Katrina again began to quickly strengthen , reaching Category 5 strength on the morning of August 28 and reached its strongest point with maximum sustained winds of 175 mph ( 280 km\/h ) and a minimum central pressure of 902 mbar . Katrina again rapidly intensified , attaining Category 5 status on the morning of August 28 and reached its peak strength at 1:00 p.m. CDT that day , with maximum sustained winds of 175 mph ( 280 km\/h ) and a minimum central pressure of 902 mbar .