Seven previous posts at this website have mentioned the potential interaction between pencils and humidity. The Staedtler 190T and Tajima carpenter’s pencil have specifically claimed to address certain humidity concerns.
With help from the Wayback Machine, we have some specifics courtesy of a brief article in the 2003 Pentel Library. (The page loads slowly.) Pentel suggests that a 2B lead in humid Okinawa performs like an HB lead elsewhere! The idea is that paper becomes softer in high humidity, with the lead adhering less to the paper. A 2B lead in humidity is thus needed to make a mark similar to an HB mark in an arid environment.