100 AXNT20 KNHC 150537 AAA TWDAT Tropical Weather Discussion...Updated NWS National Hurricane Center Miami FL 137 AM EDT Sat Sep 15 2018 Updated Special Features section for Florence and Helene latest information 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 0515 UTC. ...SPECIAL FEATURES...Updated Tropical Storm Florence is centered near 33.9N 78.8W at 15/0000 UTC, or about 10 nm NNE of Myrtle Beach South Carolina moving W at 3 kt. Estimated minimum central pressure is 975 mb. Maximum sustained winds are 60 kt with gusts to 75 kt. Latest satellite imagery shows that Florence is exhibiting a rather symmetrical cloud pattern. Scattered moderate to isolated strong convection is within 180 nm of the center in the NE quadrant and within 120 nm of the center in the SE quadrant. Scattered moderate convection within an outer rainband is within 30 nm of a line from 33N79W to 34N81W and to 36N81W. Latest NHC advisory has Florence moving in a slow westward to west- southwestward expected motion though Sat. On the forecast track, the center of Florence will move farther inland across extreme southeastern North Carolina this evening, and across extreme eastern South Carolina tonight and Sat. Florence will then move generally northward across the western Carolinas and the central Appalachian Mountains early next week. The PUBLIC ADVISORIES for Florence are transmitted via the WMO header WTNT31 KNHC, and via the AWIPS header MIATCPAT1. The FORECAST/ADVISORIES for Florence are transmitted via the WMO header WTNT21 KNHC, and via the AWIPS header MIATCMAT1. Tropical Storm Helene is centered near 34.9N 36.4W at 15/0000 UTC, or about 510 nm WSW of Lajes Air Base In The Azores moving N at 16 kt. Estimated minimum central pressure is 988 mb. Maximum sustained winds are 60 kt with gusts to 75 kt. Latest satellite imagery shows scattered moderate convection from 35N to 39N between 31W and 39W. Helene is forecast to move toward the north through tonight, with a turn toward the north- northeast expected early Sat followed by a turn toward the northeast by Sun morning. On the forecast track, Helene will pass near or over the Azores late Sat or Sun. The PUBLIC ADVISORIES for Helene are transmitted via the WMO header WTNT33 KNHC, and via the AWIPS header MIATCPAT3. The FORECAST/ADVISORIES for Helene are transmitted via the WMO header WTNT23 KNHC, and via the AWIPS header MIATCMAT3. Tropical Storm Joyce is centered near 31.4N 44.1W at 14/2100 UTC, or about 930 nm WSW of the Azores moving SE at 5 kt. Estimated minimum central pressure is 1002 mb. Maximum sustained winds are 40 kt with gusts to 50 kt. Latest satellite imagery shows increasing convection, with a vigorous band now near the center in the northern semicircle. The convection consists of the scattered moderate type intensity within 180 nm of the center in the NE quadrant, and within 90 nm of the center in the NW quadrant. Scattered showers and thunderstorms are within 30 nm of a line from 30N47W to 30N44W to 31N42W. Joyce is forecast by the latest NHC advisory to turn northeastward with an increase in forward speed during the next 24 hours, followed by an eastward turn after 48 hours. The PUBLIC ADVISORIES for Joyce are transmitted via the WMO header WTNT3S KNHC, and via the AWIPS header MIATCPAT5. The FORECAST/ADVISORIES for Joyce are transmitted via the WMO header WTNT25 KNHC, and via the AWIPS header MIATCMAT5. Tropical Storm Isaac regained tropical storm status this afternoon and is centered near 15.3N 68.2W at 14/2100 UTC, or about 220 nm SSE of Santo Domingo Dominican Republic moving W at 12 kt. Estimated minimum central pressure is 1002 mb. Maximum sustained winds are 35 kt with gusts to 45 kt. Latest satellite imagery shows scattered moderate convection removed from the center from 12N to 15.5N between 68W and 71W. Scattered moderate convection is also seen to the east of Isaac from 14N to 17N between 64W and 66W. Isaac is forecast by the Latest NHC advisory to decrease its forward speed over the next couple of days with a turn to the west-northwest possible by late on Sun. On the forecast track, Isaac will move over the eastern and central Caribbean Sea during the next few days, and be near or south of Jamaica early next week. The PUBLIC ADVISORIES for Isaac are transmitted via the WMO header WTNT34 KNHC, and via the AWIPS header MIATCPAT4. The FORECAST/ADVISORIES for Isaac are transmitted via the WMO header WTNT24 KNHC, and via the AWIPS header MIATCMAT4. ...TROPICAL WAVES... A far eastern Atlantic tropical wave has its axis along 30W from 08N to 21N, moving westward at 10 to 15 kt. The wave is surrounding by a rather dry environment, which is inhibiting deep convection from forming along or near it. Only isolated showers and weak isolated thunderstorms are within 120 nm either side of the wave axis where it cross the monsoon trough. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from near 12N16W to 09N25W to 08N32W. The ITCZ continues from 08N32W to 09N41W to 10N46W to 12N57W. Aside from the shower and thunderstorm activity associated with the tropical wave along 30W, scattered moderate isolated strong convection is within 180 nm south of the ITCZ from 43W to 53W. Scattered moderate convection is within 180 nm south of the monsoon trough from 18W to 23W, and within 180 nm south of the ITCZ between 39W and 43W. ...DISCUSSION... GULF OF MEXICO... An upper-level cyclonic circulation center is over north-central gulf near 27N88W, with an inverted trough to an upper low over the northwestern Caribbean at 20N84W that is moving westward. Upper- level cyclonic wind flow covers the central part of the gulf. A surface trough extends from inland central Texas to a 1009 mb low along the coast just north of Brownsville and to 24N97W to 21N97W. Scattered moderate isolated strong convection is seen from 22N to 29N west of 92W. Isolated showers and thunderstorms cover the rest of the gulf. Heavy rainfall and gusty winds are likely to continue across portions of Texas and northeastern Mexico through Sat. A NW-to-SE orientated surface ridge will set up from central Louisiana to Florida Bay tonight. A surface high pressure center will develop along the ridge near 27N92W late on Saturday. The surface high will shift slightly southward on Sunday, and the ridge will extend southeastward to the Yucatan Basin. A weak surface trough, extending southwestward from the remnants of tropical cyclone Florence, will pass eastward, slowly, across the north central Gulf waters through early next week. CARIBBEAN SEA... Please refer to the the Special Feature section above for details on Tropical Depression Isaac. An upper level cyclonic circulation center is about 100 nm to the west of Jamaica, in the NW corner of the Caribbean Sea. Isolated showers and thunderstorms are north of 15N and west of 80W. Tropical Depression Isaac near 14.9N 67.3W 1007 mb at 11 AM EDT moving W at 14 kt. Maximum sustained winds are 30 kt gusts 40 kt. Isaac will move to 15.0N 69.0W this evening, 15.1N 71.3W Sat morning, 15.2N 73.3W Sat evening, 15.6N 75.3W Sun morning, 17.0N 79.5W Mon morning and dissipate early Tue. The highest winds and seas are expected mainly north of the center. Expect gentle to moderate trade winds elsewhere, to the west of Isaac. Moderate to locally fresh trade winds are forecast to the east of Isaac. Strong nocturnal trade winds are forecast off the northwest coast of Colombia on Monday night and on Tuesday night. ATLANTIC OCEAN... Please read the Special Features section, for details on Tropical Storm Florence, Tropical Storm Helene, and Tropical Storm Joyce. An upper-level trough extends from near 32N45W to 26N48W to 20N54W, and to 16N59W. Upper level cyclonic wind flow is within 360 nm on either side of the trough. Scattered showers and isolated thunderstorms are within 30 nm ether side of a line from 22N44W to 22N50W to 22N57W. Isolated showers and thunderstorms are seen elsewhere to the west of 56W. Tropical Storm Isaac near 15.3N 68.2W 1002 mb at 5 PM EDT moving W at 12 kt. Maximum sustained winds 35 kt gusts 45 kt. Isaac will move to 15.4N 70.1W Sat morning, 15.4N 72.2W Sat afternoon, 15.7N 74.2W Sun morning, weaken to a tropical depression near 16.2N 76.3W Sun afternoon, and 17.5N 80.0W Mon afternoon. Isaac will dissipate Tue afternoon. The highest winds and seas are expected mainly north of the center. A surface ridge will remain about stationary from near 32N68W to southeastern astern Florida through Sun. The ridge will shift northward, to a position from 31N74W to central Florida by the middle of the next week. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre