365 AXNT20 KNHC 222353 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 753 PM EDT Wed Aug 22 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. ...TROPICAL WAVES... A far eastern Atlantic tropical wave has its axis along 27W from 07N-20N, moving westward at 10-15 kt. The wave is embedded within a very dry and stable environment inhibiting convection at this time. Only isolated weak showers and thunderstorms are seen within 120-180 nm east of the wave from 10N to 11N. A central Atlantic tropical wave has its axis extending along 46W from 05N-19N, moving westward at about 10 kt. This wave is also embedded within a very dry and stable environment caused by Saharan Air Layer outbreak of the past several days that is spreading westward across the central and eastern Atlantic. Scattered moderate convection is within 120 nm east of the wave from 08N to 10N. Isolated showers are south of 10N, where the wave meets the monsoon trough. An eastern Caribbean Sea tropical wave has its axis along 68W south of 19N to well inland Venezuela. It is moving westward near 15-20 kt. Scattered showers are increasing south of 10N over Venezuela. A west Caribbean tropical wave has its axis along 80W from 07N to 20N, moving westward near 15 kt. Previous deep convection with this wave has dissipated. Scattered moderate convection prevails south of 12N between 80W-84W. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from the African coast near 12N17W to 09N44W. The ITCZ axis begins at 09N44W and continues to 10N55W. Scattered moderate convection is within 120 nm of the ITCZ. ...DISCUSSION... GULF OF MEXICO... High pressure of 1021 mb is analyzed near 26N95W, while a surface trough extends from southeastern Georgia southwestward to the northeastern gulf and continues to near 27N91W. The nocturnal Yucatan Peninsula trough has moved across the southwestern gulf during the late night and early morning hours, and is analyzed from near 21N96W to 18N94W. The present pressure gradient across the gulf generally supports light to gentle winds throughout, except for gentle to moderate winds south of 26N and relatively low seas of 1 to 3 ft. Scattered showers and thunderstorms are observed over the far southwest section of the gulf south of 21N and west of 94W in association with the nocturnal trough that moved offshore the Yucatan Peninsula during the overnight hours. Other scattered showers and thunderstorm activity continues to increase over the north-central gulf in association with the aforementioned surface trough, with further support from an upper- level trough that is dropping southward across the norther gulf section. The activity over the far southwest is expected to weaken during the afternoon. It should then re-develop tonight and Thu night as the surface trough again moves across those same waters. The activity over the north- central gulf should continue to increase through this afternoon and into the evening hours. Otherwise, relatively weak high pressure ridging will remain across the northern gulf waters, with the associated gradient producing gentle to moderate anticyclonic flow through Fri. CARIBBEAN SEA... Two tropical waves are moving across the basin. Refer to the section above for details. An upper level trough extends from eastern Cuba southwestward to just east of northeastern Honduras. Water vapor imagery indicates plentiful deep layer moisture along and to the northwest of this trough, and it is where isolated showers and thunderstorms are occurring. Scattered moderate isolated strong convection has increased over the far southwestern Caribbean south of 11N between 77W and 82W mainly due to low-level wind speed convergence, with the added factor of the eastern segment of the eastern Pacific monsoon trough that stretches east- northeastward to the far southwestern Caribbean along 09N and to the typical climatological low found over northwestern Colombia presently located just offshore that coast at 09N76W. A slighter tighter pressure gradient behind the tropical wave along 77W will help induce strong to near gale force northeast to east trade winds over the south-central Caribbean waters off the coast of Colombia and across the Gulf of Venezuela tonight. The strong trades are forecast to reach northward to 15N. Moderate to fresh trades will continue elsewhere through Fri as little overall changes are expected with the present synoptic set-up through Fri. ATLANTIC OCEAN... Two tropical waves are moving across the basin. Refer to the section above for details. A surface trough is analyzed from 29N61W to 21N68W. A shear axis is evident by model and satellite winds to be situated northwest of the trough from 32N65W to 25N70W to east-central Cuba. Satellite imagery shows increasing scattered showers and thunderstorms within 180 nm to the northwest of the trough between 65W and 69W. Isolated showers and thunderstorms are seen over the western portion of the basin west of about 75W. This activity as well as that to the northwest of the surface trough are expected to last through tonight and into Thu. Another trough moving westward around 15 kt is along 52W from 17N to 30N. No deep convection is noted with this trough, only isolated showers within 120 nm east of the trough from 21N to 26N. A 1025 mb high center is analyzed north of 31N and extends a ridge across the remainder of the basin. Saharan dust and associated dry air, although not as dense as in previous days, is noted mainly east of about 60W on GOES-16 GEO color dust imagery. The dust is keeping convection rather limited, to non-existent, outside across the eastern and central Atlantic waters, except as described above near the the ITCZ region. For additional information please visit http://www.hurricanes.gov/marine $$ JA/ERA