350 AXNT20 KNHC 112356 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 756 PM EDT Tue Sep 11 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 1800 UTC surface analysis and satellite imagery through 2315 UTC. ...SPECIAL FEATURES... Hurricane Florence is centered near 27.5N 67.1W at 11/2100 UTC or 310 nm SSW of Bermuda moving WNW at 15 kt. Estimated minimum central pressure is 945 mb. Maximum sustained wind speed is 120 kt with gusts to 145 kt. Latest satellite imagery shows numerous strong convection near the center from 27N-30N between 66W-69W. Scattered moderate to isolated stromg convection is elsewhere from 25N-31N between 64W-70W. A motion toward the west-northwest and northwest is expected through early Thursday. Florence is expected to slow down considerably by late Thursday into Friday. On the forecast track, the center of Florence will move over the southwestern Atlantic Ocean between Bermuda and the Bahamas through Wednesday, and approach the coast of North Carolina or South Carolina in the hurricane warning area on Thursday and Friday. Florence is a category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. Further strengthening is forecast tonight and Wednesday. While some weakening is expected on Thursday, Florence is forecast to be an extremely dangerous major hurricane through landfall. Public Advisories for Florence are issued under WMO header WTNT31 KNHC and under AWIPS header MIATCPAT1. Forecast/Advisories for Florence are issued under WMO header WTNT21 KNHC and under AWIPS header MIATCMAT1. Tropical Storm Isaac is centered near 14.6N 51.3W at 11/2100 UTC or 580 nm E of the Lesser Antilles moving W at 15 kt. Estimated minimum central pressure is 996 mb. Maximum sustained wind speed is 60 kt with gusts to 75 kt. Latest satellite imagery shows numerous strong convection 13N-16N between 49W-51W. Scattered moderate convection is elsewhere from 12N-18N between 48W-52W. Isaac is anticipated to move near or over the central Lesser Antilles on Thursday, move into the eastern Caribbean Sea Thursday night, and move into the central Caribbean Sea by the weekend. Isaac is expected to be near hurricane strength when it moves through the central Lesser Antilles, with some weakening forecast afterward on Friday and Saturday. Public Advisories for Isaac are issued under WMO header WTNT34 KNHC and under AWIPS header MIATCPAT4. Forecast/ Advisories for Isaac are issued under WMO header WTNT24 KNHC and under AWIPS header MIATCMAT4. Hurricane Helene is centered near 17.2N 34.9W at 11/2100 UTC or 630 nm W of the Cabo Verde Islands moving NW at 10 kt. Estimated minimum central pressure is 968 mb. Maximum sustained wind speed is 90 kt with gusts to 110 kt. Latest satellite imagery shows scattered moderate to strong convection from 15N-22N between 32W-37W. Helene is forecast to turn toward the north-northwest on Wednesday. Thereafter, Helene should recurve northeastward with increasing forward speed. Helene should weaken to a tropical storm on Thursday. Public Advisories for Helene are issued under WMO header WTNT33 KNHC and under AWIPS header MIATCPAT3. Forecast/Advisories for Helene are issued under WMO header WTNT23 KNHC and under AWIPS header MIATCMAT3. An area of disturbed weather located over the extreme northwestern Caribbean Sea and the southeastern Gulf of Mexico continues to show some signs of organization. Upper-levels winds are forecast to become more conducive for development, and a tropical depression is likely to form by Thursday night while the disturbance moves across the western Gulf of Mexico. If necessary, an Air Force reconnaissance plane will investigate the system tomorrow. Interests across northeastern Mexico and the coasts of Texas and Louisiana should monitor the Hurricane Florence near 26.7N 65.3W 950 mb at 11 AM EDT moving WNW at 14 kt. Maximum sustained winds 115 kt gusts 140 kt. Florence will move to 27.7N 67.6W this evening, 29.4N 70.6W Wed morning, 31.1N 73.1W Wed evening, and will move to a position north of the area near 32.6N 75.2W Thu morning. progress of this system. Regardless of development, heavy rainfall and gusty winds are expected to continue over western Cuba and portions of the northeastern Yucatan Peninsula through tonight. This area of disturbed weather has a medium chance for tropical cyclone formation over the next couple of days. Please read the latest Tropical Weather Outlook under WMO header ABNT20 KNHC, and under the AWIPS header MIATWOAT for more details on this evolving system. ...TROPICAL WAVES... Tropical waves are not presently over water, however, the next tropical wave expected to move across the discussion area waters in the short-term is presently over the interior of Africa near 12W. Ahead of this wave, scattered moderate to isolated strong convection is observed along the coast of W Africa from 08N-20N between 12W-22W. ...MONSOON TROUGH/ITCZ... The monsoon trough is non-continuous over the interior of Africa. The western segment of the trough extends southwestward from coast of Sierra Leone to 06N18W. The ITCZ is not analyzed at this time. ...DISCUSSION... GULF OF MEXICO... See Special Features above for details on an area of disturbed weather over the southeastern Gulf of Mexico. A narrow upper-level trough extends from the northeastern part of the Gulf of Mexico to the eastern central Gulf of Mexico and to an upper-level low at 23N88W, It continues from the low to inland the eastern Yucatan Peninsula. Associated upper cyclonic flow is present south of 29N Hurricane Florence near 26.7N 65.3W 950 mb at 11 AM EDT moving WNW at 14 kt. Maximum sustained winds 115 kt gusts 140 kt. Florence will move to 27.7N 67.6W this evening, 29.4N 70.6W Wed morning, 31.1N 73.1W Wed evening, and will move to a position north of the area near 32.6N 75.2W Thu morning. and east of 93W. Upper-level anticyclonic wind flow covers the Gulf of Mexico west of 93W and the Atlantic Ocean to 70W, and the Caribbean Sea from 15N northward from 70W westward. Aside from the convection associated with the above described area of disturbed weather over the southeastern gulf waters, isolated showers and thunderstorms are noted elsewhere east of 91W. A stationary front stretches from southwestern Louisiana to inland the southern Texas coast. Plenty of deep atmospheric moisture is present over the far western gulf as a rather strong upper trough moves across central Texas. Scattered moderate isolated strong convection is noted north of 22N and west of a line from 30N91W to 25N94W to 22N95W. Scattered showers and isolated thunderstorms are elsewhere west of 91W. A surface trough in the western Caribbean Sea will move across the Yucatan peninsula on Tue, and into the Gulf of Mexico on Wed. The trough is expected to move into the western Gulf on Thu and to the west of the area on Sat. CARIBBEAN SEA... A surface trough extends from the southeastern Gulf of Mexico near 25N84W to just inland the eastern section of the Yucatan Peninsula. An upper-level trough extends from an upper-level low just north of the Yucatan Peninsula south-southwestward to just inland the peninsula. Plenty of available deep tropical moisture along with the presence of these features has resulted in plenty of atmospheric instability, leading to numerous moderate to strong convection north of 18N and west of 81W, including western Cuba and the Yucatan Channel. This activity is likely to be accompanied by strong to near gale force gusty winds and very heavy rainfall as it gradually lifts northward over the eastern and central Gulf of Mexico through Thu. See Special Features section above for more details on this area of disturbed weather. Scattered showers and isolated thunderstorms are elsewhere north of 15N and west of 81W. ATLANTIC OCEAN... Please refer to the Special Features section above for details on Hurricanes Florence and Helene and on Tropical Storm Isaac. An upper-level trough extends from a nearly stationary upper- level low near 31N34W southwestward to 26N40W, where it becomes a cyclonic shear axis to a small upper-level low dropping south at 24N48W and to near 23N55W. Upper-level cyclonic flow covers the area generally to the north of 23N between 26W and 54W. Scattered showers and isolated thunderstorms are within 120 nm in the NE and 90 nm in the SW semicircles of the low near 24N48W, and also north of 30N from 34W to 38W. Isolated showers and thunderstorms are elsewhere west of 40W, except for scattered showers and isolated thunderstorms north of 26N west of 74W enhanced by the combiation of an inverted surface trough that is offshore the coast of Florida from 26N79W to 31N81W, and an upper trough axis that extends into the far northwest corner of the area from 32N79W to northeastern Florida. For additional information please visit http://www.hurricanes.gov/marine $$ Formosa