The U.S. National Hurricane Center says Tropical Storm Irene is strengthening as it approaches Puerto Rico with winds of 110 kilometers per hour, nearing hurricane strength. Forecasters say hurricane conditions are expected in Puerto Rico within hours. The Dominican Republic is also under a hurricane warning with the high winds, severe rain and high tides expected on Monday. A hurricane watch is in effect for the U.S. Virgin Islands and the central Bahamas. Tropical storm conditions are expected in much of the rest of the region.