Wednesday, October 4, 2023

MetService - Monthly Outlook - October 2023


Climate Drivers – Strong El Nino in place

Sea surface temperatures in the equatorial Pacific Ocean NINO3.4 area now exceed 1.5C degrees above average, meeting the strong El Nino criterion. All climate models strengthen the event further, between now and its likely peak around Christmas, with the majority of models forecasting an intense El Nino event for summer.


In addition, a positive Indian Ocean Dipole event is now underway, which typically enhances the westerly flow of weather across New Zealand. The Southern Ocean should also periodically throw some stormy, cold, and unsettled bursts of wind and weather across the South Island through October, reinforcing the westerly pattern.


Due to the windy September, the local Tasman Sea marine heat-wave has now ended, with sea surface temperatures currently near average, to a touch cooler than average, around the New Zealand coastline. This means that a marine heatwave will NOT be factor in our late spring or early summer weather patterns.

October 2023  – Often cold & windy, with El Niño westerlies

The hallmark of El Nino in New Zealand is a cold spring.

August ran much colder than usual, nationally, and the forecast for October is also much colder than usual. Expect a colder than average October across the country, with the exception of Nelson, Marlborough, Canterbury, Gisborne and Hawkes Bay. In those regions, monthly temperatures likely end up ‘about average’ BUT expect abnormal spring temperature swings between extreme heat during foehn warming in the westerlies, and intermittent cold blasts and even some high-country snowfalls.

This week, high pressure brings a relatively dry week. For the rest of October, a stronger than normal ridge is predicted over Northland, coupled with stormy, unsettled westerlies across the South Island. In between, stronger than usual westerlies are forecast – it looks likely to be a windier than normal October.

Rainfall is expected to be normal to above normal along the West Coast South Island, and in Southland. For regions in the northeast of both Islands, below normal rainfall is forecast (Northland, Auckland, Coromandel, Bay of Plenty, Taupo, Waikato, and Waitomo, also Nelson, Marlborough and Coastal Canterbury). For Gisborne and Hawkes Bay, a burst of rain this weekend is then followed by drier westerlies (e.g. normal to below normal rainfall for October as a whole). Elsewhere, near normal October rainfall is forecast.


Pigeon Post News, Richmond.

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