Mornings are best. The window from 7 to 10 a.m. is the best snorkeling of the day, every day, at every spot on Maui. Trade winds arrive late morning and build through the afternoon, adding choppiness that reduces visibility and makes conditions more difficult to navigate. By noon at most west side spots, it starts to get choppy. By 2 p.m. it's often not worth it. Plan to be in the water early and out by midmorning.
Skip the north shore during winter. From December through March, north shore spots like Honolua Bay and Kapalua get rough. In winter, snorkel on the south shore in places like Turtle Town, Wailea and Kīhei. Molokini tours run year-round but check sea conditions before booking — the crossing can be rough in winter. North shore snorkel spots are the best from May through September.
Check the surf report before you drive. NOAA's Maui surf report is a good source to check. Visit the site on the morning of your visit, not the night before. A 2- to 3-foot north swell means Honolua is too rough. A calm south swell morning means Turtle Town will be great. Don't commit to a spot until you've checked first.
Wait 24 to 48 hours after a heavy rain. Stormwater runoff carries bacteria and cuts visibility to near-zero at shore snorkel spots, especially on the north and west sides where stream runoff reaches the reef. Depending on the severity of the storm, water can remain murky well past 48 hours. Skip shore snorkeling after heavy rain and check conditions before returning.
Whale season changes the boat trip experience. December through April, humpback whales congregate in the Maui channel in significant numbers. Molokini boat tours during this period frequently encounter whales during the crossing or at the surface near the crater — this is a bonus that doesn't exist in summer. If you want to see whales, a winter Molokini tour offers a greater chance of spotting one.