Hurricane Katrina formed as Tropical Depression Twelve over the southeastern Bahamas on August 23, 2005, as the result of the merger of a tropical wave and the remnants of Tropical Depression Ten four days earlier. The storm strengthened into Tropical Storm Katrina on the morning of August 24. The tropical storm moved towards Florida and became a hurricane only two hours before making landfall between Hallandale Beach and Aventura on the morning of August 25. The storm weakened over land, but it regained hurricane status about one hour after entering the Gulf of Mexico, and it continued strengthening over open waters. On August 27, the storm reached Category 3 intensity on the Saffir-Simpson hurricane wind scale, becoming the third major hurricane of the season. An eyewall replacement cycle disrupted the intensification but caused the storm to nearly double in size. Thereafter, Katrina rapidly intensified over the "unusually warm" waters of the Loop Current from a Category 3 hurricane to a Category 5 hurricane in just nine hours.