000 AXNT20 KNHC 231742 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 142 PM EDT FRI SEP 23 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 Karl is centered near 29.1N 65.3W at 23/1800 UTC or about 200 nm S of Bermuda moving NNW or 335 degrees at 10 kt. Estimated minimum central pressure is 990 mb. Maximum sustained wind speed is 50 kt with gusts to 60 kt. Some strengthening is forecast during the next 48 hours, and Karl is expected to become a hurricane on Saturday. Numerous moderate and isolated strong convection is noted within about 150 nm NW semicircle. Similar convection is in a 90 nm wide band to the NE and E of the center. On the forecast track, the center of Karl should pass near or to the east of Bermuda late tonight or early Saturday. See latest NHC Intermediate Public Advisory under AWIPS/WMO headers MIATCPAT2/ WTNT32 KNHC and the full Forecast/Advisory under AWIPS/WMO headers MIATCMAT2/WTNT22 KNHC for more details. Tropical Storm Lisa is centered near 22.2N 36.3W at 23/1500 UTC or about 790 nm WNW of the Cape Verde Islands and about 1065 nm SSW of the Azores moving NW at 6 kt. This motion with a faster forward speed is expected to continue through Saturday night. A turn toward the north-northwest is forecast on Sunday. Estimated minimum central pressure is 1008 mb. Maximum sustained wind speed is 35 kt with gusts to 45 kt. Weakening is forecast during the next 48 hours due to strong wind shear, and Lisa is expected to weaken to a tropical depression tonight and become a remnant low this weekend. Numerous moderate convection is within about 150 nm NE quadrant. See latest NHC Forecast/Advisory under AWIPS/WMO headers MIATCMAT3/WTNT23 KNHC for more details. ...TROPICAL WAVES... A tropical wave is added to the 1200 UTC analysis/surface map along 17W based on surface data and the TPW product that depicts a low amplitude moisture surge in association with this feature. In addition...the wave remains within broad 700 mb troughing located E of 20W. This wave is forecast to move rapidly westward across the tropical Atlantic Ocean at about 20 kt for the next several days. Environmental conditions could be conducive for some gradual development while the system approaches the Lesser Antilles next week. A 5-day TPW loop indicates that another tropical wave is along 50W extending from 11N-19N. This wave previously spawned tropical cyclone Lisa. The wave shows up reasonably well in the TPW product and 700 mb streamline analysis. A tropical wave is currently moving across the Bay of Campeche where is generating some shower and thunderstorm activity. The wave axis is along 93W south of 20N moving W at 15 kt. The most recent scatterometer pass showed the wind shift associated with the wave. ...ITCZ/MONSOON TROUGH... The Monsoon Trough extends from the African coast near 10N13 to 08N20W to 06N30W. Isolated moderate convection is from 05N-07N between 20W-30W. ...DISCUSSION... GULF OF MEXICO... A 1018 mb high pressure located over north-central Gulf will dominate the region over the weekend producing mainly gentle to moderate E-SE winds. As previously mentioned, a tropical wave is moving across the Bay of Campeche, likely enhancing the thermal trough that usually develops each afternoon and evening over the Yucatan Peninsula and moves westward over the Bay of Campeche during the overnight hours. A narrow band of showers with embedded thunderstorms is noted along the Florida Keys and the SE Gulf likely associated with a surface trough analyzed just E of Florida and an upper level trough that extends from southern Georgia to the central Gulf near 24N90W. This trough supports a 1012 mb low centered along coastal South Carolina. Early next week...SE winds will increase slightly across the western Gulf ahead of a cold front forecast to emerge off the Texas and Louisiana coasts sometime between Monday night and Tuesday. CARIBBEAN SEA... Weak pressure gradient is noted across the Caribbean Sea due to the presence of Tropical Storm Karl located NE of the area. As a result, mainly gentle to moderate trades are blowing across the basin. A ridge extending from the central Atlantic reaches The Lesser Antilles. Scattered showers and thunderstorms are over the NW Caribbean, with a cluster of moderate to strong convection just off the coast of Nicaragua. A diffluent pattern aloft is helping to induce this convective activity. As Karls continues to move away from the forecast area, the subtropical ridge will build back increasing slightly the trade wind flow across the area. Computer model suggests fresh to locally strong trade winds over the south-central Caribbean this upcoming weekend but mainly during the overnight and early morning hours. ...HISPANIOLA... Available moisture will combine with the local effects and an upper-level low located over the island to provide an overall favorable environment for scattered showers and thunderstorms this weekend, particularly during the afternoon and early evening hours. ATLANTIC OCEAN... A surface trough is just E of Florida and extends from 31N79W to the Florida Keys. Scattered showers and thunderstorms are along the trough axis that continues over the SE Gulf of Mexico. Aloft... southwesterly winds are transporting abundant mid to upper level moisture from the Gulf of Mexico across South Florida into the western Atlantic, keeping the atmosphere very moist and unstable over the area. Farther east...Tropical Storm Karl and Tropical Storm Lisa continue to affect the forecast region. Please, see the Special Features section for details. Otherwise...the remainder of the central and eastern Atlantic is under the influence of a surface ridge anchored by a 1026 mb high centered near 32N45W and a 1027 mb high centered between the Azores and the Canary Islands near 32N23W. The pressure gradient between the ridge and a weak 1012 mb low pressure located near 17N17W is resulting in area fresh to strong NE winds north of 19N to the Canary Islands and E of 20W. an Ascat pass confirmed the presence of these winds. For additional information please visit http://www.hurricanes.gov/marine $$ GR