Wood was dominant in last year's championships in Dunedin, when he beat James Dinnis (Taranaki), but he can expect stiffer competition in this year's four-day event.
Wood won the title in 2008 before losing narrowly to Dinnis a year later.
Clayton Dougan (Wellington) was third last year but has improved his skills in the strong winds on the Wellington Harbour.
Each of the 45 competitors will have two races each day and the winner is the surfer who scores the most points. There is no final.
Crombie finished just ahead of Sue Bradley (Queenstown) last year to regain the title that Bradley took off her in 2009.
Nicola Taylor (Christchurch), third last year, could be the dark horse this week.
Veteran Tim Wood (Auckland), who raced professionally in England in the past, is expected to dominate the grand masters over age 55 grade.
In the youth under-25 grade, Dunedin's Dan Meehan will be the favourite to take the title on his home course at his first national championships.
This will be the fifth consecutive year that the championships have been held on the Otago Harbour.
The Oceanic championships is being held in conjunction with the event and has attracted top Australians Issac de Vries and Rowan Law.
The Oceanic championships is a formula 42 event that limits competitors to a choice of two boards and four sails.
The venue is known as one of the best slalom areas in New Zealand. During summer there is a strong sea breeze that funnels down Otago Harbour and provides perfect slalom conditions for up to five days a week.
The headquarters for the event is the Otago Windsurfing headquarters, at Kitchener Street. The championships conclude on Saturday.
