sentence: While drifting across the region, upper-level winds calmed down enough for the tropical disturbance to strengthen and to develop into Tropical Depression Fifteen on October 13. It strengthened to Tropical Storm Omar the next day.
modified: While drifting across the region, upper-level winds calmed down enough for the tropical disturbance to strengthen and to develop into Tropical Depression Fifteen on October 13. It strengthened to Tropical Storm Omar the next day.