"Things may change during the second half of the week but at the moment there is quite a bit of uncertainty as to how that is going to play out," he said.
"It is a fairly tricky situation, it does look as if there may be a low coming down from the tropics towards New Zealand but there is a large amount of uncertainty as to how that low is going to move."
Temperatures could reach 23C or 24C about mid-week.
"It is a relatively dry week, with not much rain expected, but I think it could be just a case of waiting to see how things play out."
Weatherwatch head weather analyst Philip Duncan said a potentially damaging tropical storm might be on the horizon. "We still have a few days to go before we can be sure this isn't just the computers over-predicting as they do from time to time, but based on the current data we could expect damaging winds, slips and flooding as a result of this low.
"The models today paint a very serious picture and New Zealanders, especially in the north of the country, should be keeping up-to-date with the forecasts."
Mr Duncan said it was too early to lock in where any potential heavy rain and wind would be, but it was "increasingly likely" a deep ex-tropical cyclone would push over, or very near, the North Island between Friday and Sunday.