484 AXNT20 KNHC 151724 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 124 PM EDT Sat Sep 15 2018 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 Florence is centered near 33.6N 79.6W at 15/1500 UTC, or 30 nm W of Myrtle Beach South Carolina, moving W at 2 kt. Estimated minimum central pressure is 995 mb. Maximum sustained wind speed is 40 kt with gusts to 50 kt. Scattered moderate convection prevails north of 31N between 74W-82W. Latest NHC advisory has Florence turning north- westward through the Carolinas and to the Ohio Valley this weekend. Gradual weakening is forecast while Florence moves farther inland during the next couple of days, and it is likely to weaken to a tropical depression in 24 hours. See the latest NHC forecast/advisory under AWIPS/WMO headers MIATCPAT1/WTNT31 KNHC for more details. Tropical Storm Helene is centered near 38.8N 34.0W at 15/1500 UTC, or 130 nm WSW of Flores Island in the western Azores, moving NE at 18 kt. Estimated minimum central pressure is 988 mb. Maximum sustained wind speed is 60 kt with gusts to 75 kt. Scattered moderate convection prevails north of 37N between 30W-37W. Helene is forecast to turn northeast by tonight/early Sun, passing near or over the Azores. See the latest NHC forecast/advisory under AWIPS/WMO headers MIATCPAT3/WTNT33 KNHC for more details. Tropical Storm Joyce is centered near 32.0N 41.0W at 15/1500 UTC or 770 nm WSW of the Azores moving ENE at 12 kt. Estimated minimum central pressure is 1001 mb. Maximum sustained wind speed is 40 kt with gusts to 50 kt. Latest satellite imagery shows scattered moderate convection north of 33N between 38W-42W. Joyce is forecast by the latest NHC advisory to turn northeastward with an increase in forward speed today, with some slight strengthening possible. Gradual weakening is forecast to begin by Sun.See the latest NHC forecast/advisory under AWIPS/WMO headers MIATCPAT5/WTNT35 KNHC for more details. ...TROPICAL WAVES... A far eastern Atlantic tropical wave has its axis along 33W from 08N to 19N, moving westward at 10-15 kt. The wave is surrounded by a rather dry environment, which is inhibiting deep convection from forming along or near it. Only isolated showers are within 75 nm either side of the wave axis, mainly where it crosses the monsoon trough. ...MONSOON TROUGH/ITCZ... The monsoon trough extends from 12N17W to 09N26W. The ITCZ is from 08N38W to 08N59W. Aside from the shower activity associated with the tropical wave along 33W, scattered moderate convection is within 120 nm on either side of the ITCZ. ...DISCUSSION... GULF OF MEXICO... A 1014 mb surface high is centered near 28N87W. T.S. Florence is centered to the northeast of the basin enhancing the pressure gradient across the east Gulf waters. With this, moderate westerly flow prevails north of 28N and east of 86W. To the west, a surface low centered over southern Texas is enhancing scattered to numerous moderate convection north of 21N and west of 96W. An upper-level low is centered over the Yucatan Channel enhancing shower activity south of 25N between 86W-91W. CARIBBEAN SEA... An upper level cyclonic circulation center is located near the Yucatan Channel enhancing scattered showers west of 83W. To the south, the monsoon trough extends along Panama with scattered moderate convection south of 11N between 76W-82W. To the east, the remnants of Isaac are centered near 15N71W. Its pressure is 1006 mb. Scattered moderate convection is observed between 66W-74W affecting the adjacent waters south of Puerto Rico and Hispaniola. Moderate to fresh winds prevail with this low over the central Caribbean. Elsewhere, gentle to moderate trades prevail east and west of the low. Strong nocturnal trades are forecast off the northwest coast of Colombia on Mon and Tue nights. ATLANTIC OCEAN... Please refer to the Special Features section above, for details on Florence, Helene, and Joyce, and the Tropical Waves section for details about the wave along 33W. An upper-level trough extends across the central Atlantic . A 1012 mb surface low has developed near 31N61W. A trough extends from he low to the east along 32N. Scattered moderate convection is developing in the vicinity of these features mainly north of 27N between 57W.64W. A surface ridge will remain about stationary from near 32N68W to southeastern Florida through the weekend. The ridge will shift northward by the middle of the next week. For additional information please visit http://www.hurricanes.gov/marine $$ ERA