Simplify the following text for a Grade 8 native English-speaking person.
Original: The U.S. Government 's National Weather Service defines a gale as 34 to 47 knots ( 63 km\/h to 87 km\/h or 39 miles per hour to 54 miles per hour ) of sustained surface winds .
Simplified: The U.S. government 's National Weather Service defines a gale as 34 â `` 47 knots ( , or ) of sustained surface winds .