Hawaii beaches become the busiest ones in winter (December - February), mainly because of the weather elsewhere. The period from June till October is the hottest beach weather, from December till March - the wettest. The average temperatures are more or less the same in winter and in summer. Hotel prices are the highest from mid-December till the end of March.
If you're into surfing, winter months are the best, especially the Christmas season at Oahu's North Shore, otherwise summer (July-August) has the best water condition for swimming, snorkeling, windsurfing and scuba diving.
The best beach resort for swimming, snorkeling, scuba diving in Hawaii is Hanauma Bay Nature Preserve, Oahu, situated in the crater of a volcano, one of the Hawaiian's most beautiful bays, with world-class snorkeling and scuba diving. It is a conservation area, so it has strict rules, such as no smoking (the first no-smoking beach in USA), no consumption, and only 2000 visitor per day, so go early in the busy season.
Whether you're a novice or an experienced diver...you'll enjoy a rare and unforgettable oceanic tour exploring the best of the Hawaiian underwater with Maui Sealife Scuba School. Don't miss an opportunity to appreciate Maui's unique underwater wonderland while learning the relaxing sport of scuba diving. Capture an intimate glimpse of amazing seascapes - colorful shallow waters, living reefs, delicate hills, vivid marine life and magical sea caves.
It can get crowded, but for clear, warm, calm waters, an abundance of fish that are so friendly they'll swim right up to your face mask, a beautiful setting, and easy access, there's no place like Hanauma Bay. Just wade in waist-deep and look down to see more than 50 species of reef and inshore fish. Snorkelers hug the safe, shallow inner bay - it's like swimming in an outdoor aquarium. Serious divers shoot "the slot," a passage through the reef, to enter Witch's Brew, a turbulent cove.
Another popular spot in Hawaii more than suitable for swimming, snorkelling, body surfing, surfing, kayaking, scuba diving is Kaanapali Beach, Maui. Kaanapali beach is located in front of the Kaanapali Resort, extending nearly 3 miles from Kahekili Beach in the north to Hanakaoo Beach (Canoe Beach) in the south. The beach is lined by hotels, restaurants and activity centers and is one of the best place for watersports and activities in Hawaii. During no or low surf seasons, snorkeling and scuba diving are fantastic around Black Rock (a volcanic cinder cone on the north end of the Kaanapali Beach, known as Airport Beach). Surfing is good to the south near the Marriot Hotel. Kaanapali has outstanding views across the Auau Channel and was voted 'Beach with the Best Sunset' by the Hawaii Magazine 1999. The beach can be overcrowded and thefts occur.
The calm, shallow waters of Kahaluu are perfect for beginning snorkelers or those who are unsure of their swimming abilities and want the comfort of being able to stand up at any time. The sunlight through the shallow waters casts a dazzling spotlight on the colorful sea life and coral formations. If you listen closely, you can actually hear the parrotfish feeding.