730 AXNT20 KNHC 131751 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 151 PM EDT Fri Jul 13 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. ...SPECIAL FEATURES... ...Gale Warning off the coast of Colombia in the Caribbean Sea... The most recent scatterometer data provided observations of minimal gale force NE-E winds across the south-central Caribbean, particularly from 11N to 13N between 73W and 77W. In this area, sea heights range from 11 to 15 feet based on an altimeter pass. Minimal gale conditions are expected near the coast of Colombia at night through Sun night. Please, see the High Seas Forecast, under the AWIPS/WMO headers HSFAT2/FZNT02 KNHC, for more details. ...TROPICAL WAVES... Three tropical waves are between the west coast of Africa and the Lesser Antilles. These waves were relocated this morning based on visible satellite imagery, GOES-16 RGB Geocolor imagery, and Model Diagnostics Guidance. A tropical wave is added to the 1200 UTC analysis/surface map along 16W/17W from 06N-13N. Scattered to numerous moderate to isolated strong convection is just behind the wave's axis from 10N-13N between 14W-17W. The Hovmoller Diagram clearly shows the westward propagation of the wave. Model Diagnostics Guidance also confirms the presence of this feature. A tropical wave is along 41W from 08N-20N. Scattered moderate convection is behind the wave's axis and covers the area from 07N to 13N between 34W and 41W. A recent scatterometer pass indicates the wind shift associated with the wave's axis. African dust surrounds the wave. A tropical wave is along 59W from 07N-19N. Scattered moderate convection is noted near the base of the wave from 08N-12N between 58W-63W. This convective activity is affecting the islands of Trinidad and Tobago as well as NE Venezuela. Light showers or vicinity showers have been reported in Barbados, Trinidad and Tobago. A good surge of moisture is related to the wave based on the TPW product. Visible satellite imagery indicates some inverted-V pattern in the cloud field associated with this system. This wave will cross the Lesser Antilles through this evening, and move across the eastern Caribbean tonight through Sun. A tropical wave is along 70W from 09N-19N. This wave continue to enhance some shower activity over western Venezuela. The TPW animation indicates a modest surge of moisture associated with this wave. However, the GFS computer model suggests an increase in moisture in association with this wave as it moves across the central Caribbean through Sat night, then across the western Caribbean Sun and Sun night. A tropical wave has its axis over SE Mexico and western Guatemala and extends southward into the EPAC region. Currently, scattered showers are near the wave's axis. This system will move across the Tehuantepec area this afternoon and evening. ...MONSOON TROUGH/ITCZ... The monsoon trough passes through the coastal sections of Senegal near 14N17W to 11N30. The ITCZ extends from 11N30W to 12N40W to 07N50W to 09N58W. Aside from the convection related to the tropical waves, scattered moderate convection is from 05N-09N between 45W-53W. ...DISCUSSION... GULF OF MEXICO... A ridge continues to dominate the Gulf waters, with two weak high pressure centers of 1021 mb located across the northern Gulf. Under the influence of this system, mainly light to gentle anticyclonic flow will prevail across much of the Gulf region this upcoming weekend, with seas generally under 5 ft. Gentle to moderate SE-S winds are expected across the western Gulf on the western periphery on the ridge. According to the GOES-16 RGB Geocolor imagery, African dust has reached the SE Gulf, including the Yucatan Channel. A surface trough will move westward off the Yucatan Peninsula each evening through Tue. It will enhance nocturnal winds and seas over the SW Gulf. Marine guidance suggests fresh to locally strong NE-E winds and seas of 4-5 ft in association with this thermal trough. A tropical wave will move westward across the Bay of Campeche and the Tehuantepec region today. CARIBBEAN SEA... Two tropical waves will continue to move across the basin. Refer to the Tropical Waves section above for details. A gale warning is in effect for the south-central Caribbean. Refer to the Special Features section above for more information. Saharan dust covers most of the Caribbean Sea, including the Greater Antilles, where partly cloudy and hazy conditions prevail. High pressure will build across the region behind each passing tropical wave to freshen trade winds across the central Caribbean waters. Winds will pulse to strong to near gale force each night off the coast of Colombia through Tue, except to minimal gale force tonight, Sat night and Sun night. ATLANTIC OCEAN... An area of low pressure, associated with the remnants of Beryl, is located about 250 miles west-northwest of Bermuda. Although upper-level winds are at best marginally conducive, this system has become a little better organized today, and some additional subtropical or tropical development is possible tonight and Saturday while the low moves north-northeastward at about 10 mph. By Sunday, the system should reach colder water north of the Gulf Stream, where additional development is unlikely. The latest Tropical Weather Outlook gives this system a low chance of tropical cyclone formation during the next 48 hours. A weak low of 1014 mb is analyzed on the 1200 UTC surface map near 33.2 69.6W. Visible satellite imagery reveals that the low level center is totally exposed due to the strong winds aloft. A surface trough extends from the aforementioned weak low to the NW Bahamas. The trough will move little through Sun night while weakening. Scattered showers and isolated thunderstorms can be expected along and southeast of the trough. A recent scatterometer pass clearly indicates the wind shift associated with this trough. The remainder of the Atlantic forecast area is under the influence of the Bermuda-Azores High, with a center of 1034 mb located WNW of the Azores near 39N38W. The ridge extends SW into the NE Caribbean and the SE Bahamas. High pressure building westward from the central Atlantic through Tue will support fresh to strong trade winds south of 23N W of 65W. Winds will pulse to strong north of Hispaniola at night this weekend. The Saharan Air Layer (SAL) from CIMSS, and GOES-16 RGB Geocolor imagery, depict a large area of African dust covering the tropical Atlantic waters between the west coast of Africa and the Lesser Antilles. For additional information please visit http://www.hurricanes.gov/marine $$ GR