On Thursday, Marblehead School Committee member Richard Nohelty will resign from his post. Nohelty made the announcement official in a recent letter to the School Committee. His resignation marks the third departure from the panel this year. Former vice chairman Jonathan Lederman did not run for reelection, and chairwoman EuRim Chun resigned in June. Also, Greg Maass, citing a difference in philosophy with some members of the School Committee, resigned as school superintendent in June. His post has been filled by Maryann Perry. The School Committee and Board of Selectmen plan to hold a joint meeting to interview and appoint a new member to fill Nohelty’s position.