Simplify the following text for a Grade 6 native English-speaking person.
Original: The first storm of the season , Allison lasted unusually long for a June storm , remaining tropical or subtropical for 15 days . The storm developed from a tropical wave in the northern Gulf of Mexico on June 4 , 2001 , and struck the upper Texas coast shortly thereafter .
Simplified: The wave moved north until June 4 , where it became Tropical Storm Allison .