On September 4, after moving into more favorable conditions, Irma strengthened into a Category 4 hurricane. As it continued approaching the Leeward Islands, Irma underwent a second and more robust period of rapid intensification, becoming a Category 5 hurricane by 12:00 UTC on the following day, with winds of 175 mph (280 km/h). The extremely powerful hurricane continued to intensify, with maximum sustained winds peaking at 180 mph (285 km/h) near 18:00 UTC on September 5. Irma acquired annular characteristics around this time, with the storm exhibiting a large, symmetric CDO and an impressive satellite appearance. Irma continued to intensify while approaching the northern Leeward Islands. Almost eight hours later, around 05:45 UTC on September 6, Irma made landfall along the northern coast of Barbuda at peak intensity, with the storm's central minimum pressure having bottomed out at – this was the lowest in the Atlantic since Dean in 2007; the storm also made landfall with maximum sustained winds of 180 mph (285 km/h). Irma continued to maintain its peak intensity until 12:00 UTC on September 6 and made additional successive landfalls on that same day, at 11:15 UTC on Sint Maarten, and at 16:30 UTC on Virgin Gorda, in the British Virgin Islands, though the storm's central pressure had risen slightly prior to its third landfall.