El nino can spark a mix of bizarre weather conditions.
Since our last update in The National Farming Review, El Nino conditions have reached very strong levels in the central Pacific Ocean.
The pool of abnormally warm seas centred on the equator now extends right across the Pacific Ocean, from South America to Vanuatu. Sea temperatures in August across the central Pacific exceeded 2 degrees above normal. It is the strongest El Nino since 1997/98 by all indicators.
You may hear mentioned that the 2015 El Nino event has equalled the 1997/98 event. This refers to the fact August conditions were comparable between both events. But the 2015 version has not yet reached the peak seen in 1998 -- it is, however, intensifying a bit earlier in the year.
Recently, the atmosphere and ocean have been working hard together, in a somewhat vicious circle, to continue warming the seas and strengthening the event. In other words, this El Nino is locked in, and is likely to persist through into the first quarter of 2016. A maturing of the El Nino is expected in the coming few months. The latest forecasts predict this El Nino will strengthen further between now and Christmas, but at a more modest pace than recently seen. It is expected that this event will peak around December and then rapidly ease during autumn 2016.
Recently, the atmosphere and ocean have been working hard together, in a somewhat vicious circle, to continue warming the seas and strengthening the event. In other words, this El Nino is locked in, and is likely to persist through into the first quarter of 2016.
Importantly, it is by no means certain it will reach the 'super El Nino' levels seen in 1997/98 and 1982/83. During those events, seas approached 3C above normal in the central Pacific, and exceeded that in the eastern Pacific. Even if it does, there is no guarantee that we will see 'super' (extra strong) impacts here in New Zealand. It is useful to note that the effects in New Zealand of the 1982/83 and 1997/98 El Nino events differed greatly over the summer period . The summer of 1997/98 was strongly anticyclonic, with much higher pressures over all of New Zealand, and frequent west to northwest winds over the country.
In comparison, the summer of 1982/83 was stormy, with low pressures and frequent southwest winds over New Zealand. Not surprisingly, summer 1997/98 was unusually hot and dry, while summer 1982/83 was unseasonably cold.
The detailed monthly forecast can be found at www.metservice.com/rural/monthly-outlook. This is a good place to find out which weather patterns will be important in the short term.
The extended easterly rain event at the end of September, which produced significant rainfall for the drier eastern regions of both islands, certainly highlights the fact that weather will trump climate any day.
But longer term, El Nino remains our strongest influence at present. As a first guide for longer-term planning, remember that El Nino conditions
Roughly double the odds of a cold spring for all regions.
Increase the odds of a dry springfor the western North Island and northern South Island.
Increase the odds of a dry summer for the north and east of both islands.
There is no guarantee that the El Nino of 2015/2016 will play out along typical lines. However, so far, impacts throughout New Zealand are doing all the 'right' things. Namely:
Sea temperatures around the New Zealand coast are running cooler than normal (especially to the east of the country).
Air temperatures for the back half of winter, and also for September, were below average for most regions.
Southerly air streams were frequent during the back half of winter and also September.
Soil temperatures were well down compared to normal in August and September for many regions, but most markedly in the southeast South Island.
MetService will continue to monitor this El Nino and provide regular commentary to farmers through the monthly Rural Outlook, and our social media channels (@MetService on twitter and MetService New Zealand on Facebook).
We're happy to answer questions you have on how this El Nino is tracking.