WASHINGTON, June 15 (Reuters) - Southwest Airlines (LUV.N) said on Tuesday it canceled about 500 flights and delayed hundreds of others after it was forced to temporarily halt operations over a computer issue -- the second time in 24 hours it had been forced to stop flights. The Federal Aviation Administration said it had issued a temporary nationwide groundstop at the request of Southwest Airlines to resolve a computer reservation issue. The groundstop lasted about 45 minutes, and ended at 2:30 p.m. EDT (1830 GMT), it said. Southwest said its operations were returning to normal. The issue was the result of "intermittent performance issues with our network connectivity." Southwest delayed nearly 1,300 flights on Tuesday, or 37% of its flights, according to flight tracker FlightAware. Southwest Airlines earlier reported a separate issue that required a groundstop Monday evening after its "third-party weather data provider experienced intermittent performance issues ... preventing transmission of weather information that is required to safely operate our aircraft." The airline said that issue affected several hundred flights and was resolved after 11 p.m. CDT Monday.