The Seasonal Climate Outlook for October - December.

- Moderate La Nina conditions continued during September and there was a strengthening marine heatwave (MHW). Both are expected to influence the climate over the next three months

- Air pressure is forecast to be higher than normal over the next three months, with the potential for longer dry spells in western areas

- Rainfall will be varied across the country, with the risk of the occasional sub-tropical to cause heavy rain in the north and east of the North Island

- Increased risk for early-season tropical cyclone activity in Southwest Pacific

- Temperatures are likely to be warmer than average across the country, with variability in October before a marked rise in November and December, along with an increase in humidity

More information about the marine heatwave:

- New Zealand’s coastal water temperatures remained above average during September, with anomaly values increasing in 4 out of 6 climate regions

- The MHW signal was amplified in climate model guidance issued in September, showing a sharp increase in SSTs from October-December

- Overall, it implies that MHW strength could rival that which was experienced in 2017-18 and 2021-22

- Given the high-impact nature of recent summer marine heatwaves, the marine sector should monitor this situation closely. For more information, see the NIWA Sea Surface Temperature Update.

- La Niña strengthened over the last two months and is very likely to continue over October-December

- This will likely culminate in the third La Niña summer in a row, a "triple dip" - while no two La Niña events are the same, there may be some similarities with last summer, which featured widespread hot and humid conditions, a marine heatwave, drought in the lower South Island, and several ex-tropical cyclones passing near New Zealand’s coasts

© Scoop Media