Reading Time: 2 minutes Waiting for El Niño to develop is like watching a heavy truck drive up a mountain highway. You know it’s on the way, but it’s slow going. For us in New Zealand there are two ways to look at El Niño. There is the global view, where we look at the entire Pacific Basin and judge whether or not El Niño will be moderate, strong or severe, then there is the local New Zealand view, where we work out what this
means for us weatherwise. Most of the headlines you’re seeing are from the Pacific-wide point of view and because NZ is a couple of mountainous islands halfway in the Roaring Forties belt of weather, which circles Antarctica, it is harder for us to be specific about what this means for NZ. At the timing of writing this we are still in a neutral weather pattern, but in the tropical Pacific El Niño edges closer. Australia’s Bureau of Meteorology (BoM) says that “sea surface temperatures in
the central tropical Pacific now exceed El Niño thresholds, while atmospheric indicators are also starting to align with an El Niño state. This suggests some coupling between the ocean and atmosphere may be occurring. Should this be sustained, an El Niño event is likely to become established.” In its fortnightly Southern Hemisphere update BoM says: “Atmospheric indicators, such as trade winds, pressure and cloud patterns are trending towards an El Niño state. “Some uncertainty remains in the likely strength of this El Niño event. Models
indicate it will be at least moderate in strength, with the possibility of a strong event, based on the extent of warming in the central tropical Pacific.” As I’ve pointed out in previous weeks, as has BoM, a strong El Niño north of Tahiti does not always mean a big shift to Australia’s climate, or New Zealand’s, but the recent uptick in high pressure since late April may well be a sign of what is developing in the tropics. NZ has had a lot of
high pressure, which has lead to a widespread drying out of regions across New Zealand. NZ has a couple of cold fronts this week, but our weather is still mainly dominated by high pressure. By Monday of next week longer-range modelling was suggesting a bigger cold front spreading up NZ with polar air – but it’s worth noting this may be caused by yet another very large and strong high-pressure zone around Tasmania. Strong highs west of NZ and placed over Tasmania with the right
shape help dredge up our coldest airflows, but even when those southerlies bring in some northern and eastern wet weather they do tend to push most of the rain on to the West Coast. Because we’re still technically in a “neutral” pattern we’re still getting some variety in our weather, but the forecast rain maps continue to show most rain falling on the West Coast, with limited rain for the North Island and eastern South Island.
El Niño, New Zealand weather, high pressure, cold fronts, West Coast rain, Southern Hemisphere update, trade winds, sea surface temperatures, tropical Pacific