The three moons in the fall of the year would be called:
Re-Hollys Mooar yn Ouyr, the Harvest Moon to ripen corn;
Re-Hollys mooar my Cabbil, The Great Moonshine Horse, after which the horses would have to be housed at night; and
Re-Hollys mooar cooil y cleigh, The Great Moonshine that hove no shadow behind the hedge.
Whichever way the weather was on the first of these moons it would be expected to be the same for all three.
(source: Wm. Cashen’s Manx Folk-lore (1912); photo http://bit.ly/19gSDuW plus graphic)