"I think today was possibly the last day of being really hot. Tomorrow is probably just a few degrees off, but not too much.
"It might get to the upper 20s in some parts but it'll be a stretch to reach 30C."
Christchurch is forecast for 26C, and Auckland is in for a high of 25C, with cloudy periods and chance of a shower.
Mr Dyason said a block of high pressure to the east of New Zealand is causing the arid conditions across Canterbury and North Otago.
"It brings warm northerly winds over the South Island, and that wind just heats up a little bit as it comes over the Southern Alps."
In the lead up to Easter weekend Mr Dyason said there is "a bit of weather on the way".
"It looks to be a fairly decent front and low-pressure Tasman low moving on to the country by the latter part of this week," he said.
"It's still a little difficult to say what's going to happen over the weekend but I know the lead-up is likely going to be wet in most places."
Easter weather:
Auckland: Showers on Friday and Saturday, clearing on Sunday to be fine through to Monday, temperatures in the low 20s.
Hamilton: Chance of a shower on Friday, and showers with little wind on Saturday and Sunday. Monday is fine with a high of 23C.
Tauranga: Long fine spells and a high of 25C on Friday, showers on Saturday and Sunday. Fine on Monday.
Wellington: Showers and strong southerlies on Friday and Saturday, fine with northwesterlies on Sunday and Monday. Temperatures in the high teens.
