WASHINGTON (MarketWatch) - The average wage of American workers rose 0.3% in May to $24.96 a hour, pushing the increase over the past year up to its highest level since mid-2013. The increase last month means wages in the past 12 months have risen at a 2.3% rate for the first time since August 2013 and only the third time since 2010. Year-over-year increases had stuck to a tight range of 1.9% to 2.2% since 2012 even though the labor market has tightened considerably in the past few years. Most economists expect hourly wages to rise to 2.5% annual rate or higher as the dwindling pool of workers forces companies to pay more. That would give the U.S. economy an added boost. The amount of time people worked each week, meanwhile, was flat at 34.5 hours, just a notch below a post-recession high.