000 AXNT20 KNHC 170605 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 205 AM EDT Thu Aug 17 2017 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 0545 UTC. ...SPECIAL FEATURES... Hurricane Gert is centered near 40.1N 58.4W at 17/0300 UTC or about 350 nm SE of Halifax Nova Scotia and about 460 nm SSW of Cape Race Newfoundland moving ENE at 32 kt. Estimated minimum central pressure is 967 mb. Maximum sustained wind speed is 90 kt with gusts to 110 kt. Numerous moderate convection and scattered tstms are from 37N-42N between 54W-59W. Scattered moderate convection is elsewhere from 36N-46N between 50W-60W. See latest NHC forecast/ advisory under AWIPS/WMO headers MIATCMAT3/WTNT23 KNHC for more details. A 1011 mb low is located about 560 nm east of the Lesser Antilles near 13N50W. Intrusion of Saharan dry air and dust to its environment is noticed in GOES-16 experimental imagery and CIRA LPW imagery, however the system looks a little more concentrated. This being favored in part by low vertical wind shear. Scattered moderate convection and isolated tstms are within 220 nm W semicircle from low center. Isolated showers are within 220 nm SE quadrant of the low. Upper-level winds are forecast to become more conducive for development during the next day or so while the low moves westward across the tropical Atlantic Ocean, crossing into the Caribbean Sea on Friday. Regardless of development, locally heavy rainfall and gusty winds are expected to spread across portions of the Lesser Antilles on Thursday night and Friday. This system has a medium chance of becoming a tropical cyclone in the next two days. A tropical wave is in the central Atlc associated with a 1009 mb low pressure located near 14N38W. The wave axis extends from 21N38W to the low and has been moving W at 15 kt. The wave is in a region of low to moderate vertical wind shear, however intrusion of Saharan dry air and dust to the wave environment limit convection to scattered moderate within 245 nm W semicircle of low pressure center. Gradual development of this system is possible during the next few days while it moves WNW, but upper- level winds are expected to become less conducive for tropical cyclone formation when the disturbance moves north of the Leeward Islands this weekend. This system has a medium chance of becoming a tropical cyclone in the next two days. ...TROPICAL WAVES... A tropical wave is in the E Atlc associated with a 1013 mb low near 08N20W. The wave axis extends from 18N18W to the low center. The CIRA LPW imagery show dry air intrusion to the wave environment, which has significantly reduced the convection this wave had when it was coming off the W African coast yesterday. GOES-16 experimental and Meteosat SAL imagery show Saharan dust and dry air engulfing this wave. Monsoon moisture and middle to upper level diffluent flow support scattered moderate convection and isolated tstms from 06N to 15N E of 25W. Environmental conditions are forecast to become more conducive for development over the weekend while the system moves WNW. A tropical wave is in the E Caribbean with axis extending from 23N61W to 12N66W, moving W at 15-20 kt. There is abundant moisture associated with this wave that along with upper level divergent flow support scattered to isolated moderate convection and tstms from 16N to 24N between 61W and 69W, including Puerto Rico. A tropical wave is in the W Caribbean with axis extending from 19N85W across Honduras to 10N87W, moving W at 20 kt. The wave is in a region of low vertical wind shear, however dry air subsidence continue to limit convection to isolated showers within 90 nm of its axis. ...ITCZ/MONSOON TROUGH... The monsoon trough extends from the African coast near 11N16W to 09N30W. To the west, the monsoon trough and ITCZ is disrupted due to the tropical lows and tropical waves mentioned above. Otherwise, scattered moderate convection is from 05N-09N between 25W-45W. ...DISCUSSION... GULF OF MEXICO... Except for scattered showers over the E Bay of Campeche associated with a surface trough along 93W, the remainder basin in under the influence of a surface ridge anchored by a 1019 mb high near 28N85W. This setup is prividing ESE gentle to moderate flow across the northern half of the Gulf, except for light to gentle variable flow in the NE basin around the high center. Otherwise, NE fresh winds are off the W Yucatan Peninsula coast associated with the surface trough. The high is expected to persist across the NE Gulf waters through early Saturday. A surface trough will develop each evening across the Yucatan peninsula shifting W into the Bay of Campeche during the overnight hours. Locally higher winds can be expected in the vicinity of the trough axis. CARIBBEAN SEA... A tropical wave is moving across the NW basin and Honduras supporting isolated showers. A second tropical wave is in the E Caribbean with axis near 64W, which is supporting scattered to isolated showers and tstms over the NE basin including Puerto Rico, the Mona Passage and the Virgin Islands. See tropical waves section for further details. Genearally, diffluent flow is obserseved in the SW Caribbean, which is supporting scattered showers S of 13N W of 70W. Lastly, a diffluent flow pattern persist between an upper level ridge anchored over S Georgia and a low centered N of the Windward Passage. This continue to support scattered to isolated showers across central Cuba. Otherwise, dry air subsidence and strong vetical wind shear support fair weather elsewhere W of 70W. Fresh to strong winds in the south-central waters and in the vicinity of the tropical wave in the eastern waters are expected through Thursday with moderate to fresh trades elsewhere. ...HISPANIOLA... An upper level low is centered N of the Windward Passage ahead of a tropical wave that is forecast move over the central Caribbean Thursday. The approaching wave is already supporting isolated showers over the Dominican Republic, but the activity will increase during Thursday and into early Friday. ATLANTIC OCEAN... The basin N of 23N continue under the influence of the Azores subtropical high which supports fair weather. For information about tropical waves, see sections above. For additional information please visit http://www.hurricanes.gov/marine $$ Ramos