928 AXNT20 KNHC 171206 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 806 AM EDT Fri Aug 17 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 0600 UTC surface analysis and satellite imagery through 1145 UTC. ...SPECIAL FEATURES... The center of Tropical Storm Ernesto at 17/0900 UTC is near 45.6N 36.4W or 620 nmi to the NW of the Azores. Ernesto is moving NE at 22 knots. The estimated minimum central pressure is 1006 mb. The maximum sustained wind speeds are 40 knots with gusts to 50 knots. Scattered moderate convection is from 44N to 48N between 30W and 37W. Ernesto is expected to become a post-tropical cyclone by tonight and then become extratropical as it merges with a frontal zone on Saturday. Ernesto will approach Ireland and the United Kingdom on Saturday. Please read the latest NHC forecast/advisory under AWIPS/WMO headers MIATCPAT5/WTNT35 KNHC for more details. ...TROPICAL WAVES... A tropical wave is in the E Atlc with axis extending from 05N-17N along 29W, moving W at 10-15 kt. The wave is in a moderate deep layer wind shear environment, and both CIRA LPW and GOES-16 water vapor imagery at the lower levels show dry air affecting the wave. These two factors are contributing to the lack of convection at this time. A tropical wave is in the central Atlc with axis extending from 06N-20N along 54W, moving W at 15-20 kt. The wave is in a low deep layer wind shear environment, and CIRA LPW imagery shows abundant low level moisture associated with it. However, some dry air intrusion is noted in the NW wave environment shown both in CIRA LPW and water vapor imagery at the lower levels. This dry air has acted to reduced the convection to scattered moderate isolated strong from 10N-15N between 50W-60W. A tropical wave is in the central Caribbean with axis extending from 11N-20N along 70W, moving W at 10-15 kt. The wave is in a moderate to strong deep layer wind shear environment. GOES-16 water vapor imagery at the lower levels show very dry air over this region of the Caribbean. This is limiting convection to isolated showers and tstms over Hispaniola adjacent waters. A tropical wave is the SW Gulf of Mexico with axis S of 21N along 92W, moving W at 10-15 kt. Both CIRA LPW and GOES-16 water vapor imagery at the lower levels show dry air over this region, which is limiting convection to isolated showers in the Bay of Campeche. ...MONSOON TROUGH/ITCZ... The monsoon trough extends from the coast of W Africa near 11N16W to 08N21W to 07N30W. The ITCZ begins near 07N30W and continues to 06N40W to 06N50W. Scattered moderate isolated strong convection is from 04N-07N E of 20W. For more information about convection, see the tropical waves section. ...DISCUSSION... GULF OF MEXICO... Upper level cyclonic wind flow covers the SW corner of the Gulf of Mexico from 23N southward from the Yucatan Channel westward. Warming cloud top temperatures and weakening convective precipitation, and lingering widely scattered moderate to isolated strong rainshowers are in the Gulf of Mexico and the coastal plains of the western part of the Yucatan Peninsula from 21N southward between land and 93W. A surface ridge extends from a 1025 mb high pressure center that is near 31N69W, across Florida just to the north of Lake Okeechobee, into the east central Gulf of Mexico, to the coast of Mexico along 20N in the SW corner of the Gulf of Mexico. Isolated moderate to locally strong rainshowers are in the waters from 23N northward from 90W eastward. An east-to-west oriented surface ridge extends across the Gulf waters along 28N. The ridge is accompanied by gentle to moderate anticyclonic wind flow, that is expected to increase to a fresh southerly breeze across the northwest waters, from Sunday night through early Monday. A surface trough will develop along the Yucatan Peninsula during the late afternoons, then drift westward across the SW Gulf waters during the overnight hours. The trough will be accompanied by a fresh east-to-southeast wind shift, with the trough dissipating along 96W during the late mornings. CARIBBEAN SEA... Isolated moderate to locally strong rainshowers cover the NW corner of the Caribbean Sea, from 14N northward from 79W westward. Upper level anticyclonic wind flow covers the Caribbean Sea from the Windward Passage westward. Nocturnal near gale force easterly trade winds are expected along the northwest coast of Colombia overnight, and then again on Friday night. A tropical wave along 68W will continue westward across the central Caribbean tonight, and pass through the western Caribbean waters during the upcoming weekend. A second tropical wave will reach along 55W on Friday, and pass through the eastern Caribbean Sea on Saturday and Sunday. The tropical wave will be accompanied by locally strong rainshowers through early Saturday. ATLANTIC OCEAN... An upper level trough passes through 32N37W, to 27N44W, to an Atlantic Ocean cyclonic circulation center that is near 25N53W. A surface trough is along 32N55W 28N57W 25N60W. Isolated moderate to locally strong rainshowers are from 30N northward between 44W and 57W. Rainshowers are possible elsewhere from 20N northward between 30W and 60W. Surface anticyclonic wind flow is on either side of the 32N55W-to-25N60W surface trough. Broad upper level cyclonic wind flow, and isolated moderate rainshowers, cover the Atlantic Ocean from the Greater Antilles northward from 60W westward. A few individual cyclonic circulation centers near 27N63W, and near 21N70W. An east to west ridge extends from 30N65W to 28N81W. Light southerly winds are to the north of the ridge. Fresh trade winds are to the south 23N, except becoming locally strong along the north coast of Hispaniola during the late afternoon into early evening hours. For additional information please visit http://www.hurricanes.gov/marine $$ MT/NR