www.hurricanes.gov/marine $$ GR