000 AXNT20 KNHC 172349 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 749 PM EDT SAT SEP 17 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 1800 UTC surface analysis and satellite imagery through 2330 UTC. ...SPECIAL FEATURES... Tropical Depression Julia is centered near 30.5N 76.3W at 17/2100 UTC or about 235 nm southeast of Charleston, South Carolina. Julia is slowly drifting toward the northwest. Estimated minimum central pressure is 1010 mb. Maximum sustained wind speed is 25 kt with gusts to 35 kt. Scattered moderate convection exists within 180 nm of the center in the eastern semicircle. Please see the latest NHC Forecast/Advisory under the AWIPS/WMO headers MIATCMAT1/WTNT21KNHC for more details. Tropical Storm Karl is centered near 18.1N 40.4W at 17/1500 UTC or about 1225 nm east of the Leeward Islands moving west at 11 kt. Estimated minimum central pressure is 1005 mb. Maximum sustained wind speed is 40 kt with gusts to 50 kt. Scattered moderate and isolated strong convection exists within 240 nm of the center in northeastern semicircle. Please see the latest Forecast/Advisory under the AWIPS/WMO headers MIATCMAT2/WTNT22 KNHC for more details. A surface low is located at 13N20W a couple hundred nm southeast of the Cabo Verde Islands. The low is associated with a tropical wave extending near the 20W longitude from roughly 09N to 17N. Isolated moderate to strong convection is occurring from 09N-16N from 24W eastward to the West Africa coast. Environmental conditions appear conducive for development, and a tropical depression could form by early next week while this system moves westward to west-northwestward across the eastern tropical Atlantic. This system is likely to bring heavy rain and gusty winds to portions of the Cabo Verde Islands during the next couple of days. This system has a medium chance of tropical formation within the next 48 hours. ...TROPICAL WAVES... A tropical wave extends across the central Tropical Atlantic with axis near the 58W longitude extending approximately from 11N to 21N. The wave is moving toward the west at about 10 to 15 kt. The wave coincides with a 700 mb inverted trough depicted by model guidance and is identified by the SUNY-ALBANY trough diagnostics. However, no convection or significant surface features are associated to this feature at this time. ...ITCZ/MONSOON TROUGH... The Monsoon Trough extends from the wave/low described above centered near 13N20W to 14N34W. Aside from the convection related to the tropical wave, scattered moderate convection is observed within 300 nm south of the boundary between 22W-31W. ...DISCUSSION... GULF OF MEXICO... A mid-level trough extends near the Texas coastline from 27N97W to 30N95W. Associated with this trough is a weak 1014 mb surface low near 28N95W. As observed from satellite and radar, scattered moderate convection exists north of 26N between 90W and 95W. The remainder of the Gulf has no significant deep convection. To the southwest, a thermal surface trough extends across the Bay of Campeche from 23N93W to 19N95W. Winds are generally weak across the Gulf veering from 5-10 kt east to southeast winds in the eastern Gulf to 10-15 kt south to southwest winds in the western Gulf. A similar weather pattern will prevail through the next 48 hours. CARIBBEAN SEA... A vigorous upper-level low is centered over the northeastern Caribbean near 17N63W and it is associated with the surface trough extending from 20N62W to 13N64W. Scattered moderate convection is occurring on the east side of the upper low/surface trough from 12N to 16N between 59W and 63W. Enhanced diurnal convection has been occurring over the Greater Antilles and and Central America during the late afternoon hours. Elsewhere no significant deep convection is occurring over the Caribbean. The easterly tradewinds are generally 10-20 kt, except 20 to 25 kt just north of Colombia and in the Gulf of Venezuela. The upper-low and trough should push westward and weaken during the next couple of days. They will also be interacting with a tropical wave that will be entering the Caribbean on Sunday, continuing the likelihood of scattered moderate and isolated strong convection in the Lesser Antilles, Puerto Rico, and Hispaniola for the next couple of days. ...HISPANIOLA... Only isolated moderate convection occurred over the island this afternoon. However, the interaction of a tropical wave with an upper low/surface trough will enhance the chances of scattered moderate and isolated strong convection over Hispaniola during the next couple of days. ATLANTIC OCEAN... Tropical Depression Julia and Tropical Storm Karl are occurring over the Atlantic this evening. Please see the Special Features section above for details. A surface trough extends across the west-central Atlantic from 24N69W to 31N59W. Scattered moderate convection is occurring with 240 nm southeast of the trough axis. The trough should move westward without much change during the next couple of days. The east Atlantic is dominated by a surface ridge anchored by a 1029 mb high centered near the Azores at 37N26W. Except near the tropical cyclones, the trade winds are generally 10-20 kt across the tropical North Atlantic. 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