000 AXNT20 KNHC 150005 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 805 PM EDT Fri Jul 14 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 1800 UTC surface analysis and satellite imagery through 2345 UTC. ...TROPICAL WAVES... A central Atlantic tropical wave has its axis along 43W/44W south of 15N, moving westward 20 knots. The majority of the wave is shrouded by dry Saharan air as depicted in the latest METEOSAT-9 Saharan Air Layer imagery. Only convection noted with this wave is south of 10N to the ITCZ region, and consists of the scattered moderate type intensity convection from 07N to 10N between 42W-45W. A Caribbean Sea tropical wave has its axis along 63W/64W south of 18N. This wave is moving westward at an estimated speed of 19 kt over the past 24 hours. The wave exhibited a well pronounced northeast to southeast wind shift in the upper air sounding from Trinidad this morning at 12Z. Last visible satellite imagery continued to show a pretty well-defined cloud structure to the wave, with what appears to be a low-level vorticity maximum on the southern portion of the wave axis at 12.5N64W. Scattered moderate convection is within 30 nm of 14N64W. Scattered showers and isolated thunderstorms are elsewhere east of the wave axis. This wave is forecast to move across the rest of the eastern Caribbean through Saturday and reach the central Caribbean by Saturday evening. Increasing moisture along scattered showers and isolated thunderstorms will follow the wave. Some of the shower and thunderstorm activity may contain gusty winds. A central Caribbean Sea tropical wave has its axis along 74W, moving westward at about 15 knots. The northern portion of the wave axis is just west of Haiti. A small upper low is noted over the northern part of the wave, with an associated trough extending from it over the remainder of the wave. Subsidence aloft with dry is over the this wave's environment for the time being. Deep convection that occurred during this afternoon just east of the wave has dissipated. Only isolated showers and thunderstorms are within 150 nm east and 60 nm west of the wave axis north of 15N. The wave will move across the rest of the central Caribbean through early Saturday and the western portion of the sea later on Saturday and through Sunday. The wave may acquire more in the way of moisture along with shower and thunderstorm activity as it moves through the western Caribbean. ...ITCZ/MONSOON TROUGH... The Monsoon Trough axis extends from passes through coastal sections of Guinea-Bissau near 12N16W and continues to 11N22W where scatterometer data indicates the ITCZ then begins and continues to 08N34W to 06N40W to just west of the tropical wave along 43W/44W. It resumes just west of the same wave to near 06N54W. Scattered moderate isolated strong convection is within 120 nm south of the axis between 52W-54W. Scattered moderate convection is within 180 nm north of the axis between 37W-42W and within 240 nm north of the axis between 45W-48W. ...DISCUSSION... ...THE GULF OF MEXICO... A weak pressure pattern is present across the area. A small upper low is noted just northwest of the Yucatan Peninsula with a trough reaching to the north-central Gulf near southeastern Louisiana. A very moist and unstable air mass in place over just about the entire Gulf, except in the far SW Gulf where some dry air is noted aloft. A surface trough, most likely a result of the upper trough, is analyzed from near 29N87W to 24N86W. Scattered showers and thunderstorms are occurring north of 24N east of 92W, while scattered showers and isolated thunderstorms are north of 24N west of 92W. Isolated showers and thunderstorms are south of 92W. Isolated showers are south of 24N and west 92W. Moisture guidance suggests that ample moisture will continue over much of the Gulf through the weekend maintaining good chances for more scattered shower and thunderstorm activity. ...THE CARIBBEAN SEA... A couple of tropical wave are moving through the Caribbean Sea. See above for details on these features. The pressure gradient throughout remains fairly weak. A small upper level low is just south of Haiti, with a sharp upper trough extending from it to the coast of Colombia near 11N71W. A small upper level anticyclone is over the far SW Caribbean Sea near 11N80W. Broad anticyclonic flow covers the western Caribbean, and the eastern part of the sea to the east of the upper trough. The far NW Caribbean is under the eastern fringe of upper cyclonic flow related to the upper low that is situated just northwest of the Yucatan Peninsula. The anticyclonic flow over the eastern Caribbean is transporting upper debris clouds attributed to the convective activity east of the eastern Caribbean wave north-northeastward towards the NE Caribbean and Leeward Islands. Abundant moisture over the western Caribbean is producing scattered showers and isolated thunderstorms there, including the far SW Caribbean where the eastern segment of the eastern Pacific monsoon trough is analyzed across Costa Rica and Panama. ...HISPANIOLA... Deep convection that earlier occurred with the tropical wave that is just west of Haiti has dissipated, however, deep convection remains over much of the northwestern section of Hispaniola. Isolated showers and weakening are elsewhere over the island and nearby waters. Moisture associated with the eastern Caribbean wave will begin to approach the eastern part of the Hispaniola on Saturday afternoon, and spread across the remainder of the island into Sunday. With this scenario expected, shower and thunderstorm activity should become more widespread over portions of the island as well as over the nearby waters. ...THE ATLANTIC OCEAN... A nearly stationary upper level low is seen near 28N65W, with a trough stretching from it southwestward to 24N66W to 22N76W to western Cuba. Another upper level low, this one is larger, is over the eastern Atlantic near 28N43W and is moving westward. A trough extends from this low southwestward to 21N46W and southward to a weak and small upper low near 17N47W. Upper level moisture, in the form of scattered to broken high clouds, is streaming northeastward from the eastern Caribbean Sea in southwesterly to westerly flow between the upper low near 28N65W and the anticyclonic flow over the eastern Caribbean Sea associated with a small anticyclone near 15N58W. Abundant dry air covers the central and eastern Atlantic as observed in water vapor imagery, and is confirmed by the Meteosat-9 imagery that depicts abundant dry and stable air over those portions of the Atlantic. It is also where an extensive Saharan Air layer is present with dust. At the surface, a nearly stationary 1028 mb high center analyzed 34N48W extends a ridge southwestward to 32N67W and to just east of northeastern Florida. A surface trough is along a position from 29N71W to 24N74W. The northern portion of the Caribbean tropical wave along 74W extends northward to the SE Bahamas. Scattered showers and thunderstorms are observed south of 26N between 68W- 75W, and also north of 25N between 57W-62W. Scattered showers and isolated thunderstorms are elsewhere south of 30N between 56W- 70W, and south of 28N between 62W-77W. Isolated showers and thunderstorms are noted over the remainder of the area west of 56W. The northern portion of the tropical wave will move across the rest of the southern Bhamas through Saturday, and across the far southwestern waters late Saturday through Sunday, while the ridging changes little. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre