With sun and perfect fall temperatures predicted, nearly 4,000 Success Academy Queens parents and supporters are expected to show at Roy Wilkins Park in St. Albans for Thursday’s rally demanding Department of Education action on the network’s request for space for a new middle school.

The DOE is already over a year late in delivering: Success’ existing Queens middle school had to squeeze students in tight this year, eliminating art and science rooms.

Because the process for fully OK’ing space is so drawn-out, if the bureaucrats don’t identify a specific public school for the new school soon, it won’t be able to open in time — and the parents of more than 200 mostly minority and low-income Queens kids who’ve prospered at Success elementary schools will have to make other arrangements.

At least seven public school buildings in the borough have 450 or more empty seats — plenty of room for the new Success school. But the DOE stays silent.

The obvious reason for the holdup: Mayor Bill de Blasio and Chancellor Richard Carranza’s open hostility to charters, especially Success. No matter that existing Success schools are already some of the very best public schools in Queens.

These parents have plenty to be angry about: Expect to hear them roar.