Three massive school systems in Florida announced Tuesday they plan to close Thursday and Friday to allow people to prepare for Hurricane Irma.

School officials in Broward, Miami-Dade and Palm Beach counties said they would cancel classes as the storm barreled towards the United States. The three school districts together educate more than 820,000 students.

School officials made the decision to close as their counterparts in Texas continue to assess damage from Hurricane Harvey, which caused the worst natural disaster in the state’s recorded history. The Houston Independent School District, with 218,000 students, announced it would open Sept. 11, two weeks behind schedule.

The closures mean four of the nation’s 10 largest school districts will be shuttered because of hurricanes. The district rankings come from 2014 enrollment data reported by the National Center for Education Statistics.