Interfinity by Bryan Davis

Interfinity is imminent. The merging of the three Earths means one thing to Nathan Shepherd — he must save all three worlds. He and his friend Kelly witness the results of the coming cosmic collision. Earth Yellow dwellers have dreams of future tragic events while the other two Earths experience Earth Yellow's weather changes at hyperspeed. Panic sets in, and only Nathan, Kelly, and their allies can prevent the looming disaster that threatens to kill billions.