The two asteroids are due to make their close approaches past Earth on Friday, July 29th, and Saturday, July 30th, respectively.
The first of the two asteroids is named 2016 CZ31 and will make its close approach at 23:02 UTC on Friday, missing the planet by about 1,740,000 miles (2,800,000 kilometers). The asteroid orbits within the solar system and makes its closest pass by Earth every few years, with the next one due in January 2028. 2016 CZ31 measures roughly 400 feet (122 meters) across, with a width comparable to the height of a 40-story skyscraper.
The second asteroid, 2013 CU83, will make its close approach to Earth at 23:37 UTC. 2013 CU83 won't come as close to Earth, only coming as close as 4,320,000 miles (6,960,000 km) from Earth. This distance is 18 times the average distance between the Earth and the Moon, compared to 7 times that distance for 2016 CZ31's close approach. However, 2013 CU83 is much larger, measuring roughly 600 feet (183 meters) across at its widest point.
Though they are rather far away, NASA closely monitors near-Earth asteroids such as these. Small changes in their trajectory could result in a potential collision course with Earth on future approaches. You can track 2016 CZ31 here, and 2013 CU83 here.