000 AXNT20 KNHC 160005 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 805 PM EDT Sat Jul 15 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 extending from 14N44W to 04N45W, moving westward at 10-15 knots. The wave has dry Saharan air well to the west of its axis as depicted in the latest METEOSAT-9 Saharan Air Layer imagery as well to its east. Scattered moderate isolated strong convection is within 180 nm east and 120 nm west of the wave from 09N to 10N. This wave may possibly acquire more convection early next week with the possibility of low pressure forming along it. A central Caribbean tropical wave has its axis extending from 19N69W to inland northwestern Venezuela at 12N72W, moving westward near 20 kt. Streamline analysis from the GFS model depicts 700 mb troughing over the general location of this wave. Scattered moderate to strong convection is inland the coast of Venezuela from 09N to 12N between 69W-71W. Scattered moderate convection is east of the wave axis from 13N to 17N between 68W-70W. Scattered showers and isolated thunderstorms are ahead of the wave to 75W from 14N to 17N. Some of this activity may contain gusty winds. The wave is forecast to move across the rest of the central Caribbean through Sunday afternoon, and across the western Caribbean Sunday evening through Monday. A western Caribbean tropical wave has its axis extending from just south of western Cuba near 21.5N82W to 15N83W to inland northern Costa Rica, moving westward at 15-20 knots. The northern portion of the wave's axis is lies to the east of a small upper level low that is located between northwestern Cuba and the Yucatan Peninsula. A cyclonic shear axis is evident extending from the low to another small upper low over Jamaica. Deep moisture along with ample instability present over the far northern Caribbean to the north of 19N and west of Jamaica including the environment over the northern portion of the wave is combining to bring developing scattered showers and thunderstorms north of 19N between 79W-82W. Very deep moisture over the far SW Caribbean, some associated with the close proximity of the eastern Pacific monsoon trough, is combining with instability provided by the wave to produce scattered showers and thunderstorms south of 14N west of 79W. Isolated showers and thunderstorms are elsewhere within 240 nm west and 180 nm east of the wave axis. This wave will move across the remainder of the western Caribbean through Sunday afternoon and inland the Yucatan Peninsula and central America Sunday evening. ...ITCZ/MONSOON TROUGH... The Monsoon Trough axis extends from 12N17W to 09N30W to just east of the tropical wave along the position from 14N46W to 04N48W. It resumes just west of the same wave to just northeast of the coast of South America near 06N54W. Aside from the convection related to the tropical wave along 47W, scattered moderate isolated strong convection is within 120 nm north of the axis between 35W-40W. Scattered moderate convection is within 240 nm south of the axis between 40W-46W, within 180 nm north of the axis between 40W-43W, and within 60 nm south of the axis between 22W-29W. Scattered moderate to isolated strong convection is noted south of the monsoon trough from 03N to 08N between 31W-39W. ...DISCUSSION... GULF OF MEXICO... A small upper level low is over the far northeast portion of the Gulf at 29N85W, with a trough stretching southwestward from it to another small upper level low over the far southwestern Gulf at 21N94W, moving westward. At the surface, a persistent surface trough is analyzed over the central Gulf along a position from 29N88W to 22N89W, drifting westward. With these features in place, abundant deep moisture and plenty of instability remain in place over just about the entire basin, except for the far southeastern portion where dry air aloft is advecting west-southwestward south of 27N and east of 85W as seen in water vapor imagery. Latest national mosaic radar display and satellite imagery show scattered showers and thunderstorms north of 26N east of 92W. Isolated showers and thunderstorms are noted elsewhere across the Gulf. Scattered moderate to isolated strong convection is over much of the northern and western sections of the Yucatan Peninsula due to the daily thermal trough that becomes established there during the afternoons. A rather weak pressure pattern is analyzed over the area. The present moisture along with the induced shower and thunderstorm activity will change little through at least Sunday night. The western periphery of Atlantic high pressure is forecast to protrude more westward across the eastern and central Gulf later on Monday and into Tuesday. CARIBBEAN SEA... A couple of tropical waves are moving through the Caribbean Sea. See the section above for details. Aside from the convection related to these waves, isolated showers and thunderstorms are noted elsewhere over much of the sea. A relatively light pressure gradient over the area is allowing for generally light to moderate trades to exist across the sea, except for fresh to locally trades over the south-central portion of the sea. Little change is expected with these conditions into Monday. Moisture and resultant convection is expected to be on the increase over the western half of the sea and portions of central America through Monday. ...HISPANIOLA... Scattered moderate convection is occurring over much of the interior portions of island early this evening as a result of earlier afternoon heating and sea breeze. The northern portion of a central Caribbean tropical wave is passing through the south- central part of the island. Scattered showers and thunderstorms are seen east and southeast of the wave. It is possible that some of this activity will affect portions of the island through Sunday as the wave advances westward. ATLANTIC OCEAN... A tropical wave is moving across the central Atlantic. See the section above for details. A large upper level low lifting northward is centered near 29N69W. A resultant surface trough is along a position from near 32N65W to 22N66W. Scattered showers and thunderstorms are seen north of 25N between 60W-65W, while scattered showers and isolated thunderstorms are north of 26N between 65W-73W. An upper trough extends from the low southwestward to between Hispaniola and Cuba and to an upper level low over Jamaica. Another upper level low moving westward is over the eastern Atlantic near 28N45W, with a trough extending south-southwestward to near 16N49W and to near 10N52W. Elsewhere at the surface, a trough is over the central Bahamas along a position from near 26N76W to inland central Cuba at 22N78W. This trough is being supported by an upper level trough that extends from the upper level low near 29N69W to the near the southeastern and central Bahamas. Plenty of moisture and instability over waters south of 26N between 74W and 79W is inducing increasing scattered showers and thunderstorms over those same waters including the Bahamas and just about the entire island of Cuba. The surface trough is forecast to slowly move westward through the remainder of the Bahamas through Sunday, and reach southern Florida Sunday night. The associated moisture along with the shower and thunderstorm activity will translate westward with this trough. Otherwise, the remainder of the basin is under the influence of a surface ridge, anchored by a 1026 mb high centered near 33N52W. Abundant Saharan air and associated dust covers just about the entire eastern Atlantic, and much of the central Atlantic areas per latest METEOSAT-9 imagery. The dust is gradually migrating westward as some has already entered the far eastern Caribbean Sea. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre