Based on reports from Hurricane Hunters , the National Hurricane Center upgraded the depression to Tropical Storm Erin at 1530 UTC on August 13 about 250 miles ( 400 km ) east of Brownsville , Texas . Based on reports from Hurricane Hunters , the National Hurricane Center upgraded the depression to Tropical Storm Erin at 1530 UTC on August 15 about 250 miles ( 400 km ) east of Brownsville , Texas .