"We're not at the panic point yet, but we are at a crucial stage. It's verging on becoming a serious problem."
Mr Doolin said a weather system currently moving up the country was bringing a lot of rain to western areas of the country.
"That should ease from the south of the South Island tomorrow evening, but going into the rest of the week it should be more showery in the west coast of the North Island and clearing up on Tuesday and Wednesday along the east coast.
"But there's still going to be a bit of precipitation around on the west coast of the North and South Island in the earlier part of the week.
"Later in the week there's going to be more showers developing, which will be more widespread.
"Basically, it's going to be not as good as it's been recently."
Auckland could expect occasional showers this evening which would continue through tomorrow, Mr Doolin said.
"It may be easing later in the evening."
Temperatures would stay in the early to mid-20s across most of the country this week, he said.
A full forecast had yet to be established for Waitangi Day on Friday, but widespread showers could be expected for most of the country in the afternoon.
Meanwhile, an online WeatherWatch poll found 26 per cent of respondents were sick of the heat and missed winter.
The poll also found 67 per cent of respondents enjoyed dry heat, compared with just 7 per cent who said they preferred more humid conditions.
TOMORROW'S WEATHER:
Whangarei: Fine spells and few showers, northeasterly turns northwest. High 29C, low 19C.
Auckland: Mostly cloudy, occasional showers, northeasterly turns northwest. High 27C, low 19C.
Hamilton: Occasional rain, possibly heavy in the afternoon, with light winds. High 25C, low 17C.
Tauranga: Occasional rain with northwesterlies. High 25C, low 20C.
Wellington: Rain leading to afternoon showers, with northwesterlies gusting up to 100km/h at night. High 22C, low 17C.
WAITANGI DAY FORECAST:
Whangarei: Rain with southwesterlies. High 24C, low 16C.
Auckland: Rain with southwesterlies. High 21C, low 15C.
Hamilton: Partly cloudy with southwesterlies. High 22C, low 10C.
Tauranga: Fine with westerlies. High 23C, low 14C.
Wellington: Fine with westerlies. High 17C, low 13C.
(Source: MetService)