"With that, it's going to be bringing widespread gales, areas of heavy rain, and even possibly some good snow dumpings.
"Which of course can catch people off guard this late in spring."
The only good news is for Canterbury and Hawke's Bay, which are both sheltered from the rain this weekend.
"Today, Napier and Hastings are warmer than the Cook Islands, which is a nice victory for them," McInnes said.
"So Canterbury and Hawke's Bay are the places to be this weekend because they're really in the shadow of the ranges which protects from that rain."
For the low that arrives on Tuesday, McInnes said it was too early to say which would be the best and worst spots around the country.
The main centres
Auckland: Occasional rain, with possible heavy falls, easing tonight. Northwesterlies. High of 21C, low of 15C.
New Plymouth: Cloudy, possible drizzle. Light northwest. High of 18C, low of 12C.
Napier: Fine, high cloud. Northwesterlies. High of 27C, low of 14C.
Wellington: Cloudy periods. Strong, gusty northwesterlies. High of 18C, low of 13C.
Christchurch: A fine day. Strong northwesterlies easing this evening. High of 24C, low of 8C.
Queenstown: Often cloudy, possible shower. Westerlies strengthening. High of 18C, low of 5C.