WASHINGTON — The International Monetary Fund on Thursday trimmed its forecast for global economic growth for this year to take into account the impact of recent weakness in the US. But the global financial institution said growth prospects for next year remain undimmed, despite Greece's debt crisis and recent volatility in Chinese financial markets. In an update to its World Economic Outlook report, the IMF said the global economy should expand 3.3 percent this year, 0.2 percentage point below what it predicted in April. Growth should speed up to 3.8 percent next year, it said, unchanged from earlier forecasts. The IMF pinned much of the blame for the lower growth forecast on the United States. The US economy contracted in the first quarter, hurt by unusually heavy snowfalls, a resurgent dollar and disruptions at West Coast ports. The IMF said it expected the US economy to grow 2.5 percent this year – it lowered the US growth forecast last month from 3.1 percent in April. – Reuters