Forecasting in changing times

In the last week, Hurricane Otis hit southern Mexico with little warning, and Cyclone Lola set a record for the earliest category five cyclone in the southern hemisphere. Climate change is making work tricky for weather forecasters. What might be in store for our upcoming El Niño summer?

Last week in southern Mexico Hurricane Otis made landfall near the city of Acapulco as a category five hurricane. With wind speeds estimated at around 266 kph (165 mph) it caused huge amounts of damage and loss of life.

In part because there was so little warning.

Just 24 hours beforehand the US National Hurricane Centre modelling of then tropical storm Otis predicted max winds of about 112 kph (70 mph).

But the rapid and unexpected intensification of Otis caught everyone off guard, including the weather models.

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Is the forecasting game changing?

"You can never really attribute, you know, one single weather event to climate change. It's very difficult to do that," says NIWA meteorologist Tristan Meyers. But, he says, different recent extreme weather events in New Zealand do have the "fingerprints of climate change" all over them.

As part of his job, Tristan works on a number of different forecasts: from on demand 'now-casts' to look a few hours ahead - maybe to help Fire and Emergency New Zealand deal with spreading fires - through to seasonal forecasts across a few months to help those dependent on the weather for their livelihoods prepare for what's to come.

But the impacts of climate change are making his job trickier.

El Niño is here

There's a large patch of ocean in the Eastern Pacific along the equator where sea surface temperatures are monitored closely. Think of it as extending out from Ecuador in South America, into the middle of the Pacific.

When this patch of ocean is warmer than normal, and the air above the ocean responds, that's when the El Niño Southern Oscillation is in effect. Wind and ocean currents change, and when these changes spread out across the Pacific, it generally means more westerly winds for Aotearoa.

With El Niño officially declared as an important climate driver for this summer season, we can look at past seasons to forecast what might be coming: westerly winds that bring rain to the west coast but a drier outlook for the east of the country.

Overlapping climate drivers …

Go to this episode on rnz.co.nz for more details