CLIMATE UPDATE - REMAINDER OF JULY - LETS HAVE A LOOK AT AUGUST THOUGH OCTOBER AS WELL.

Headlines


  • A wet signal continues for the coming 4 weeks for many parts of southwest and western Australia in line with the current medium term forecast with heavy rainfall and frontal weather to continue. This will spill over into the southeast with coastal areas likely to build in rainfall totals over the coming 10-14 days.

  • Slight bias of above average rainfall for inland parts of Southern Australia which may increase in chance if a northwest cloud band can bring widespread falls in the coming 2 week period while the westerly wind regime is active under a negative SAM and negative IOD.

  • Warmer than normal over northern Australia with a flip of the coin chance of seeing some dry season rainfall over the coming 4 weeks, but there is no bias.

  • A colder than normal signal continues for southern parts of the nation in line with the northward spread of the westerly wind belt over the coming 10-14 days. This may extend into southern QLD.

Rainfall Outlook for the coming 4 weeks - Valid Tuesday 6th of July 2021.

Slight bias for above average rainfall over eastern parts of NSW and into QLD with a lingering trough later this week but some areas have already seen above average rainfall for the month on the back of last week. Rainfall should increase over the southeast through the next 2 weeks with another wet 2 weeks to follow as we enter August. The frontal weather will persist over WA with a bumper wet season for the west coast to continue. Neutral odds for drier/wetter weather over the inland areas, and the wild card in play will be the northwest cloud bands that will develop over the next 4 weeks.

Temperature Outlook for the coming 4 weeks - Valid Tuesday 6th of July 2021.

The continuation of above average temperatures for the north of the nation with more humidity expected to feature especially in the second fortnight in this outlook. The cold bias is connected to the frontal weather over the southern parts of the nation with that bias continuing for the next fortnight, with temperatures likely to recover in the second fortnight, if the westerly wind belt relaxes, which is more likely than not.

CLIMATE DRIVERS


SOUTHERN ANNULAR MODE (SAM) : Trending neutral this week but forecast to shift negative by the weekend and through next week. That means more frontal weather is likely to impact the south next week with colder than normal weather and above average rainfall chances more likely. The SAM could persist in the negative range for 7-10 days taking us through to mid month, before retreating to normal values. But this is an erratic driver to forecast beyond 10 days so caution is advised.

SAM Forecast - Next 2 weeks - note the secondary surge with some members going well lower into the negative territory which brought the severe weather for southern parts of the nation during early June.

INDIAN OCEAN DIPOLE (IOD) : Remains negative and deepening in the negative range with the waters continuing to warm. We can see that present in the current moisture content, above average convection rates and precipitation observed out in that northern basin. This will play a bigger part in the outlook from August through November. This will contribute the wetter bias as we go through towards spring 2021.

BoM Model Forecast - This will be updated later today - but I am expecting no change to the forecast.

ENSO - La Nina/El Nino: Neutral values to continue though the rumblings of a La Nina developing in the spring through summer do continue, more on that on Friday, but I am still forecasting cool neutral conditions. This has limited influence on the national weather.

BoM forecast model for the next 6 months for the Pacific Basin (NINO 3.4 region) - this forecast also updates this afternoon, I am not sure where the model will go but I would think the cool neutral outlook is the right one over a La Nina, more on this on Friday.

MODEL DATA - VALID TUESDAY 6TH OF JULY 2021.


Rainfall Outlook for the next 4-6 weeks.


Euro 00z run - Rainfall anomalies for the coming 4 weeks to the period August the 4th 2021.

No change really in the overall model runs. The ensemble below still giving well above average rainfall for the southwest which eventually spills over to the south then southeast later in this period, which is lining up with the shorter and medium term forecasting, so I would continue to align myself with this outlook. The drier bias for the inland is negligible when this area receives little rainfall. The dry bias over QLD is connected to the persistent westerly wind flow which will dominate the coming 2-3 weeks at least. Rain may come back in the last week for the region.

GFS 00z run - Rainfall anomalies for the coming 4 weeks to the period August the 3rd 2021.

This is way to dry for the nation and I am throwing it out, but good to compare.

Temperature Outlook for the next 4-6 weeks.

Euro 00z run - Rainfall anomalies for the coming 4 weeks to the period August the 4th 2021.

A warmer bias exists for the northwest and north of the nation, and this may drift down through the last week of this period, but I am still standing by a cooler than normal period of weather for the southern half of the nation with the northward movement of the westerly wind belt. The temperature anomalies over the northwest are notoriously difficult to predict ahead of time given that northwest cloud bands are a chance of developing and lingering, bringing well below average temperatures, so this is low confidence forecasting.

GFS 00z run - Rainfall anomalies for the coming 4 weeks to the period August the 3rd 2021.

Running way to hot for a lot of the nation, the cool bias I agree with over the southeast and southwest but that will be extended further north through the country, with the warmer values likely to return during the last week of this month into early August over the south with a good chance the westerly wind belt retreats south with the climatic fluctuations in the SAM.

Lets look ahead to August through October 2021.


Seasonal Rainfall Outlook August through October 2021 - Valid Tuesday 6th of July 2021.

A very strong bias for above average rainfall through this period with the peak of the negative Indian Ocean dipole and with the nation warming up, more inland troughs are likely to form in response to that. Also the clash of the seasonal shift takes place, with the cold air meeting much warmer moist air, this providing more dynamics for longer and heavier duration rainfall events, based off the current climatic driver outlook. Higher humidity values over the north and an early build up likely to result in above average rainfall kicking off in September for parts of the NT and QLD.

Seasonal Temperature Outlook August through October 2021 - Valid Tuesday 6th of July 2021.

The bias for above average temperatures will continue through northern Australia with the Indian Ocean, Timor Sea, Arafura Sea and the Coral Sea likely to be above average so that means warmer days, warmer nights and more humidity leading to elevated day time and night time temperatures. Over the south the risk of either cooler or warmer than normal weather is neutral but a bias of colder weather is appearing on the climate forecast models for inland NSW in response to that above average rainfall signal for the interior parts of the nation, stacking up against the western slopes.

THE RAW DATA UNDERPINNING THIS FORECAST.


IRI Multi agency % forecast of above or below average rainfall for August through October.

The highly reputable Climate Agency in the world, is showing that bias for widespread above average rainfall through August and September, though less than likely chance of over parts of the southeast of SA and southwest WA. However this model didn't pick the above average falls for southwest WA all year, and predicted wetter weather for the southeast of SA, so I am going to think that there could be a skills error in these regions. Otherwise the model has verified well throughout the year away from the tropics. I am aligning with a very wet interior through to the eastern inland during this period.

Euro Ensemble - % forecast of above or below average rainfall for August through October.

Note that excessive rainfall signal for parts of the Indonesian Archipelago and descending over northern Australia and the rainfall over much of the interior being above average. That signal has been in place for 6 months for the nation and has not changed that much. Near normal values for the southern and southwest, but with so much moisture drifting around the nation, it takes one event to bring a months worth of rainfall at a time. So it is a wet bias.

Euro Ensemble - % forecast of above or below average temperatures for August through October.

A warmer bias continues for the north and perhaps over Tasmania for the period if easterly winds dominate. That eastern inland signal for below average temperatures is connected to the above average rainfall suggested by modelling. That is a strong sign of the rainfall that is possible given the climate data coming in.

The wet signal and cool signal continues for many locations into January next year.


IRI Multi agency % forecast of above or below average rainfall for September through November

Note the heavy signals over QLD and the NT, and very wet through NSW. Will keep an eye on trends, but we may have to start considering flood risks through this period, with a wet national look. I would hasten to get worried about the yellow shading over SA as it is in the medium to short term forecasting that we see how this verifies. I would think higher chances of above average rainfall do exist for inland WA through SA and into the southeast inland on current climatic drivers.

IRI Multi agency % forecast of above or below average rainfall for October through December.

The well above average rainfall signals continue as the nation warms up and the monsoon approaches. Will see how this looks in a few months time, but good to just have a peek into the longer term.

Euro Ensemble - % forecast of above or below average temperatures for November through January.

The milder summer look continues for 2021/22 which may coincide with those above average rainfalls across many parts of the nation as the IOD settles back down to neutral values. The wildcard is the La Nina, if that develops, then it could be another cool to cold summer against statistics and recent searing summers we have experienced.

The next climate update is expected Friday where I will take a look at the Indian Ocean and the Pacific Ocean a little more closely with the latest data sets coming out on those regions this week.

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