Complex sentence: Amid low shear and warm ocean temperatures, Gaston attained hurricane intensity for a second time by 18:00 UTC on August 27 and further intensified to become a Category 3 hurricane, the first major hurricane of the season, by 18:00 UTC the next day.
Split into simpler sentences: Amid low shear and warm ocean temperatures, Gaston attained hurricane intensity for a second time at 18:00 UTC on August 27. About 24 hours later, the storm deepened to a Category 3 hurricane, the first major hurricane of the season, by 18:00 UTC the next day.