000 AXNT20 KNHC 211735 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 135 PM EDT Sun May 21 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 1200 UTC surface analysis and satellite imagery through 1715 UTC. ...TROPICAL WAVES... Visible satellite animation suggests that a new tropical wave is about to emerge off the coast of Africa. This wave will likely be added to the 1800 UTC analysis/surface map. A weak tropical wave is in the eastern Atlantic and extends from 12N31W to 04N32W, moving west at 10-15 kt. Based on current SAL analysis from UW-CIMSS, african dust surrounds the wave. As a result, only a few showers are noted near the wave axis. A tropical wave is moving across the eastern Caribbean. Its axis extends from 17N63W to NE Venezuela near 08N64W, moving west at around 15 kt. Convection is limited in association with this wave. The TPW animation shows a modest surge of moisture in the wake of the wave axis. ...ITCZ/MONSOON TROUGH... The Monsoon Trough enters the tropical Atlantic through Sierra Leone near 08N13W and continues to 07N21W. The ITCZ extends from 07N21W to 06.5N30W, then resumes west of a tropical wave at 06N35W to 05N45W to NE Suriname. Scattered moderate convection is noted within about 120 nm of the african coast between 03N- 14N. Scattered moderate to isolated strong convection is from 07N-09N between 16W-18W. ...DISCUSSION... GULF OF MEXICO... Mosaic Doppler Radar from the SE U.S. shows numerous showers with embedded tstms from SE Louisiana to the Florida Panhandle, including also the NE Gulf. A surface trough is analyzed on the 1200 UTC map within this area and goes from 31N82W to 28N86W. Scattered showers and tstms are also noted near the coast of Texas and the NW Gulf in association with a stationary front. This system is forecast to weaken near the northern Gulf coast in about 24-48 hours. Once again, areas of fog were observed over the NW Gulf under the influence of a moist and warm SE wind flow. High pressure of 1023 mb located over the western Atlantic near 31N72W extends a ridge across Florida into the Gulf of Mexico. The pressure gradient between the ridge and lower pressures across Mexico and the far west Gulf waters is generally maintaining moderate SE winds over the Gulf. Fresh winds were noted to the N of the Yucatan Peninsula due to the presence of the thermal trough. Gusty winds to near 30 kt are seen per buoy observations near the convective activity over the NE Gulf. The ridge is forecast to shift southward tonight through Tuesday as the weak frontal boundary remains along the Northern Gulf Coast while weakening. A stronger cold front will enter the NW Gulf by Tuesday night. CARIBBEAN SEA... Numerous moderate to isolated strong convection persists over the SW Caribbean, particularly south of 12N. This convective activity is associated with a northward displacement of the monsoon trough that currently crosses parts of Costa Rica and Panama to a 1008 mb low along the coast of Colombia near 11N76W. Upper-level diffluence is also helping to induce this convective activity, that is forecast to persist over the SW Caribbean and southern central America for the next several days. A tropical wave is moving across the eastern Caribbean. Please refer to the TROPICAL WAVE section above for details. High pressure located near 31N72W combined with the Colombian/Panamanian low is supporting fresh to strong trade winds over the central Caribbean. Similar wind speeds are also noted W of 85W, including the Gulf of Honduras. These winds are expected to diminish tonight and Monday as the ridge weakens in response to low pressure moving eastward from the Eastern United States. Patches of low level moisture, embedded in the trade wind flow, are observed elsewhere across the region. The Saharan Air Layer from UW-CIMSS and visible satellite imagery reveal the presence of african dust reaching the Lesser Antilles and the far east Caribbean. Some of the islands are currently reporting haze and dust. ...HISPANIOLA... Daytime heating, local sea breezes and mountain upslope lifting will combine with available shallow moisture to produce some cloudiness with scattered showers mainly during the afternoon and early evening hours today and Monday. A tropical wave, now moving across the eastern Caribbean, could enhance the shower activity on Monday. ...ATLANTIC OCEAN... High pressure prevails across most of the Atlantic Ocean. As previously mentioned, a 1023 mb high is located near 31N72W while another high pressure center of 1025 mb is near 28N35W. The latter one will move eastward to a position near 28N30W in about 24 hours. Moderate to fresh trades are seen per scatterometer data across the tropical Atlantic west of 35W. A surface trough, likely a reflection of an upper-level trough, extends from 28N56W to 21N62W. Scatterometer data combined with buoy observations continue to show the wind shift associated with this trough. Scattered moderate convection is within about 210 nm SE of the trough from 23N-27N. A low appears to be forming along the trough axis near 24N61W. This feature is ahead of an upper- level trough that extends from 31N54W to the Mona Passage. Upper diffluence ahead of the trough is helping to maintain the shower activity ahead of the surface trough. For additional information please visit http://www.hurricanes.gov/marine $$ GR