Kailua hava durumu: ay ay

March in Kona is the tail of whale season — humpbacks run from about mid-December to late March, thinning as the month goes on, so mid-March is still reliable and the very end of it is not. On rain, the forum's line that March is one of the Big Island's wettest months is about the windward side: on Kona's leeward coast March is one of the drier months, ten rain-days against fourteen through the summer. The variable that is genuinely local is vog — volcanic haze concentrates in the Kailua-Kona area and can bring headaches and eye and lung irritation, more seriously for asthma. The regulars' fix is geographic: drive north a few beaches and it largely clears.

Kona forum regulars are consistent about September: it's hot and sticky, and the trade winds that usually cool the coast can break down for stretches, so there's less relief than you'd expect. It's still technically hurricane season, and while a direct hit is rare, the remnants of a passing system can bring heavy surf and a burst of heavy rain even on an otherwise sunny week. That said, several posters described near-perfect two-week stretches with no crowds and easy access to snorkeling spots - it's a gamble, but one that tends to pay off more often than not.