000 AXNT20 KNHC 170003 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 803 PM EDT Sun Jul 16 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 far eastern Atlantic tropical wave was introduced to the surface analysis this afternoon roughly along a position from 16N27W to 09N28W based on low to mid-level satellite winds, the Total Precipitable Water (TPW) imagery loop from a 24 hour period, and on mid-level potential vorticity and wind model guidance. The wave is moving westward about 10-15 kt, and is mostly embedded in deep tropical moisture that is associated with the monsoon trough segment that extends from West Africa to the the far eastern Atlantic. The latest TPW loop animation and METEOSAT-9 imagery both depict the moisture around this wave. Deep convection associated with the wave consists of the scattered moderate type intensity within 150 nm west of the wave along and near the monsoon trough from 09N to 11N. The latest data from the METEOSAT imagery does show extensive Saharan dust covering the eastern Atlantic section from just over the far northern part of the wave, and also well to the north and northeast of the wave. A central Atlantic tropical wave has its axis extending from near 15N49W to 11N50W and to 04N50.5W, moving westward near 7 kt. This wave marks the leading edge of a broad area of low pressure that encompasses the monsoon trough and covers the area well to the east of the wave to 40W and from 07N to 14N. At 1800 UTC, a 1011 mb low is analyzed near 10.5N46W moving generally westward near 13 kt. The CIRA moisture guidance depicts very a very deep moisture column through the broad area of low pressure and tropical wave. The latest satellite imagery shows scattered moderate to isolated strong convection between 60 and 120 nm of the low in the northwest quadrant. Scattered moderate convection is within 60 nm west of the wave along the monsoon trough from 09N to 11N. Both the TPW imagery loop and the latest METEOSAT imagery confirm the presence of very dry and stable air in the Saharan Air Layer north of 15N and east of 50W. The low pressure may develop some over the next 48 hours as it continues to the west. A western Caribbean tropical wave has its axis extending from near 18N79.5W to 13N80W, to central Panama at 09N80W and southward to the eastern Pacific near 07N80W. The wave has moved 20 kt during the past 24 hours, but appears to have slowed down some this afternoon and evening to an estimated speed of about 16 kt. Latest visible satellite imagery shows a broad field of low clouds moving in northeast to southwest fashion within 180 nm either side of the wave axis. Deep moisture and convection is being enhanced along and near the wave south of 16N due to the nearby proximity of an upper level low situated at 11N81W. The observed convection is seen in clusters of the scattered moderate type intensity from 13N to 15N between 78W-83W and within 60 nm of the axis from 10N-13N. This wave will move across the western Caribbean through early Monday afternoon before moving inland central America late Monday afternoon or evening. The earlier far western Caribbean tropical wave has moved inland central America and the Yucatan Peninsula to along 90W. It extends southward to the eastern Pacific to near 07N90W, and is moving westward near 15 kt. The combination of daytime heating and energy from this wave has induced clusters of scattered moderate convection over much of the Yucatan Peninsula, Belize and Honduras. ...ITCZ/MONSOON TROUGH... The Monsoon Trough axis extends from 14N17W to 11N25W to 10N32W to the 1011 mb tropical low at 10.5N46W and to just east of the tropical wave along 50W/51W. The ITCZ axis extends from just west of the same wave to 07N58W. Aside from the convection related to both Atlantic tropical waves and the tropical low as discussed above, scattered moderate to strong convection is seen within ' 120 nm north and 60 nm south of the monsoon trough axis between 35W-39W. Scattered moderate isolated strong convection is within 120 nm north of the ITCZ axis between 52W-56W and within 60 nm north of the same axis between 56W-58W. Scattered moderate isolated strong convection is south of the monsoon trough from 03N to 08N between 40W-45W. ...DISCUSSION... GULF OF MEXICO... An upper level low moving westward is over the far SW Gulf near 21N96W, with a cyclonic shear axis extending from the low northeast to 25N90W and to just south of the base of an upper trough near 29N84W. Upper level northeast flow is present to the northwest of the shear axis and low. A small upper level low is noted over S Florida. At the surface, a trough is analyzed over the far NW Gulf from just south of southwestern Louisiana to just northeast of Brownsville. The analysis revealed a very weak pressure gradient over the area that supports generally light to gentle winds throughout. Latest mosaic NW Doppler radar display along with satellite imagery shows scattered showers and isolated thunderstorms east of 91W, and also north of 25N west of 91W. The majority of this activity is waning. Scattered showers and thunderstorms are just offshore NW Cuba and the northern Yucatan Peninsula. Conditions across most of the Gulf are expected to remain very moist and unstable through early next week. A surface trough is approaching S Florida and the Straits of Florida. Expect showers and thunderstorms to remain quite active over the Straits and far southeastern Gulf into Monday. CARIBBEAN SEA... A tropical wave is along a position from 18N79.5W to 13N80W. See the section above for a discussion on this feature. Aside from the convection related to the aforementioned tropical wave, scattered moderate convection is over the northwest portion of Jamaica, and being enhanced by a small upper level low noted on water vapor imagery near 19N80W. The low is forecast to move off to the northwest through early next week. A deep pool of moisture resides across much of the southwestern portion of the sea. Resultant convective activity is described above in relation to the tropical wave. The water vapor imagery shows very dry air aloft across the eastern portion of the sea. Only isolated showers moving from east to west in low cloud lines are noted there. A tropical wave with associated low pressure is forecast to move across the Lesser Antilles and into the eastern Caribbean Sea on Tuesday accompanied by increasing winds and seas. ...HISPANIOLA... Scattered moderate to strong convection is presently over much of Haiti and the central and western section of the Dominican Republic. This activity will gradually weaken tonight. The presence of a very moist air mass in place along with the typical local island effects with daytime heating will allow for more of the same type of activity to develop on Monday afternoon and last into the evening hours. ATLANTIC OCEAN... Tropical waves are identified over the far eastern and central Atlantic. See the section above for discussions on these features. A large upper level low lifting northward is located on water vapor imagery to be near 30N70W, with a trough stretching southwestward to 26N70W to the southeastern Bahamas and to the eastern tip of Cuba. Another large upper level low gradually moving westward is over the north-central portion of the area at 29N49W, with a trough extending southwestward to 19N54W and southward to an elongated upper low at 15N55W. A small upper low is over the waters between the central Bahamas and central Cuba. Broad upper troughing is just northwest of the discussion area approaching the eastern United States. At the surface, a 1029 mb high is analyzed at 35W36W moving westward at 15 kt. A ridge extends from the high west-southwestward to 32N60W and to just east of NE Florida. A surface trough associated with an upper low over S Florida is along a position from 27N79W to just north of central Cuba as of 21Z. The atmosphere remains very moist and unstable over much of the area west of 61W, where scattered showers and isolated thunderstorms are evident. Scattered showers and thunderstorms are along the coast of Hispaniola west of 70W, and along the southern portion of the surface trough. These conditions are expected to change little through Tuesday. E of 70W, the atmosphere becomes very stable, except near the tropical waves and tropical low as described above. The METEOSAT-9 imagery shows an abundance of the Saharan Air Layer and associated dust spreading westward over much of the eastern and central Atlantic waters north of the tropical zone. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre