"She will give her vision for the next 12 months, and the achievements of the last 12 months."
More announcements about Government help with Rātana housing are expected.
The opposition parties arrive at about 1pm and Waikato's Kingitanga contingent arrives at 3pm.
On Friday there's a big service in the Rātana temple, followed by a hakari (feast) for dignitaries. Across the event there will also be entertainment on the big marae stage and a youth (rangatahi) stage.
Big name entertainers include Luke Whaanga and the women's reggae group NRG Rising.
Young people will be playing volleyball, basketball and touch on Wednesday and Thursday, Meihana said, as well as livestreaming the event and having wānanga (workshops).
On November 8 last year the pā hosted a huge celebration marking the 100 years since Rātana was visited by the Holy Spirit, the event that began the movement. Thousands attended.
Because of that this year's birthday celebration could be smaller than usual - but at least 5000 people are expected.