Piha is a town on the west coast of Auckland Centennial Park, and is certainly worth making the trip through the park to get to it. Intermediate and expert surfers, kitesurfers, and windsurfers come out here to experience the big waves and strong winds.
The size of the beach depends on the tide, and it consists of hard black sand that is a good surface but gets hot in summer. There is plenty of room to launch a kite at low tide, but from December to February it gets busy with visitors. The water reaches a maximum of about 20° C in summer and 12° C in winter.
September to November provides the best conditions here, with the wind blowing from the west very consistently and reaching speeds in excess of 30 knots. The summer here is very hot, with air temperatures over 30° C and light winds, so kiting isn't really popular then. Autumn has lighter winds at 10 to 15 knots, with winter a bit stronger at about 20 knots. The conditions in the water are best at low tide, with the summer months giving waves between one and 3 m high and the winter and spring swells bringing in waves that can exceed three or even 4 m.
This place is set up really well and reflects its popularity. There are lifeguards, and a shop where you can buy gear. There are restrooms and showers, as well as food outlets, and you can park close to the beach and of course camp if you wish.
Take care with the currents if the swell is big, though they shouldn't be a problem for most people. Watch out for the crowds during summer.