180 AXNT20 KNHC 111225 AAA TWDAT Tropical Weather Discussion...Updated NWS National Hurricane Center Miami FL 825 AM EDT Tue Sep 11 2018 Updated Special Features section for Hurricane Florence 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 0600 UTC surface analysis and satellite imagery through 1200 UTC. ...SPECIAL FEATURES...Updated Hurricane Florence has weakened slightly as of 8 AM this morning. At 11/1200 UTC, Florence was centered near 26.4N 64.6W or 350 nm S of Bermuda and about 830 nm ESE of Cape Fear North Carolina moving WNW or 290 degrees at 13 kt. The estimated minimum central pressure is 950 mb. The maximum sustained winds have diminished slightly to 115 kt with gusts to 140 kt. Latest satellite imagery shows scattered moderate to strong convection within 150 nm of the center in the NE quadrant, and within 120 nm of the center in the SE quadrant. Scattered moderate convection is within 150 nm of the center in the SW quadrant, and within 180 nm of the center in the NW quadrant. Florence is forecast to continue on a west-northwestward to northwestward motion with a slight increase in forward speed are expected during the next couple of days. 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 on Thu. Interests elsewhere in the southeastern and mid-Atlantic states need to monitor the progress of Florence. 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 48.1W at 11/0900 UTC, which is about 765 nm E of the Lesser Antilles moving W or 270 degrees at 12 kt. The estimated minimum central pressure is 997 mb. The maximum sustained wind s are 60 kt with gusts to 75 kt. Latest satellite imagery shows scattered moderate convection within 90 nm of the center, except within 120 nm of the center in the SE quadrant. The present motion is expected to continue through the end of the week. On this track, Isaac should move across the Lesser Antilles and into the eastern Caribbean Sea on Thu. Interest in the Lesser Antilles should monitor the progress of 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. Hurricane Helene is centered near 16.0N 33.6W at 11/0900 UTC, which is about 540 nm west of the southernmost Cabo Verde Islands or 1365 nm south-southwest of the Azores moving WNW or 300 degrees at 12 kt. The estimated minimum central pressure is 968 mb. The maximum sustained winds are 95 kt with gusts to 115 kt. Latest satellite imagery shows scattered moderate convection within 120 nm of the center in the SE and NW quadrants and within 150 nm of the center in the NE and S quadrants and within 60 nm of the center in the SW quadrant. Scattered moderate convection is Helene is forecast to maintain its present motion with a decrease in forward speed through tonight. It is forecast to then turn toward the the northwest and then north-northwest on Wed and Thu. 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... Tropical waves are not presently being analyzed. ...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 northeastern part of the Gulf of Mexico to the eastern central Gulf of Mexico and to an upper-level low at 24N88W, It continues from the low to inland the eastern Yucatan Peninsula. Associated upper cyclonic flow is present south of 29N 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. Scattered moderate isolated strong convection is occurring to the southeast of the upper-level low over the southeastern gulf waters to the south of 25N east of 87W. Isolated showers and thunderstorms are elsewhere east of 91W. Please read the latest Tropical Weather Outlook under WMO header ABNT20 KNHC, and under the AWIPS header MIATWOAT for more details. The convection over southeastern Gulf of Mexico and the northwestern Caribbean Sea is showing signs of organization, but there are no signs of a surface circulation. Limited development is anticipated today, but upper-level winds are forecast to become more conducive, and a tropical depression could form on Thu or Fri while the disturbance moves across the western Gulf of Mexico. 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 likely over western Cuba and portions of the northeastern Yucatan Peninsula today. A stationary front is just inland the Texas coast and SW Louisiana. 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 west of 95W. Isolated showers and 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, through the Yucatan Channel and to a 1009 mb low over the Gulf of Honduras at 17N87W. Latest satellite imagery shows numerous moderate to strong convection north of 18N and west of 81W. Scattered showers and isolated thunderstorms are elsewhere north of 15N and west of 74W, including the Gulf of Honduras. The numerous to strong convection is showing signs of organization, but there are no signs of a surface circulation. Limited development is anticipated today, but upper-level winds are forecast to become more conducive, and a tropical depression could form on Thu or on Fri while the disturbance moves across the western Gulf of Mexico. Tropical Storm Isaac near 14.6N 48.1W 997 mb at 5 AM EDT is moving W at 12 kt, with maximum sustained winds of 60 kt gusts to 75 kt. Isaac will move to 14.6N 50.1W this afternoon, then become a minimal hurricane tonight near 14.6N 52.6W. Isaac will continue to 14.8N 55.0W Wed afternoon, then weaken back to a tropical storm near 15.1N 57.6W by late Wed night. Isaac will continue weakening as it tracks westward to near 15.5N 62.8W late Thu night, to near 15.6N 67.4W Fri night and to near 15.8N 72.0W Sat night. Expect winds and seas to increase over the far eastern Caribbean beginning late Wed into Thu. 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 an upper-level low at 30N35W southwestward to 26N40W, where it becomes a cyclonic shear axis to a small upper-level low dropping south at 26N48W and to near 23N55W. Upper-level cyclonic flow covers the area generally to the north of 23N between 26W and 54W. Scattered moderate convection is within 120 nm SE of the upper-level low at 26N48W, and within 60 nm of the upper-level low at 30N35W. Isolated showers and thunderstorms are from 22N to 24N between 44W and 50W. Isolated showers and thunderstorms are elsewhere west of 40W. Hurricane Florence near 26.4N 64.16 954 mb at 8 AM EDT is moving WNW at 13 kt, with maximum sustained winds of 115 kt with gusts to 140 kt. Florence will move to 27.2N 66.4W this afternoon, 28.7N 69.4W tonight, 30.5N 72.2W Wed afternoon, pass to the north of the area near 32.2N 74.5W Wed night, then approach the Carolina coast near 34.3N 77.1W Thu night. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre