155 AXNT20 KNHC 061739 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 139 PM EDT Mon Aug 6 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 1730 UTC. ...SPECIAL FEATURES... Gale warning over the south-central Caribbean... A strong ridge over the E CONUS extending E to Atlc adjacent waters W of 60W will tighten the pressure gradient in the south-central Caribbean. Wind gusts reaching gale-force are expected starting tonight, then sustained gale-force winds are forecast for the Gulf of Venezuela on Tue night and along the coast of Colombia by Wed night. Please see the National Hurricane Center Atlantic High Seas Forecast under AWIPS/WMO headers MIAHSFAT2/FZNT02 KNHC for further details. ...TROPICAL WAVES... A tropical wave is in the eastern Atlantic with axis extending from 07N-18N along 35W, moving W at 10 kt. This wave continues to be affected by Saharan dry air and dust intrusion, which is limiting convection to the area where the wave meets the ITCZ from 09N-12N and west of 35W. A tropical wave is in the central Atlantic with axis extending from 01N-14N along 48W, moving W at about 10-15 kt. The wave continues to be affected by intrusion of Saharan dry air and dust as indicated by GOES-16 RGBs, water vapor and CIRA LPW imagery at the lower levels. Shallow moisture in the vicinity of the ITCZ supports scattered moderate convection mainly S of 10N. A tropical wave is in the E Caribbean with axis S of 21N along 70W, moving W at 5-10 kt. The wave is in a very moist environment at the lower levels as indicated by CIRA LPW and GOES-16 water vapor imagery. The wave is underneath a diffluent environment between an elongated upper-level low over the central basin and S-SW flow to the E, which is supporting scattered showers N of 17N between 68W-72W. A tropical wave is in the W Caribbean with axis S of 21N along 80W, moving W at 10 kt. CIRA LPW imagery shows shallow moisture associated with the wave. Shallow moisture in the vicinity of the monsoon trough supports scattered moderate convection mainly S of 10N. ...MONSOON TROUGH/ITCZ... The monsoon trough enters the eastern Atlantic near 20N16W to 14N31W. The ITCZ begins W of a tropical wave near 10N38W and continues to 08N46W, then resumes near 07N51W to 09N61W. Aside from the convection related to the tropical waves, scattered moderate convection is observed along the ITCZ. ...DISCUSSION... GULF OF MEXICO... A broad area of high pressure extends from eastern CONUS across the basin. A surface trough extends across the northwest Gulf along 96W and north of 27N. Scattered moderate convection is observed with this trough mainly north of 25N and west of 94W. Another trough extends across the Bay of Campeche with scattered showers. Return flow provided by the surface ridge continues to advect shallow moisture from the Caribbean and into the Gulf, which is supporting scattered moderate convection across the Yucatan Channel and south-central Gulf waters between 84W-90W. A third surface trough is in the far east Gulf from the Florida Big Bend to 29N84W with no significant convection at this time. Expect for convection to continue across the west Gulf through tonight. Isolated showers are forecast in the Bay of Campeche through the middle of the week associated with a thermal surface trough that will come off the Yucatan Peninsula at night. This trough will also enhance the winds to fresh off the W Yucatan Peninsula. Surface ridging is forecast to prevail through the week. CARIBBEAN SEA... GOES-16 RGBs continue to show a thin layer of Saharan dust moving across most of the basin where strong deep-layer wind shear prevails. This environment continues to suppress the development of significant convection across the basin. However, shallow moisture is across the basin supporting scattered showers within 90 nm off the southwest of Cuba. To the south, the monsoon trough supports similar convection within 75 nm off Panama. A tropical wave is in the W Caribbean lacking convection, while an upper- level low over Hispaniola is supporting convection near the northern portion of the wave currently along 70W. See the Tropical Waves section above for further details. Fresh to near- gale force winds in the south-central Caribbean are forecast to increase to gale-force gusts in the Gulf of Venezuela and off the coast of Colombia by tonight, then sustained gale-force winds will develop through midweek. See the Special Features section for further details. ATLANTIC OCEAN... Two tropical waves are moving across the basin. Refer to the section above for details. A non-tropical, surface low pressure system centered near 31N50W is interacting with a broad upper- level low. Although the system is producing disorganized showers and thunderstorms to the east and northeast of the center, environmental conditions are expected to be only marginally conducive for the low to acquire subtropical or tropical characteristics while it moves north or north-northeastward over the next day or so. The low is forecast to move over cooler waters by Tuesday night, and development is not expected after that time. Southeast of this low, a surface trough extends from it to 26N57W supporting scattered showers and tstms N of 30N between 40W-50W. Aside from the tropical waves, the remainder of the Atlc is under the influence of surface high pressure that supports fair weather. For additional information please visit http://www.hurricanes.gov/marine $$ ERA