000 AXNT20 KNHC 191801 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 201 PM EDT FRI AUG 19 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 1715OPC UTC. ...SPECIAL FEATURES... Tropical Storm Fiona is centered near 17.8N 43.5W at 19/1500 UTC or about 1125 nm/2080 km west of the Cabo Verde Islands, moving WNW or 295 degrees at 9 kt. Estimated minimum central pressure is 1006 mb. Maximum sustained wind speed remains 40 kt with gusts to 50 kt. Fiona continues to produce bursts of convection, mainly near and north of the center, with the low-level center partly exposed south of the convective area. Some weakening is forecast during the next 48 hours, and Fiona is expected to weaken to a depression over the weekend due to a combination of a dry air mass and increasing vertical wind shear. See latest NHC Forecast/Advisory under AWIPS/WMO headers MIATCMAT1/WTNT21 KNHC for more details. ...TROPICAL WAVES... A tropical wave extends from 18N31W to a 1009 mb low pressure located 10.5N31W. This system is producing a disorganized area of cloudiness and shower activity. In fact...latest satellite imagery indicates that convection has diminished some in association with this low over the past few hours. Environmental conditions are expected to be conducive for gradual development, and a tropical depression could form early next week while the system moves westward at about 10-15 kt across the tropical Atlantic Ocean. Currently, the Tropical Weather Outlook gives this low pressure a low change of tropical development through 48 hours and a medium chance of tropical formation through 5 days. A tropical wave is over the eastern Caribbean and extends from 18N61W to 10N62W. Some shower activity is noted over the Lesser Antilles. Moisture is limited in association with this wave forecast to move across the eastern Caribbean tonight through Saturday night. A second tropical wave is moving westward across the Caribbean Sea and extends from the Windward Passage to the coast of Colombia near 10N74W. This system is better defined on the TPW product and 700 mb streamlines. The wave is enhancing the trade wind flow across the central Caribbean where scatterometer data indicate fresh to strong easterly winds just behind the wave axis. Shallow moisture, embedded in the trade wind flow, is noted moving westward across this area. The wave will move across central and western Caribbean through Saturday night. ...ITCZ/MONSOON TROUGH... The Monsoon Trough extends from the African coast near 14N17W to a 1009 mb low pressure near 10.5N31W to 09N35W to 11N43W. The Intertropical Convergence Zone axis continues from 11N43W to to 10N50W to the coast of Venezuela near 09N61W. Isolated to scattered moderate convection is noted from 8N-10N between 14N- 17N, from 8N-10N between 35W-38W and within about 90 nm north of axis between 52W-57W. ...DISCUSSION... GULF OF MEXICO... Weak high pressure of 1020 mb located over the NE Gulf dominates the area while a thermal trough is over the Bay of Campeche extending from 22N92W to 18N94W. Isolated showers are noted just ahead of the trough south of 20N. This thermal through will support fresh NE-E winds along the NW coast of the Yucatan peninsula and across the Bay of Campeche at night. The weak ridge across the Gulf region will produce mainly gentle to moderate winds during the upcoming weekend. A few showers are also noted over the NW Gulf under a southerly wind flow. Aloft, an upper level trough extends from south Florida to an upper-level low spinning near 23N87W to the Bay of Campeche. Subsidence and implied dry air mass in noted on water vapor imagery N of the trough axis while SW to W winds ahead of the trough are transporting abundant mid-upper level moisture from SE Mexico across western Cuba into the NW Bahamas. Little change is expected in the weather pattern across the Gulf region over the weekend under the influence of a ridge. CARIBBEAN SEA... Two tropical waves are moving across the Caribbean Sea. Please see the tropical waves section for details. Tropical cyclone Fiona now located well E of the area should pass NE of the basin over the next few days and it is unlikely to produce significant winds or seas in the Caribbean Sea. The most recent scatterometer data captured an area of fresh to strong winds across the central Caribbean, including the Gulf of Venezuela. Trades are reaching near gale force near the coast of Colombia at night. This weather pattern is forecast to persist during the upcoming weekend. Satellite imagery shows low-topped trade wind showers moving westward across the region. Scattered showers and thunderstorms are noted over the SW Caribbean, likely associated with the E Pacific monsoon trough. In the upper-levels, a ridge extends across the NE Caribbean, including Puerto Rico and Hispaniola. The ridge will produce a generally stable weather pattern across the region limiting convection. However, isolated to scattered showers and isolated thunderstorms may occur due to local effects in the afternoon. ...HISPANIOLA... As previously mentioned, an upper-level ridge across the island will produce a mainly stable weather pattern across Hispaniola this weekend. As a result, expect only isolated to scattered showers and isolated thunderstorms in the afternoon due to daytime heating, local sea breezes and mountain upslope lifting. ATLANTIC OCEAN... The main feature in the basin is T.S. Fiona discussed in the special features section followed by a low pressure along the tropical wave located near 31W. Some of the global models develop this low pressure into a tropical cyclone by early next week. Weak ridge dominates the remainder of the area with a 1021 mb high near 29N29W forecast to move just N of the forecast region in about 24 hours. Scatterometer passes indicate mainly light to gentle winds across the Atlantic under the influence of the ridge and well outside of the tropical systems. An upper-level trough extending from 31N71W to south Florida is helping to induce some shower and thunderstorm activity across the NW Bahamas and the Atlantic waters W of 60W. For additional information please visit http://www.hurricanes.gov/marine $$ GR