559 AXNT20 KNHC 120532 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 132 AM EDT Wed Sep 12 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 0000 UTC surface analysis and satellite imagery through 0515 UTC. ...SPECIAL FEATURES... Hurricane Florence is centered near 28.4N 68.7W at 12/0300 UTC or 310 nm SW of Bermuda moving WNW at 15 kt. Estimated minimum central pressure is 946 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 65W-69W. Scattered moderate to isolated stromg convection is elsewhere from 25N-31N between 64W-71W. 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 through 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 14.5N 52.3W at 12/0300 UTC or 500 nm E of Martinique moving W at 14 kt. Estimated minimum central pressure is 999 mb. Maximum sustained wind speed is 55 kt with gusts to 65 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 Friday or Saturday. Gradual weakening is forecast during the next few days. 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 centered near 18.0N 35.4W at 12/0300 UTC or 660 nm WNW of the Cabo Verde Islands moving NW at 9 kt. Estimated minimum central pressure is 973 mb. Maximum sustained wind speed is 85 kt with gusts to 105 kt. Latest satellite imagery shows scattered moderate to strong convection from 15N-22N between 32W- 37W. Helene is forecast to turn toward the north Thursday. Helene is forecast to accelerate and turn toward the northeast by the end of the week. Gradual weakening is likely over the next couple of days, and Helene is expected to become a tropical storm by 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 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. 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 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... A Tropical wave is along the coast of W Africa along 17W south of 18N, moving W at 15Kt. A distinct 700 mb trough is noted. Widely scattered moderate convection is observed along the coast of W Africa from 08N-20N between 12W-22W. ...MONSOON TROUGH/ITCZ... The monsoon trough extends from W Africa near 11N15W to 06N17W to 04N22W. Isolated moderate convection is from 03N-06N between 16W-22W. ...DISCUSSION... GULF OF MEXICO... See Special Features above for details on an area of disturbed weather over the southeastern Gulf of Mexico. A surface trough extends from the SE Gulf of Mexico near 27N87W to the Yucatan Peninsula near 18N90W. A 1010 mb low is embedded on the trough near 23N88W. Isolated moderate convection is within 120 nm of the trough. Elsewhere, isolated moderate convection is over the Florida Peninsula. In the upper levels, an upper level low is also centered near 23N89W drifting W. Upper level diffluence is noted inland over S Mexico producing scattered moderate to isolated strong convection S of 22N. CARIBBEAN SEA... Widely scattered moderate convection is over the NW Caribbean and Central America W of 85W. Elsewhere, scattered moderate convection is over S Haiti. The eastern extent of the E Pacific monsoon trough is over Costa Rica and Panama along 09N. Scattered moderate convection is within 120 nm S of the monsoon trough. A 1008 mb low is centered over N Colombia near 09N74W. In the upper levels, an upper level low is centered over N Colombia near 12N73W. An upper level high is centered just E of the Leeward Islands near 16N59W. Expect Isaac to enter the Caribbean Sea on Thursday. ATLANTIC OCEAN... Please refer to the Special Features section above for details on Hurricanes Florence and Helene and on Tropical Storm Isaac. Scattered showers are over the central Atlantic N of 29N between 40W-50W due to a cold front N of the area. In the upper levels, a small upper level low is centered N of the Bahamas near 29N78W. Scattered showers are over the N Bahamas. For additional information please visit http://www.hurricanes.gov/marine $$ Formosa