The North Island could be battered by up to two tropical cyclones over the coming summer.
Forecasters across the Southwest Pacific show many countries in the region have a higher-than-usual risk of category 3 or higher cyclones from November to April.
Oceanic and atmospheric forecasts show La Nina conditions will likely develop, which consist of below-average sea temperatures in the Pacific.
Niwa scientist Chris Brandolino said this would bump up the likelihood of cyclones.
"For the whole season, my expectation for the upper half of New Zealand is for an above-average cyclone risk."
Cyclones can cause significant wind, coastal damage and rainfall over a larger area than that directly hit by the system.
Vanuatu, Fiji and Tonga could be hit by two or three cyclones, and New Caledonia faces the risk of up to four cyclones.
Cyclone Cook devastated Bay of Plenty town Edgecumbe in April, and floods caused chaos in the lower South Island in April.