Simplify the following text for a Grade 7 native English-speaking person.
Original: Moisture from the system produced heavy rainfall over the island of Hawaii , totaling to over 15 inches . The flooding closed all major roads in Hilo , and was considered the worst flooding in 40 years .
Simplified: Moisture from the system produced heavy rainfall over the island of Hawaii , totaling to over 15 i. The flooding closed all major roads in Hilo , and was considered the worst flooding in 40 years .