Original: On the night of August 27, Katrina underwent another episode of rapid deepening, strengthening to a Category 5 hurricane with maximum sustained winds of 175 mph (280 km\/h) by 10:00 am CDT on August 28.
Simplified: That night, the storm underwent another period of rapid strengthening, strengthening to a Category 5 hurricane with maximum sustained winds of 175 mph (280 km\/h) by 10:00 am CDT on August 28.