"We don't know, at this stage, if it will reach warning criteria - which is 100mm of rain in 24 hours - but there will be a lot of rain. And while it may not reach warning levels, the accumulation of three days of heavy rain could cause surface flooding or bring down slips across the north," Murray said.
"There will also be gale force winds to contend with over the next two to three days."
She urged people to stay up to date with the latest weather forecasts, and check for any weather warnings, as the situation could change rapidly.
The Tasman Tempest is expected to hit the South Island first this afternoon, bringing heavy rain and strong winds, hitting the West Coast hardest. A low is then expected to develop and bang head-on into the North Island late Friday night, and into Saturday, from the northwest.
Despite the forecast rain and wind, the temperatures in Northland over the next few days are expected to stay in the normal range for the time of year, Murray said.
She said the average April high temperature for Whangarei was 20.5C, in line with the highs experienced so far this month. Whangarei's hottest April temperature was 26.6C in April 1995.
Temperatures are likely to drop further during May as winter approaches.
