NZ Weather Forum

Latest CFS has finally pulled the trigger on a strong La Nina to build from May. Lets see if ECMWF follows.

Canadians are now also jumping onboard the La Nina wagon going into Spring. EC & Access S are still looking neutral but it's certainly becoming interesting.

What could be expected seeing that it looks to be peaking during the coming winter?

A strong La Nina may cut Auckland's winter rainfall down with a milder sunnier winter.

Richard wrote: ↑Fri 07/02/2020 16:27 What could be expected seeing that it looks to be peaking during the coming winter?

Reduced westerly airflow. More anticyclones and depressions, and the consequent variable airflow which accompany them.

TonyT wrote: ↑Fri 07/02/2020 18:34

Richard wrote: ↑Fri 07/02/2020 16:27 What could be expected seeing that it looks to be peaking during the coming winter?

Reduced westerly airflow. More anticyclones and depressions, and the consequent variable airflow which accompany them.

A Canterbury snowstorm perhaps ?

i thought people didn't worry about La Nina /El Nino these days because of the "Climate Change" thingy?
Not much mention in the news like it was years ago?

NZ Thunderstorm Soc wrote: ↑Fri 07/02/2020 19:18 i thought people didn't worry about La Nina /El Nino these days because of the "Climate Change" thingy?
Not much mention in the news like it was years ago?

We haven't had a strong nino/nina event since 2015/16. Media will be all over it if it happens.

I thought the prognosis was a strong El Niño would develop this summer coming 20/21 or will it be the next summer?


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jamie wrote: ↑Sat 08/02/2020 08:21 I thought the prognosis was a strong El Niño would develop this summer coming 20/21 or will it be the next summer?


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Correct, one or the other. We usually expect a Nina around solar minimum and a strong Nino once firmly on the upswing into the next solar cycle. So it depends when the solar minimum occurs (we can only determine that retrospectively).

We haven't had a decent Nina this solar minimum, so I was wondering if we were going to see one at all. 20/21 summer would be the first summer into the new solar cycle so either then or the following summer would be likely to be a major Nino. If we do get a Nina developing the next six months then that would make 21/22 more likely to be the strong Nino season. If CFS is barking up the wrong tree with this prediction and solar cycle 25 gets a hurry along then it could be next summer, 20/21.

The BoM latest Access S run (29 Feb) has 9 members moving into the sea surface temp range of a La Nina by August. North American models continue to lock onto a strong SST La Nina in late Spring. It will be interesting on what the EC ensemble suggests at the end of this week.

Cyclone Tracy wrote: ↑Tue 03/03/2020 13:27 The BoM latest Access S run (29 Feb) has 9 members moving into the sea surface temp range of a La Nina by August. North American models continue to lock onto a strong SST La Nina in late Spring. It will be interesting on what the EC ensemble suggests at the end of this week.

Does cooler SST’s with a La Niña generally mean a colder winter for New Zealand does anyone know?

Bradley wrote: ↑Tue 03/03/2020 16:07

Cyclone Tracy wrote: ↑Tue 03/03/2020 13:27 The BoM latest Access S run (29 Feb) has 9 members moving into the sea surface temp range of a La Nina by August. North American models continue to lock onto a strong SST La Nina in late Spring. It will be interesting on what the EC ensemble suggests at the end of this week.

Does cooler SST’s with a La Niña generally mean a colder winter for New Zealand does anyone know?

Check out the SST map Mr Tracy posted. We usually see warmer than normal SSTs around NZ in La Nina times. That contributes to increased storminess, which breaks down the westerlies. So fewer cold southwest airflows, but potential for cold southerly outbreaks further north than usual. Overall though, Nina winters are warmer than normal due to increased cloudiness reducing night time cooling and frosts.

I would seriously say that warmer is the new normal now.

Chris W wrote: ↑Tue 03/03/2020 20:23 I would seriously say that warmer is the new normal now.

Normal is an illusive concept - its ALWAYS changing. ENSO is not known as the planet''s thermostat for nothing!

global warming is continuing to happen (there is still ups and downs with that but the trend is still up) so yes more record max temperature readings
will be broken over the coming decades (compared to record cold temperatures...i.e you still get the extremes in weather up and down, but the background warming offset means more max temperature readings are broken more and more)

CFS still wants to bring in a decent sized La Nina by mid winter (July below) and keep it going to the end of the year. That would mean no El Nino summer for 20/21 (so more likely to rebound to that for the 21/22 summer). However, ECMWF only sees La Nada through winter, and there is no sign of it getting colder in Nino1+2 yet. Still, a wait and see game for now.

NIWA going the other way, pointing to El Niño potential from around June, with rising air near Mexico and descending air around the western Pacific:
https://niwa.co.nz/climate/seasonal-cli ... -june-2020

I think NIWA probably meant the current ENSO-neutral conditions tending towards El Nino lasting until June, before leaning more towards La Nina after that, which is more in line with BoM's longer-term outlook.

From NIWA's April-June Outlook link above:

According to the consensus from international models, ENSO-neutral conditions are very likely (81% chance) for the April–June period. For the July–September and October–December periods respectively, the probability for ENSO-neutral conditions is 53% and 38% with the probability for La Niña increasing to 35% by October–December.

BOM now mentioning the possibility of La Niña and a negative IOD:
http://www.bom.gov.au/climate/enso/

BoM's statement is continuing to be backed up CFSv2 runs. This is starting to look like a 2010/11 IOD and La Nina signature if they verify. Major floods for Australia, significant South Pacific cyclones.

2010 and 2017 are the two prime analogue years I have been working off for winter/spring forecasting, also 2007 and 2013 to a lesser degree.

SST's falling off the cliff in the central tropical Pacific.

The current speed at which the upper ocean temperature is dropping in the central equatorial pacific is almost identical to April / May 2010.

NIWA tweeting a 1.2C cooling graphic today for the central Pacific and they’re going further in on La Niña. Seems very likely.

BOM sitting on the fence a little more on that and the IOD http://www.bom.gov.au/climate/enso/index.shtml