ENSO UPDATE - LA NINA - ON OR OFF FOR SPRING OR SUMMER?

And what does it mean for you? it is all good and well to have the declaration of these climate drivers being in phase for rainfall, but for parts of SA and QLD, there has been some gnashing of teeth and frustration as the Indian Ocean HAS been declared in a negative phase by some models since June, and was expected to bring above average rainfall influence but that has not been verified for some areas, but for others, they have been swamped with many locations passing their yearly rainfall totals already.


However, that said, we have to deal with the data and respond to it accordingly and though it is not my job to manage your expectations regarding what you want from La Nina, it is about facts and dealing with data and providing you that information and what YOU NEED TO KNOW.


HEADLINES


  • La Nina chances remain at 79% chance of occurring in the Pacific Ocean from October 2021

  • La Nina peaks in late December or January IF it develops.

  • The event being declared underway does not mean that it begins from that moment, the impact of La Nina lags up to 4 weeks from developing in the oceans. The atmosphere then responds. That is also true in the waning of an event.

  • La Nina does not impact the same areas the same way every time and it DOES NOT GAURANTEE WIDESPREAD RAINFALL FOR EVERYONE!

  • The bias of influence is over northern and eastern parts of the nation with less impacts for parts of SA and WA.

SPRING FORECAST - RAINFALL AND TEMPERATURE OUTLOOKS - Valid August 28th 2021

THESE FORECASTS WILL BE UPDATED FRIDAY.

Rainfall Outlook

% chance of exceeding the rainfall for Spring 2021

Temperature Outlook

% chance of exceeding the temperatures for Spring 2021

SUMMER FORECAST RAINFALL AND TEMPERATURE OUTLOOKS

Rainfall Outlook

% chance of exceeding the rainfall for Summer 2021

Temperature Outlook

% chance of exceeding the temperatures for Spring 2021

LA NINA CHANCES

The chance globally of a La Nina developing in the Pacific Ocean is sitting at 79% over the course of late Spring and into Summer 2022. There is a 21% chance of a Neutral phase remaining in place for Spring and Summer 2022. There is less than 1% chance of an El Nino.

DATA SETS

The CPC ENSO Forecast for September had increased the chances of a La NIna and other agencies have now jumped on board this off the back of recent data that has come in over the past 4 days. The chances of a La Nina is VERY HIGH, but still need a few more weeks of data to then adjust forecasts for Spring and Summer with greater confidence. The event may exceed the strength of the previous La Nina event which caused significant flooding over the east after a similar dry winter last year, these areas turned very wet very quickly. It also kept summer heat moderate and the monsoon was very productive, though cyclone activity was below average.

This is the Seasonal Spread of data showing the bias towards the La Nina, possibly developing during late October into November. This event looks to then resolve by the end of February in line with climate expectations. The strength of the event once it is declared a La Nina phase will be something that evolves very quickly. I will note, that even though we are staring down a La Nina this summer, this does increase the risk of an El Niño forming next Spring and Summer 2022/23. So will have to look at that in greater detail in the weeks ahead.

SSTs Anomalies throughout the Pacific.

So this again is a snap shot of the basin being relatively near or below average, the exception closer to South America. That said the anomalies run quite deep through the Nino 3-4 region and they have not recovered enough since the last event, now triggering a rebound event, very common to see two events back to back.

Sub surface Temperature Anomalies.

Depth on the left hand side and the region runs along the bottom. You can see the anomalies are quite cold towards the central Pacific and warmer SSTs towards Australia, which is supportive of above average rainfall through the remainder of the year for QLD and NT, extending south and west through eastern Australia. Higher SSTs means elevated moisture levels that get drawn through the trade winds across the eastern inland into the south and southeast ahead of cold fronts. We saw this take place earlier in the month, the influence of the trade winds into a strong trough which brought that soaking rainfall over NSW and VIC, but piggy backed SA.

SSTs as they stood at the start of the month - September 1.

Note the warmer waters over northern Australia and off QLD. This is a signal that the basin is primed for a La Nina to form given the sub surface temperatures we observe above.

Trade Winds

Trade winds have been strong west of the date line for a while now, and we have seen that impact areas of northern QLD with heavy rainfall, above average winter rainfall along the coast. It may be drier this week as the trades have eased, but these winds are likely to become entrenched through October, continually feeding the tropics with moisture and this seeing the wet season start early and become quite productive in terms of rainfall. This then influences rainfall chances throughout the Spring as we get warmer.

Southern Oscillation Index.

This has been remaining positive throughout the year since the last La Nina, which you can see in January. I will mention that the La Nina potential is coming off a higher base than last year. This tends to see the second year event be stronger than the first and have a larger influence for a longer period. But not one event is ever the same, so will have to watch trends, but that is a very general rule.

MODELS

Global Climate Agencies Spaghetti Plot

This was August Plume of the Climate Models and they have adjusted further below neutral hence the increasing likelihood for La Nina conditions this Spring and Summer. I think we will see these models render further below the neutral zone in the September Update due soon. A couple of statistical outliers from IRI is suggesting a very strong event, however this has not changed its plot, it is the other climate models that have moved closer to that outlier, which is something to watch at the next update, because then you can start forecasting strength and then impacts with a bit more certainty.

BoM POAMA Spaghetti plot -September 14th.

Note the shift now into a modest La Nina event, the average, black line, of all the models is the one to watch. They are much more tightly clustered now under the threshold. Only a few remain in the neutral zone which is good agreement against the data above.

Global Modelling Plots

October 2021

The event according to some models should be close to underway if not underway through October. The one model to watch closely for the strength and depth of the event is NOAA. It has been the only model to pick this back in June, for as long as this site has been up and running. We have profiled that for many months now and it appears that other agencies are playing catch up. The other model to watch is the Euro in the coming weeks, that has started to move towards La Nina however does not quite reach that status.

November 2021

The event is well established according to 5/7 models with the agencies that I also would like to see confirm a La Nina not so keen on that idea - so watch this space.

December 2021

The event should begin to peak during this month, the NOAA has very robust values and if this was to verify, in combination with a waning negative IOD, it could be a very wet period for the nation from October through the end of the year. Otherwise most global agencies have a modest event at this time.

January 2022

The La Nina continues to hold it's strength through January, may also peak through this month rather than December, though there has been a bias in the pages of data sets I have reviewed for the event to peak earlier than last year. We will see. NOAA keeps the event very robust through the month, which again is not implausible given the current state of the sub surface temperatures of the Pacific Ocean.

February 2022

The event should be well and truly waning through February given the climate expectations, however the NOAA model is robust for February and keeping the event going into Autumn could prove to bring well above average rainfall for the coming northern and eastern parts of the nation into Autumn, which could see early Autumn breaks for the south.

There is a lot of information here to go through but I am bringing you the most important details for now, and again this is not me forecasting LA NINA developing late this season, but the chances are increasing and as mentioned, I like to review the data sets coming into October before declaring it an event, where some people interpret yesterday as it being declared.


It is not a declared event! It is a signal and we all know how the modelling has been of late, so caution is required and professional and skilled interpretation of data sets is required and then tabled into a package above.


I will update my SEASONAL FORECASTS on Friday.



Before I finish, The Indian Ocean Dipole event has been declared over by the BoM model however the international modelling, which is the set I am leaning with strengthen the phase over October and November before it resolves in December. That is the appropriate forecast, always has been if you have been following for months, the event was never active July or August as per the BoM model.


BoM Model - Climate Set

This is not the model I am supporting at this time, this model has been volatile, and two updates ago, had a negative event of -2 for the month of October, that is an error rate of nearly 2, which is quite poor.

International Models

Note the phase is expected to peak during October with all climate agencies supporting the strengthening of the IOD from now until the end of October before it weakens in November and resolves December as you can see below.

November 2021

December 2021

Simulated Cloud Forecast

Simulated cloud cover shows that connection from the Indian Ocean to weather systems moving across the nation, surging southeast through the nation in the upper northwest flow.

Precipitable Water Anomalies

Note the influence increasing from the Indian Ocean in the next fortnight which goes against the IOD weakening.

More to come this afternoon in your state based forecasts.


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