Upvote:2
With climate being as changeable as it has been recently it seems that almost anything likely in one season may be possible in another, however the best indication I could find is that December is not a good choice for hammerhead shark spotting in Lombok. Mainly based on:
the best site being 'The Magnet' where schools of hammerheads frequent from the end of June until the first week of November
from Divescover.