CLIMATE UPDATE - NEXT 4 WEEKS - WITH A GOOD LOOK AT AUGUST.

Headlines


  • Strong signals for rainfall to remain connected to the westerly wind belt over the next 2-3 weeks with moisture from the Indian Ocean bringing a chance of above average rainfall for parts of WA through southern SA and into the southeast inland.

  • Near 50/50 chance of achieving normal rainfall for large parts of the nation, away from central QLD which will stay mostly dry during the coming 2-3 weeks (at this stage).

  • Higher temperatures expected over much of the northern half of Australia, especially during the coming 2 weeks, with a persistent upper high over northern Australia.

  • Pockets of cooler weather possible over southern Australia but overall should be a much better chance of seeing average conditions for the south, with temperatures expected to exceed the norm as we get into August.


Rainfall Outlook - % chance of exceeding/not exceeding the median rainfall over the coming 4 weeks.

The signal strengthens in the data sets with most of the ensmeble members across multiple platforms suggesting wetter weather for parts of southern Australia, particularly those regions expecting rainfall this week in the winter westerly regime. This may be replicated 2 times more over the next 4 weeks and moisture from the northwest may get involved again next week and again in early August. The north has neutral odds, a slight bias towards dry over central QLD, however as we saw earlier this month, it takes one system to change these forecasts. The Indian Ocean Dipole is the big player and these falls will be connected to that driver, but it MUST be in phase with a negative SAM which brings more frontal weather towards the south of the nation.

Temperature Outlook - % chance of exceeding/not exceeding the median temperatures over the coming 4 weeks.

No significant change to the outlook for the next 4 weeks, the upper high controlling northern Australia's weather with elevated temperatures expected for the good part of the coming fortnight at least, and with the Indian Ocean continuing to warm, this will mean warmer days and nights are likely to increase in frequency up north. Over the south the winter westerly belt will feature through this period with winter outbursts, but as the south will experience this week, the cold outbreaks are not long duration. Above average temperatures may return as we end the month and begin August over vast areas of the country with signals of an early spring developing.

CLIMATE DRIVERS


Southern Annular Mode - SAM - Neutral.

The same is just into the negative zone but within tolerance to be classified as neutral. This is assisting in keeping frontal weather at average levels. With the Indian Ocean full of moisture at regular intervals during this period, the frontal weather needs to remain at average to above average levels to see the rainfall signals from the models (see below) verify across the country.


SAM Forecast - Next 10 days. Note the split in the members. That will keep the SAM in neutral territory. But it is a volatile climate driver with little skill in forecasting well in advance. So we watch trends, but for my read, it should remain neutral through next week.

Indian Ocean Dipole - Negative and continuing to deepen.

No change in the signals over the Indian Ocean with basin now much warmer than normal through the area south of Indonesia through to NW Australia, thus providing elevated moisture levels that continues to flare into convection with moderate to heavy rainfall, highly anomalous for this time of year in this region. That moisture shooting through the jet stream (as you can see today) with areas of rainfall spreading across the nation. It is anticipated this trend will not change in the coming 4 weeks or really 3-4 months.


IOD Forecast - BoM - Next 6 months. The neagtive IOD has weakened on the BoM model but other global agencies still strengthen this feature through spring and I am siding with that solution.

IOD Forecast - Global Models - October.

Note the BoM has resolved the negative IOD and more reliable Euro model continues the IOD strong through November and I will continue to side with that solution. That keeps rainfall chances elevated but will see how this looks next week when the drivers update.

ENSO - Neutral

Conditions remain neutral for the coming month or two with a cooling trend through the basin with upwelling supporting further cooling in the Nino region. Global agencies have declared a La Nina watch. The BoM has not so at this stage it is a neutral phase for the coming few months but this could change if the signals strengthen. At this stage little impact on our rainfall and temperatures are expected from this driver at this time.


A La Nina coupled with the negative IOD may increase rainfall well and truly above average for many areas this spring if this forecast verifies. So flooding may be a concern or a risk if the signal continues to grow so will have more on this next week in the latest data set update.


BoM ENSO Forecast - Coming 6 months - showing that dive towards a La Nina.

This model is not supported by all agencies but there are signs of a shift towards cooling of the basin through our spring. This is not unprecedented on the back of last years La Nina event.

Global Models ENSO Forecast - October. NOAA and other global models outside of this do suggest a La Nina developing. Curiously ECMWF also has shifted to a cooler phase in their latest update which may impact this outlook next week.

RAW DATA


Back to the next 4 weeks and clearly there is a strong trend to bring up the chance of rainfall for southern parts of WA, through SA and into the southeastern inland with frontal weather increasing and linking into moisture that will be embedded into the westerly wind belt as it rolls through the southern parts of the nation. All models are showing a very similar rainfall spread across multiple sets of members, so the agreement is good.


This is also reflected in the trajectory of rainfall through the short and medium term forecasts which an see from earlier today on this page.


Euro M 12z - Rainfall for the coming 6 weeks - Valid Tuesday 13th of July 2021.

The data sets have shifted the rainfall back to the winter westerly profile, identifying the moisture streaming through much further south meaning that the westerly wind belt becomes more productive in the next 4-6 weeks. That does not mean there won't be inland rainfall, but all of a sudden there has been a shift towards rainfall in the same areas as identified in my short and medium term forecasts this morning, continuing through next week and into possibly the first part of August. Upper ridging over the north and east may keep things dry and hot through this period, but doesn't mean that moisture cannot float through areas of inland QLD as we saw last week and at the end of June.

GFS M 12z - Rainfall for the coming 5 weeks - Valid Tuesday 13th of July 2021.

Good agreement in the GFS for the coming 5 weeks also showing significant coastal rainfall to continue and that may extend inland with moderate rainfall for WA, SA, VIC and NSW. Heavy falls across coastal areas of SA, VIC and WA also likely in the persistence signal of westerly winds, frontal weather, high levels of moisture being embedded into the flow during the course of the next 4-6 weeks. Again that doesn't mean there is no chance of rainfall increasing over inland QLD during this time, but we need to monitor the moisture spread during the coming weeks as one offshoot could be collected by a trough over inland areas over the east and north and produce rainfall, especially if the SAM turns positive.

Euro M 12z - Rainfall Anomalies for the next 5 weeks - Valid Tuesday 13th of July 2021.

Drier signals over the interior and along the east coast at this time of year is climatologically expected being it is the driest time of the year through these areas so nothing outrageous here. The more impressive signals are along the southern coastlines with widespread above average anomalies for the coming 5 weeks. Some areas over southeast SA and northeast VIC, southeast NSW could see 100-150mm above the norm for this period, even if we see half of these values, that is significant in itself being that it is a wet season for these areas. The wet signal continues for WA and does increase over SA which is welcome if it verfies.

GFS M 12z - Rainfall Anomalies for the next 6 weeks - Valid Tuesday 13th of July 2021.

GFS much drier through the nation and has ran far too dry this year but the similar signals are expected for the southeast and throughout the southwest. Dry signals over the north and northeast in the dry season nothing outrageous. Looking wet over TAS which is significant when rainfall is in the order of 200-300mm through this period.

The Seasonal Outlook shows widespread above average rainfall over Indonesia that will fuel the moisture streaming southeast and south through the jet stream bringing up rainfall through the coming period beyond this 4-6 week window. So the wet signals continues.


Euro Rainfall Outlook - Seasonal Forecast August-October 2021.


Temperatures are largely unchanged from the last update.


Euro M 12z - Temperature Anomalies for the next 5 weeks - Valid Tuesday 13th of July 2021.

Warming trend over the coming 4-5 weeks and this I believe is closer to the truth with more rainfall expected over the southeast and south of the nation, back to the southwest, near normal temperatures are likely. The heat is building over the north and modelling in the short and medium term support the heat being more amplified just north of the jet stream through northwest WA.

GFS M 12z - Temperature Anomalies for the next 5 weeks - Valid Tuesday 13th of July 2021.

A warmer four to five weeks on the way, I had thought that this model was running a bit too hot, and it possibly is, but there is now an argument for the early spring debate to be had, given that there are above average temperatures being observed over large parts of the north this week, this could filter southeast and east with the zonal flow and upper northwest to westerly winds.

LOOKING A LITTLE FURTHER OUT.


I mentioned above that the Euro is now indicating a stronger signal for La Nina and the neg IOD overlapping during the Spring. This is quite a shift in recent weeks with the model continuing to show a wetter signal over larger parts of Australia. While the BoM have not issued that forecast, their rainfall outlooks are extremely aggressive (way more aggressive than mine).


There are mixed messaging out there, the bottom line here is that the negative IOD will continue, and likely peak in the Spring and the ENSO may shift to another La Nina during Spring through Summer.


The Climate Prediction Centre/IRI ENSO Member Forecasts -Valid July 8th 2021.

Many members are now indicating a La Nind during the summer in Australia which wanes through Autumn next year. This is the catalyst for a La Nina watch being declared last week by some global weather agencies.

Here is the data split on the ENSO Forecasts, showing the bias towards a La Nina. There is a very small chance of an El Nino over the coming 10-12 months.


Into spring - note the cooler than normal SSTs off the coast of South America, not overwhelming but a cooler trend none the less, and the warmer bias off northwest Australia that is allowing the moisture to keep streaming south and east through winter and most of spring, elevating rainfall chances across the nation.


Euro SSTs anomalies - Seasonal Outlook for July through October 2021.

Euro SSTs anomalies - Seasonal Outlook for September through November 2021.

Euro Rainfall anomalies - Seasonal Outlook for September through November 2021.

Rainfall anomalies remain elevated over large parts of the nation for Spring. Some flooding issues may develop after what has been a wet 18 months for the eastern inland. Note the early onset rainfall too over the north.

More climate details to come on Friday and I will be doing more analysis this week on the climate drivers just to give you all an indication as what to expect from the drivers through different times of the year.





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