KEY WEST, Fla. (AP) — Forecasters say a strengthened Tropical Storm Isaac is bearing down on the Florida Keys. The U.S. National Hurricane Center in Miami said Isaac was centered about 135 miles (220 kms) east-southeast of Key West at 8 a.m. EDT Sunday. The storm has top sustained winds of about 65 mph (100 kph) and is moving toward the west-northwest at 20 mph (31 kph). Hours earlier, Isaac's winds were clocked at about 60 mph (95 kph). Forecasters say further strengthening is forecast over the next 48 hours with Isaac at or near hurricane strength when it reaches the Florida Keys later Sunday. The center says the storm could eventually become an extremely dangerous category 2 hurricane in coming days while taking aim at the northern rim of the Gulf of Mexico.