MEDIUM TERM FORECAST UPDATE.

No real change in the short term, still expecting the frontal weather over the west of the nation spreading east through SA and into the southeast states from mid this week and then sweeping into the southeast over the weekend with light to moderate rainfall.


Rainfall for the next 5 days - Until Sunday morning.

Rainfall is concentrated for the east coast with onshore winds driving in light showers about, more concentrated over the northeast of QLD. Then showers increasing mid week for WA, that activity spread again to SA and then the southeast states Friday into the weekend. Moderate falls are possible over the southwest of WA, southeast of SA, southwest of VIC, northeast Alpine areas of VIC into southeast NSW. Heavy falls possible for western TAS. Fine and mostly dry weather for a lot of the inland.

ICON 18Z - Rainfall for the next 5 days

This is a fair representation of the rainfall spread for the coming 5-7 days with much of the nation under the influence of high pressure bringing above average temperatures. The weather over the southeast and south, through the southwest turning showery with frontal weather. The more complex system that we are covering off below comes from Sunday through early next week and then the follow up rainfall opportunities to the end of the month.

Next week, the complexity continues, you can catch the earlier data sets in the morning state based forecasts to compare with this latest data.

18Z GFS Surface Pressure Pattern for the coming 16 days

The GFS in the medium term has multiple low pressure systems passing through during the coming 2 weeks over the southern and eastern parts of the nation. This means rainfall will fluctuate from one run to the other as systems come and go from the modelling. The system next week is not as potent as this morning, but the Euro data set is much more aggressive than the earlier run which was available via the yr.no and other apps this morning so just standby for more significant changes to the forecasts coming up in the days ahead. For now, there is follow up rainfall for the southern parts of the nation, with limited activity expected to filter through inland areas for now, but the easterly wind shift at the end of the period could change things for QLD and NSW.

18z GFS Precipitable Water Anomalies next 16 days

You can see that moisture surge IF the winds do veer into the east later in the run for the eastern inland of the nation, so that is worth watching in the coming days in these daily updates to see if that continues to be a trend. Right now the drier air kicking through the nation is winning the battle on the modelling this morning for the medium term over central and northern Australia but that could change again in the coming data, so low confidence continues in the forecasts.

18z GFS Rainfall for the coming 16 days

And the rainfall output for the coming 2 weeks taking us to the end of the month reflects that coastal bias to rainfall, but also the impact of that easterly shift along the east coast with low pressure rolling through the southern states. You can see the rainfall return for coastal NSW and the adjacent inland. This would see the dry season end for the east coast which is normal for this time of year.

12z CMC Rainfall for the coming 10 days

The CMC data supports moisture being drawn from the tropics next week bringing a broken band of showers and thunder through QLD and NT but mainly elevated with light falls. Frontal weather from WA through SA and into VIC taps into modest moisture to bring moderate rainfall for the southeast inland. But the east coast is expected to dry for the coming 10 days. Dry weather is expected right through the inland if this verifies.

12z KMA Rainfall for the coming 12 days

This is picking up more moisture being drawn in from the Indian Ocean rather than coming through the eastern inland via the NT. So this would see rainfall chances remain moderate to high through the outlook from Thursday onwards for southern Australia, possibly impacting areas of eastern NSW. The onshore winds are not as deep over QLD seeing less moisture drawn through northern Australia if this verifies.

18z ACCESS Rainfall for the coming 10 days

Rainfall is limited to the the southern coastal areas through the coming 10 days though the data is creeping that moisture further north next week through NSW west of the divide with a stronger system. The moisture also hangs back over parts of inland WA and western SA. The models are expected to increase over northern Australia in line with other models. The inland though suppressed under high pressure but it is only a matter of time to see the heat and moisture put to use with lower pressure.

So the moisture and areas of rainfall based upon all the data is the possible for the following areas highlighted in yellow. These areas as you know will move around as they should as the data moves - but it gives you a sense of trends and an idea of what all the data looks like. I have also drawn in the low pressure symbols as well to show you where the models are suggesting they will likely set up. The arrows show the two global models ensemble data sets and where the moisture is moving in relation to pressure patterns. Those areas in yellow are not guaranteed rainfall but likely to feel some impact in relation to moisture.


Moisture Watch Week 1

The moisture is limited to coastal areas over the south of the nation in line with the run of cold fronts and a modest amount of moisture drawn in from the Indian Ocean. This is leading to increased cloudy skies and areas of patchy rainfall moving from WA, through SA into VIC and more concentrated over western TAS. There may be a northwest in feed of moisture through the Pilbara ahead of the lead system mid to late this week. Onshore winds over the east will continue to bring moisture through the north of the nation and an increase in humidity is likely to be experienced over the north of the nation. That moisture will run over either WA or offshore WA next week, hence why it is now looking unlikely to be drawn into the long wave over the southern and eastern parts of the nation at this time. Some models do lift that moisture later in the period but it is a split camp and I am leaning to the moisture being out of phase for now.

Moisture Watch Week 2

This chart is presented to show you the current data sets and trends in the global model suite, the injection of drier air through the nation has increased for the final week of the month, but the east turns wetter according to the models with easterly winds developing and a low sitting offshore. Moisture also coming in on the northwest jet stream ahead of another low offshore WA with rainfall chances increasing there. Moisture being kicked off the north of the nation through the Torres Strait may return into September.

I will have another update on the medium term forecasting tomorrow, but it is not as easy to forecast at the moment with the pressure pattern shifting less zonal (west to east) and becoming more meridional (wavy flow more north to south).




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