Niwa warned the Tasman Sea and sub-tropics north of New Zealand might also become more active heading into late February and autumn, which could increase the risk for heavy rainfall events.
But the risk of tropical cyclones to New Zealand remained near normal.
On average, at least one ex-tropical cyclone passes within 550km of New Zealand each year, bringing heavy rainfall and damaging winds.
An El Nino climate system that had been long predicted also wasn't expected to have much of an influence over the next few months.
While the ocean retreated from weak El Nino conditions last month, the atmosphere responded to warmer than average waters in the central and western tropical Pacific.
"For New Zealand, El Nino is not expected to be a significant driver of circulation and climate over the next three months, but atmospheric patterns may occasionally be influenced by the tropics," Niwa reported.
But later in the year, long-range models indicated the potential re-emergence of oceanic El Nino conditions, which suggested the potential for a "protracted" event.
"This means that above average sea surface temperatures may persist for more than a year across the equatorial Pacific."
Coastal waters around the country were already much warmer than average, with marine heatwave conditions likely being reached in the east of the North Island.
Sea surface temperatures in the Tasman Sea were also well above average, particularly in the central and west, where waters were sitting between 2C and 3C warmer than average at the end of the month.
But Niwa added that still couldn't compare with the freak marine heatwave that engulfed New Zealand during last year's record-hot summer.
For the time being, the continuation of much warmer than average seas in the Tasman Sea and in New Zealand coastal waters could contribute extra warmth, moisture, and invigorate low pressure systems as they approached the country heading into autumn.
