000 AXNT20 KNHC 211751 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 151 PM EDT SUN AUG 21 2016 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. ...SPECIAL FEATURES... Tropical Storm Fiona is centered near 22.9N 53.3W at 21/1500 UTC or about 590 nm/1095 km NE of the Leeward Islands, moving WNW or 295 degrees at 14 kt. Estimated minimum central pressure is 1007 mb. Maximum sustained wind speed is now 35 kt with gusts to 45 kt. Fiona has weakened a little more this morning and it is forecast to become a tropical depression later today or tonight. Strong westerly shear continues to affect Fiona. As a result, a cluster of moderate to isolated strong convection is noted within about 90 nm NW semicircle of the center with scattered moderate convection elsewhere around the small circulation. Please see latest NHC Forecast/Advisory under the AWIPS/WMO headers MIATCMAT1/WTNT21 KNHC for more details. Tropical wave is just off the west coast of Africa extending from 17N19W to a 1009 mb low pressure 12N19W to 08N19W. Scattered moderate isolated strong convection is noted mainly N of the low center and ahead of the wave axis from 12N-15N between 19W-21W. Environmental conditions are conducive for development, and a tropical depression is likely to form during the next day or two while the system moves westward and then northwestward over the eastern tropical Atlantic Ocean. The low pressure is forecast by the computer models to be near 12N26W in about 24 hours. The Tropical Weather Outlook gives this system a high chance of tropical cyclone development through 48 hours. ...TROPICAL WAVES... Tropical wave is in the central Atlantic extending from 20N42W to 10N43W. A 1010 mb low pressure is along the wave axis near 14N43W. Convection is limited in association with this wave due to the presence of Saharan dust based in the current SAL analysis. Visible satellite imagery shows a large swirl of mainly low clouds related to the low pressure. The proximity of this system to dry air is expected to inhibit significant development during the next few days while the disturbance moves westward to west- northwestward at 15 to 20 mph. Environmental conditions could become more conducive for development late this week when the system is expected to be near Hispaniola and the southeastern Bahamas. Moisture associated with this system is expected to reach the Leeward Islands and part of the Windward Islands by Tuesday evening or night. Tropical wave in the central Caribbean extends from Haiti to the coast of Colombia near 11N73W, moving W at 10 kt within the last 24 hours. No deep convection is associated with the wave. This feature is enhancing the trade wind flow across the central Caribbean. The wave will continue to move westward across the W Caribbean through Tuesday night. ...ITCZ/MONSOON TROUGH... The Monsoon Trough extends across Africa into the east Tropical Atlantic near 14N17W to 09N25W to 12N39W. The ITCZ begins near 10N46W to 08N53W to the coast of Venezuela near 10N62W. Scattered moderate isolated strong convection is from 07N-10N between 19W- 28W. ...DISCUSSION... GULF OF MEXICO... A 1018 mb high pressure located over the NE Gulf dominates the area while a thermal trough is over the Bay of Campeche along 94W/95W. The high pressure will shift NW toward the Mississippi delta through Tuesday. The trough will support fresh to strong NE-E winds just off the NW coast of the Yucatan peninsula and across the SW Gulf tonight and then again Monday night. Doppler radar shows scattered showers and isolated thunderstorms moving northward across the NW Gulf into the coast of Texas in a moderate southerly wind flow. Light to gentle winds are noted over the NE gulf due to the presence of the high center. Aloft, an elongated upper-level low is over the SW Gulf and SE Mexico. Southerly winds on the east side of the low are advecting abundant mid-upper level moisture over SE Mexico and northern central America. CARIBBEAN SEA... A tropical wave is moving westward across the Caribbean Sea. Please see the tropical waves section for details. The most recent scatterometer data provided observations of fresh to strong winds are across the central Caribbean. Shallow moisture, embedded in the trade wind flow is moving westward across the basin producing isolated to scattered passing showers. An area of cloudiness, with embedded showers, is noted across the Atlantic waters of the UK/US Virgin Islands and Puerto Rico moving westward. This surge of moisture is expected to cross Puerto Rico tonight reaching Dominican Republic by Monday morning increasing the likelihood of showers. Aloft, an upper-low is spinning over western Cuba and is currently generating some cloudiness with isolated showers. An anticyclonic circulation is centered over Nicaragua helping to induce some convective activity over eastern Nicaragua. An inverted trough lies over the central Caribbean with axis along 75W and extends southward into Colombia. The remainder of the Caribbean is under the influence of a ridge anchored by an upper-level anticyclone located E of the area near 18N48W. ...HISPANIOLA... Moisture is forecast to increase across the island Monday and Tuesday as a surge of moisture, currently affecting Puerto Rico, reach Hispaniola. This combined with the local effects will likely support scattered showers and isolated thunderstorms. ATLANTIC OCEAN... T.S. Fiona is weakening. Please see the Special Features section above for more details. Attention remains focused on the tropical wave and associated low pressure located over the central Atlantic. This system is forecast to move through the eastern Caribbean Sea and portions of the Greater Antilles early this week and then emerge north of Hispaniola near the southeastern Bahamas later this week. The chance of tropical cyclone formation is assessed to be low in the short term, however, conditions could become more conducive for some slow development longer term. A ridge covers the remainder of the forecast area with a 1022 mb high pressure located NE of Fiona near 29N36W. A 1018 mb high pressure is near 24N67W forecast to move NW to a position near 25N72W in about 24 hours. Scattered moderate convection is just N of area from 30N-32N between 70W-78W. A diffluent pattern aloft supports this convective activity. For additional information please visit http://www.hurricanes.gov/marine $$ GR