How to fix a leak in the wall

I seem to have a leak in the wall. I don't think it's plumbing related because it just seems to appear during rainy days. Is there anything I can do before more damage occurs? Unfortunately it's going to be a rainy week here and these are crazy times given COVID-19 status. Many thanks in advance.

EDIT: More details: leak is on an East-facing 1st FL wall. No visible signs of leak on 2nd or 3rd floors. Asked neighbor, he denied any leaks. Wall is shared with another house (row-home style, adjacent house on east wall and west wall). Roof inspection two months ago didn't reveal any issues (purchased house a month ago). Roof pictures below, it looks like the leak location coincides with the neighbor's chimeny.