 At 10 : 00 a.m. , Coast Guard stations and United States Department of Agriculture ( USDA ) Weather Bureau offices at Lake Superior ports raised white pennants above square red flags with black centers , indicating a storm warning with northwesterly winds . By late afternoon , the storm signal flags were replaced with a vertical sequence of red , white , and red lanterns , indicating that a hurricane with winds over 74 mph ( 119 km / h ) was coming . The winds on Lake Superior had already reached 50 mph ( 80 km / h ) , and an accompanying blizzard was moving toward Lake Huron . 
