493 AXNT20 KNHC 201741 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 141 PM EDT Thu Sep 20 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 1200 UTC surface analysis and satellite imagery through 1715 UTC. ...TROPICAL WAVES... An eastern Atlantic tropical wave is located along 25W from 05N- 20N moving west at 10 to 15 kt. The total precipitable water (TPW) satellite animation shows a well-depicted plume of moisture trailing the wave between 22W and the coast of Africa. Scattered showers are near the wave axis south of 12N. A central Caribbean tropical wave has its axis along 70W extending from the Dominican Republic to western Venezuela moving west around 15 kt. TPW imagery shows enhanced moisture associated with this tropical wave. Scattered moderate convection is noted from 15N-19N between 67W-72W. This activity is currently affecting the southern coast of the Dominican Republic. Satellite imagery indicates some Saharan dust east of the wave from 12N-24N between 57W-67W. Puerto Rico and the Virgin Islands are reporting hazy conditions. Strong wind gusts are possible near showers and storms associated with this wave through Friday as it moves westward through the central Caribbean. The wave is expected to increase the likelihood of showers and thunderstorms over the remainder of Hispaniola today, and across eastern Cuba and Jamaica on Friday. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from coastal sections of Sierra Leone near 08N13W to 07N16W to 09N23W. The ITCZ begins near 09N26W and extends to 07N35W to 09N46W, then resumes from 09N52W to the Guyana/Venezuela border. Scattered moderate and isolated strong convection is seen within 270 nm south of the trough axis between 21W and the coast of Africa. Scattered moderate convection is noted with the ITCZ from 07N-10N between 50W and the coast of South America. ...DISCUSSION... GULF OF MEXICO... Water vapor imagery and model analyses indicate the presence of an upper-level cyclonic shear axis stretching from the Florida Straits to southeast Louisiana. At the surface, a trough extends from near Ft. Myers, FL southwestward to near 24N86W. Another trough extends through the central Bay of Campeche from 24N91W to the coast of Mexico near 18N93W. Isolated showers and thunderstorms are noted over the Bay of Campeche. This trough and associated moisture will move westward, reaching mainland Mexico by late Fri. A small 1019 mb surface high is centered over northern Florida near 30N83W. Ridging will build in across the northern Gulf, producing gentle to moderate east to southeast winds and 2 to 4 ft seas across the basin through Sun. CARIBBEAN SEA... A tropical wave is moving across the east-central Caribbean Sea. See the Tropical Waves section for more details. A 1008 mb low along the monsoon trough is located in the southwest Caribbean near 11N82W. These features are producing numerous moderate to strong convection over the southwest Caribbean from 10N-13N between 77W-86W. This activity is affecting parts of northern Costa Rica and Nicaragua, including the city of Bluefields, where heavy thunderstorms are currently being reported. Plenty of moisture will persist over the southwest Caribbean through Saturday as the tropical wave, currently along 70W, reaches the area and moves inland into central America late Sat or early Sun. Recent scatterometer data show fresh to occasionally strong trade winds south of 18N, between 70W-83W, while an altimeter pass indicates seas as high as 11 ft near the coast of Colombia. Over the eastern Caribbean, winds are in the 15-20 kt range with seas near 8 ft. High pressure building from the central Atlantic into the central Bahamas will continue to support similar winds and seas, especially over the south-central Caribbean, through Friday night. Scattered showers and thunderstorms embedded in the trade wind flow are moving across Trinidad and Tobago into far NE Venezuela. ATLANTIC OCEAN... A 1012 mb surface low, formerly a tropical wave, is producing a concentrated area of thunderstorms near 10.5N49W, or about 740 nm east of the Windward Islands. Although this disturbance shows some signs of organization on satellite imagery, there is no evidence of a surface circulation at this time. A recent ASCAT pass confirms the presence of an open trough. Scattered moderate convection in a banding pattern is noted from 10N-13N between 46W- 50W. Some additional development is possible today before upper- level winds become highly unfavorable for tropical cyclone formation starting tonight and continuing through the weekend. The remnant of Joyce is analyzed as a 1014 mb low near 30N32W. A trough extends from the low to 26N34W. No significant convection is noted. A cold front enters the forecast area near 31N69W and continues southwestward to 29N73W to 29N79W. Scattered showers are within 120 nm ahead of the frontal boundary between 70W-78W. East of the front, a surface trough is analyzed from 29N62W to 23N70W. Scattered showers and thunderstorms are located within 150 nm east of the trough. Scatterometer data indicate winds of 20-25 kt are currently occurring north of 29N between 64W-69W. This area of 20-25 kt winds will move eastward over the area for the next 12 hours before gradually weakening. The aforementioned front will sink SE to the waters north of 27N through Fri before the front dissipates. A relatively weak pressure gradient prevails over the remainder of the Atlantic area. For additional information please visit http://www.hurricanes.gov/marine $$ HAGEN/GR