351 AXNT20 KNHC 110541 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 141 AM 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 0000 UTC surface analysis and satellite imagery through 0500 UTC. ...SPECIAL FEATURES... The center of Hurricane Florence at 11/0300 UTC is near 25.9N 62.4W. Florence is moving WNW, or 290 degrees, 11 knots. The estimated minimum central pressure is 944 mb. The maximum sustained wind speeds are 120 knots with gusts to 145 knots. Scattered moderate to strong rainshowers are within 30 nm of the center everywhere. People who are in the SE part and the Mid- Atlantic states of the U.S.A. should monitor the progress of FLORENCE. It is possible that storm surge and hurricane watches may be issued for parts of these areas on Tuesday. Scattered to numerous strong rainshowers are within 120 nm of the center in the N semicircle. Scattered moderate to strong rainshowers are elsewhere within 150 nm of the center in the N semicircle, and within 120 nm of the center in the S semicircle. 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. The center of Tropical Storm Isaac at 11/0300 UTC is near 14.5N 46.9W. Isaac is moving W, or 270 degrees, 14 knots. The estimated minimum central pressure is 997 mb. The maximum sustained wind speeds are 60 knots with gusts to 75 knots. People who are in the Lesser Antilles should monitor the progress of ISAAC. Numerous strong rainshowers are within 20 nm of the center in the NE semicircle. 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. The center of Hurricane Helene at 11/0300 UTC is near 15.5N 32.4W. Helene is moving WNW, or 295 degrees, 10 knots. The estimated minimum central pressure is 968 mb. The maximum sustained wind speeds are 95 knots with gusts to 115 kt. Numerous strong rainshowers are within 60 nm of the center in the SW semicircle. Scattered moderate to isolated strong rainshowers are within 180 nm of the center in the N quadrant, and within 300 nm of the center in the S quadrant. 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. ...TROPICAL WAVES... No tropical wave is present at this time. ...MONSOON TROUGH/ITCZ... The monsoon trough is inland in Africa. The ITCZ is not analyzed at this time. Isolated moderate to locally strong rainshowers are elsewhere from 04N to 12N from 20W eastward, from 05N southward between 20W and 27W, and from 10N southward between 30W and 60W. ...DISCUSSION... GULF OF MEXICO... A narrow upper level trough extends from the NE corner of the Gulf of Mexico, to the east central Gulf of Mexico, to a cyclonic circulation center that about 150 nm to the north of the Yucatan Peninsula. The upper level trough is about 160 nm wide. Upper level cyclonic wind flow covers the Gulf of Mexico to the west of the trough. Upper level anticyclonic wind flow covers the Gulf of Mexico and the Atlantic Ocean to 70W, and the Caribbean Sea from 15N northward from 70W westward. Isolated moderate rainshowers are elsewhere in the Gulf of Mexico from 90W eastward. Please read the latest Tropical Weather Outlook, listed under WMO header ABNT20 KNHC, and under the AWIPS header MIATWOAT, for more details. The precipitation that currently is in the NW corner of the Caribbean Sea and the Yucatan Peninsula is showing some signs of organization. This system is forecast to move slowly northwestward across the Yucatan Peninsula today with limited development. Upper level winds are forecast to become more conducive for development later in the week. It is possible that a tropical depression may form on Thursday or Friday, while the disturbance moves across the western Gulf of Mexico. People who live in northeastern Mexico and the coast of Texas and Louisiana should monitor the progress of this system. Heavy rainfall and gusty winds are likely in western Cuba and the Yucatan Peninsula today. A frontal trough is in the Texas coastal plains/the Texas coastal waters. A separate surface trough is along the line from the SE part of Louisiana, to 27N93W and 25N93W. Isolated moderate rainshowers are from 23N northward from 90W westward. A surface trough in the western Caribbean Sea will move across the Yucatan peninsula on Tuesday, and into the Gulf of Mexico on Wednesday. The trough will move into the western Gulf on Thursday, and to the west of the area on Saturday. CARIBBEAN SEA... A surface trough extends from the SE Gulf of Mexico, through the Yucatan Channel, to a 1007 mb low pressure center that is near 23N84W, just to the north of the Gulf of Honduras. Numerous strong rainshowers are from 18N to the coast of NW Cuba between 82W and 86W. Numerous strong rainshowers also are inland, from 16N to 18N between 89W and 93W, covering the southern parts of the Yucatan Peninsula, Belize, Guatemala, and the Isthmus of Tehuantepec of southern Mexico. Other rainshowers also are in the NW corner of the Caribbean Sea, and parts of western Cuba, the Yucatan Peninsula of Mexico, and Central America from Honduras to El Salvador and Guatemala. The precipitation is showing some signs of organization in the northwestern Caribbean Sea. This system is forecast to move slowly northwestward across the Yucatan Peninsula today with limited development. Upper level winds are forecast to become more conducive for development later in the week. It is possible that a tropical depression may form on Thursday or Friday, while the disturbance moves across the western Gulf of Mexico. People who live in northeastern Mexico and the coast of Texas and Louisiana should monitor the progress of this system. Heavy rainfall and gusty winds are likely in western Cuba and the Yucatan Peninsula today. Isaac has weakened to tropical storm strength near 14.5N 46.9W 997 mb at 11 PM EDT moving W at 14 kt. Maximum sustained winds 60 kt gusts 75 kt. Isaac will move to 14.5N 49.0W Tue morning, then become a minimal hurricane near 14.6N 51.7W Tue evening. Isaac will continue to 14.8N 54.3W Wed morning, 15.0N 56.9W Wed evening. Isaac will weaken to a tropical storm near 15.4N 62.4W Thu evening, and continue weakening slowly as it moves to 15.5N 68.0W Fri evening and to 15.5N 72.5W Sat evening. ATLANTIC OCEAN... Please read the SPECIAL FEATURES section for details about Hurricane FLORENCE, Tropical Storm ISAAC, and Hurricane HELENE. An upper level trough extends from a 30N35W cyclonic circulation center, to 28N49W. Upper level cyclonic wind flow covers the Atlantic Ocean from 23N northward between 26W and 51W. Isolated moderate rainshowers are comparatively most prominent from 30N to 33N between 31W and 36W, and within 60 nm to 90 nm on either side of the line that runs from 20N52W 23N50W 26N48W. Rainshowers are possible elsewhere, in general, in the area of upper level cyclonic wind flow. Hurricane Florence near 25.9N 62.4W 944 mb at 11 PM EDT moving WNW at 11 kt. Florence will remain an extremely dangerous major hurricane through Thursday. Maximum sustained winds 120 kt gusts 145 kt. Florence will move to 26.5N 64.5W Tue morning, 27.9N 67.5W Tue evening, 29.6N 70.4W Wed morning, 31.3N 73.2W Wed evening, and pass north of the area to near 34.0N 76.5W Thu evening. For additional information please visit http://www.hurricanes.gov/marine $$ MT