Simplify the following text for a Grade 10 native English-speaking person.
Original: When Tropical Depression Thirteen strengthened into Tropical Storm Luis on August 29 , it marked the earliest date that a seasons ' twelfth named storm formed , surpassing the previous record set on August 31 , 1933 when Tropical Storm Twelve formed near the Lesser Antilles . Luis spent a week as a major hurricane .
Simplified: When Tropical Depression Thirteen became Tropical Luis on August 29 , it marked the earliest date of a seasons 12th named storm .