271 AXNT20 KNHC 071157 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 757 AM EDT Fri Sep 7 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 0600 UTC surface analysis and satellite imagery through 1145 UTC. ...SPECIAL FEATURES... Tropical Storm Florence is centered near 25.1N 50.7W at 07/0900 UTC or 800 nm ENE of the Northern Leeward Islands, moving W at 6 kt. Estimated minimum central pressure is 996 mb. Maximum sustained wind speed is 55 kt with gusts to 65 kt. Scattered moderate convection is noted from 24N-27N between 46W-52W. The latest NHC forecast calls for Florence to move northwestward through tonight before it turns toward to the west on Fri. It is forecast to weaken slightly today, then re-strengthen beginning this evening, reaching minimal hurricane intensity early on Sat and continue to gradually intensify through the rest of the upcoming weekend. See the latest NHC forecast/advisory under AWIPS/WMO headers Miatcpat5/WTNT31 KNHC for more details. A broad and elongated area of low pressure is centered several hundred miles west of the Cabo Verde Islands is denoted by a tropical wave with its axis along 34W and extending from 04N to 20N. A 1008 mb low is on the wave axis near 14N35W. This system is moving westward at about 10 to 15 kt. The associated shower and thunderstorm activity has increased some during the last couple of hours. Latest satellite imagery shows scattered moderate to strong convection within 150 nm of the low mostly in the W quadrant. Environmental conditions appear conducive for development, and a tropical depression is expected to form within the next day or two while the system moves slowly westward across the tropical Atlantic. The chance of this system becoming a tropical cyclone during the next 48 hours remains in the high range. Please read the latest NHC Tropical Weather Outlook under AWIPS/WMO headers MIATWOAT/ABNT20 KNHC for more information. A tropical wave just off the coast of western Africa has its axis near 17W from 04N to 20N, with a 1006 mb low on the axis near 13N17W. This system is moving westward at 10 to 15 kt. Latest satellite long term animation indicates that this system is exhibiting signs of organization. Very large clusters of numerous strong convection have significantly increased in advance of this system as observed from the coastal sections of Senegal to Sierra Leone, and westward from these locations to 19W. This activity also spreads eastward to within 90 to 120 nm inland the coast of Africa. Environmental conditions appear conducive for development, and a tropical depression or tropical storm is likely to form later today or over the upcoming weekend while the wave and low moves westward or west-northwestward over the far eastern tropical Atlantic Ocean. The chance of this system becoming a tropical cyclone during the next 48 hours is now in the high range. Interests in the Cabo Verde Islands should monitor the progress of this system, and advisories on a potential tropical cyclone or tropical depression could be issued later today. Please read the latest NHC Tropical Weather Outlook under AWIPS/WMO headers MIATWOAT/ABNT20 KNHC for more information. ...TROPICAL WAVES... A tropical wave has its axis along 85W south of 21N, moving westward at 10 to 15 kt. Scattered showers are noted within 90 nm on either side of the wave's axis. A northern portion of a tropical wave extends across southern Mexico along 98W and south of 21N, moving westward near 15 kt. Scattered showers are observed within 60 nm of the wave's axis. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from well inland Africa to the 1006 mb low that is associated with the tropical wave along 17W, and continues to 13N23W. The trough resumes from the 1008 mb low discussed above near 14N35W to 08N42W. The ITCZ begins from this point to 08N56W. Aside from the convection related to the Special Features' lows, scattered moderate convection prevails along the ITCZ. ...DISCUSSION... GULF OF MEXICO... Upper-level cyclonic flow is located over eastern Louisiana and Mississippi while upper-level anticyclonic flow remains over the west-central Gulf of Mexico and strong northeast upper-level winds are over eastern Gulf of Mexico along the western periphery of the large upper low that is over the northwestern Bahamas. A moist and unstable atmosphere along with plenty available instability is allowing for scattered showers and isolated thunderstorms to be over much of the NW Gulf and far western gulf waters. Scattered moderate convection that moved offshore the west coast of Florida last night is seen over the eastern gulf waters from 25N to 30N between 83W and 85W, and over the far southeastern gulf waters just west of the lower Florida Keys to near 84W and from 23N to 25N. Isolated showers and thunderstorms are elsewhere across the basin. Expect for shower and thunderstorm activity to remain over these same gulf waters through at least tonight. Otherwise, weak ridging from the Carolinas to the Texas coast will shift northward through Sat, supporting gentle to moderate easterly winds and modest seas into early next week. The exception will be fresh winds pulsing off west of the Yucatan peninsula, mainly during the late evenings through the next few days. CARIBBEAN SEA... Please see Tropical Waves section above for details regarding a tropical wave along 85W. An upper-level trough axis stretches from central Cuba to 18N83W and to over eastern Honduras. Associated cyclonic flow covers the western Caribbean Sea west of a line from Hispaniola to Panama. Upper-level anticyclonic flow covers the eastern Caribbean as the culprit anticyclone remains anchored near 17N61W. Aside from convection related to the tropical wave, isolated showers and thunderstorms are elsewhere west of 71W. A relatively weak surface ridge in the western Atlantic Ocean will maintain moderate to fresh trade winds in most of the region into Sun. Building high pressure over the eastern Gulf of Mexico will allow fresh to strong E to SE winds and building seas over portions of the NW Caribbean late Sun and Mon. ATLANTIC OCEAN... Please read the Special Features section above for details about Florence and the two waves/lows in the east Atlantic with a chance of tropical development. A large upper-level low centered over the northwestern Bahamas extends a trough southwestward across central Cuba. The low continues progressing in a westward motion. Its associated upper- level cyclonic flow covers the Atlantic west of 66W, and northward to about 35N. A westward moving surface inverted trough is analyzed from 31N76W to the NW Bahamas and to just north of the coast of Cuba near 24N79W. Another surface trough is analyzed from near 31N66W to 29N67W. Available deep atmospheric moisture for these features to work on has resulted in ample instability bringing scattered showers and thunderstorms over the waters north of 25N between 67W and 78W. Isolated showers and thunderstorms are elsewhere west of 65W, and also north of 28N between 50W and 65W. A weak pressure pattern will maintain gentle to moderate easterly winds across the western Atlantic area into early next week. Tropical Storm Florence is forecast by the latest NHC advisory to move across the northeastern NHC/TAFB offshore waters zones Mon through Tue of next week. Easterly swell, in advance of Florence, are forecast to propagate through the open waters east of the Bahamas beginning this upcoming weekend. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre/ERA