117 AXNT20 KNHC 110005 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 805 PM EDT Mon Sep 10 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 2345 UTC. ...SPECIAL FEATURES... The center of Hurricane Florence at 10/2100 UTC is near 25.4N 61.1W. Florence is moving WNW, or 285 degrees, 11 knots. The estimated minimum central pressure is 939 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 by Tuesday morning. Numerous strong rainshowers are within 90 nm of the center in the NW semicircle. Scattered moderate to isolated strong rainshowers are elsewhere from 21N to 28N between 54W and 62W. 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 Hurricane Isaac at 10/2100 UTC is near 14.4N 45.0W. Isaac is moving W, or 270 degrees, 12 knots. The estimated minimum central pressure is 993 mb. The maximum sustained wind speeds are 65 knots with gusts to 80 knots. People who are in the Lesser Antilles should monitor the progress of ISAAC. Numerous strong rainshowers are within 75 nm of the center in the W semicircle, and within 45 nm of the center in the E semicircle. Scattered moderate to strong rainshowers are from 12N to 14N between 41W and 44W. Anyone who is in the area of the Lesser Antilles should monitor the progress of Hurricane Isaac. 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 10/2100 UTC is near 14.9N 31.5W. Helene is moving WNW, or 290 degrees, 12 knots. The estimated minimum central pressure is 974 mb. The maximum sustained wind speeds are 90 knots with gusts to 110 kt. Numerous strong rainshowers are within 135 nm of the center in the NW quadrant and in the SW quadrant. Widely scattered moderate to isolated strong rainshowers are elsewhere from 09N to 17N between 22W and 31W. 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. along 08N48W 06N54W 07N58W. Isolated moderate to locally strong rainshowers are elsewhere from 10N southward from 20W eastward, and to the south of Hurricane Isaac and Hurricane Helene from 06N to 10N between 34W and 45W. Rainshowers are possible elsewhere from 10N southward from 60W eastward. ...DISCUSSION... GULF OF MEXICO... An 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 is just to the north of the Yucatan Peninsula. Upper level cyclonic wind flow covers the Gulf of Mexico east of 92W. Upper level anticyclonic wind flow covers the rest of the area. Widely scattered moderate to isolated strong rainshowers are to the east of 90W. This area of precipitation is forecast to move slowly northwestward near the Yucatan Peninsula on Tuesday with limited development expected. Upper level winds are forecast to become more conducive for development on Wednesday, when the system moves across the southern Gulf of Mexico. It is possible that a tropical depression may form on Thursday or Friday, while the disturbance moves across the western Gulf of Mexico. Please read the latest Tropical Weather Outlook for more details, TWOAT/ABNT20 KNHC. A frontal trough is in the Texas coastal plains/the Texas coastal waters. Isolated moderate rainshowers are to the west of the line that runs from SE Louisiana to the coast of Mexico near 20N96W. A surface trough in the western Caribbean will move across the Yucatan peninsula Tue, and into the Gulf of Mexico Wed. The trough will move into the western gulf Thu, and west of the area Sat. CARIBBEAN SEA... Upper-level cyclonic flow associated with the upper low over the Gulf of Mexico near 25N88W covers the northwestern Caribbean Sea as well as western and central Cuba. A weak surface trough is analyzed from near 21N82.5W to near just northeast of the northeastern coast of Honduras. Scattered moderate to strong convection increasing in coverage is observed to the north of 17N west of 79W to juts inland the coast of the Yucatan Peninsula. This activity is quickly lifting northward under moderate to strong upper-level southerly flow located to the east of the Gulf of Mexico upper-level low near 25N88W. Satellite imagery indicates that this activity is showing signs of organization, and it is forecast to move slowly northwestward near the Yucatan Peninsula on Tue with limited development expected. Upper-level winds are forecast to become more conducive for development on Wed when the system moves over the southern Gulf of Mexico. Rainshowers that are in NW corner of the Caribbean Sea, western Cuba, the Yucatan Peninsula of Mexico, and Central America from Honduras to El Salvador and Guatemala, are associated with a surface trough, and are showing some signs of organization. This system is forecast to move slowly northwestward across the Yucatan Peninsula on Tuesday 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 are in NE Mexico and the coast of Texas and Louisiana should monitor the progress of this system. It is likely that heavy rainfall and gusty winds will be present in western Cuba and the Yucatan Peninsula through Tuesday. Hurricane Isaac near 14.4N 45.0W 993 mb at 5 PM EDT moving W at 12 kt. Maximum sustained winds 65 kt gusts 80 kt. Isaac will move to 14.5N 47.1W Tue morning, 14.6N 49.8W Tue afternoon, 14.6N 52.3W Wed morning, 14.8N 54.7W Wed afternoon, and 15.3N 60.2W Thu afternoon. Isaac will weaken to a tropical storm near 15.5N 65.5W Fri afternoon, and change little in intensity as it moves to 15.5N 70.5W Sat. ATLANTIC OCEAN... Please read the SPECIAL FEATURES section for details about Hurricane FLORENCE, Hurricane ISAAC, and Hurricane HELENE. A surface trough is analyzed from 32N61W to 29N65W. Upper-level cyclonic flow is present to the north of 27N between 67W and 74W attributed to an upper low moving westward near 29N74W. Broad anticyclonic is west of 74W due to the upper-level low in the Gulf of Mexico near 24N88W. Water vapor imagery shows mid to upper-level clouds streaming northeastward and eastward over the western half of the area. These clouds are originating from the deep convective activity that is occurring over the southeastern Gulf of Mexico as described above. Otherwise, isolated showers and thunderstorms are west of 65W. A weak 1017 mb high center is analyzed at 26N73W, with a ridge southwestward to the Straits of Florida. The associated weak gradeint is allowing for generally light to gentle winds to exist over the western half of the area. Expect for these conditions to continue through Wed, except in the northeastern section the the TAFB forecast offshore waters zones where Hurricane Florence is forecast to track across. Below is the latest forecast for Florence bases on the 15Z NHC advisory. Hurricane Florence near 25.4N 61.1W 939 mb at 5 PM EDT moving WNW at 11 kt. Maximum sustained winds 120 kt gusts 145 kt. Florence will move to 26.0N 63.2W Tue morning, 27.0N 66.2W Tue afternoon, 28.6N 69.3W Wed morning, 30.4N 72.2W Wed afternoon, and move north of the area to near 33.7N 77.0W Thu afternoon. For additional information please visit http://www.hurricanes.gov/marine $$ ja/al/mt