Updated: May 25

Lets get to the Indian Ocean first before we look at the 2 week outlook with rainfall.

The weather is very much of low confidence as we have seen quite a variety of outcomes but this is where things stand on the latest data sets.


Sea Surface Temperatures Anomalies.

During the past week there has been some modest warming of the basin, but with dry air aloft through the region, blowing off the continent, which is seasonal for this time of year, there has been little cloud cover. The solar hours warming the basin will continue to support the basin warming over the coming week but upwelling is still occurring and further warming is likely in the coming weeks. The warming has not been as aggressive as some models have suggested.

18Z GFS Precipitable Water Values next 16 days - Indian Ocean

The PW values are showing the pattern flip I was talking about at the end of July, the drier air over the southern latitudes in line with the westerly belt relaxing. There are fronts through the Indian Ocean and you can track the movement of them, however they are further south than the previous 8 weeks. You can note that with the lack of deeper moisture being pulled south, allowing for drier air to rush into the southern parts of the basin. By the end of the period you can see the moisture being drawn south and southeast as a broad upper low comes into the Central Indian Ocean, that could be the catalyst for why there is such a wet signal for the end of August and to kick off September, but again its an idea on the table that may explain these wetter signals in the coming weeks.

18Z GFS Precipitable Water Anomalies next 16 days - Indian Ocean

The anomalies are not running that high through the coming week, with a lot of the basin seeing that drier air just taking over. But once the monsoon over the sub continent returns, we may start to see the moisture move south and southeast through the Central Indian Ocean towards the 20th of August at the earliest and then transport southeast and east.

18Z GFS Upper Level Winds at 18000ft next 16 days - Indian Ocean

The wind profile is really important up above our heads. You can see the mid latitude westerly winds with the waves passing through moving further away from Africa and Australia during the period and then once that occurs, it allows there to be more mixing of the atmosphere, seeing low pressure form. This is an example of the importance of the low pressure systems that form out to the west of the nation as the upper level northwest winds develop. This draws the moisture from the northwest to the southeast with that moisture then lifted into areas of rain for Australia. That setup you can see at the end of the period offshore WA is classic for bringing the wetter weather in via the Indian Ocean. I would like to see the area south of Indonesia to wake up a bit more as well and the upper high pressure to move.

18Z GFS Rainfall for the next 16 days - Indian Ocean

Rainfall is very heavy and highly anomalous for parts of the Northern Indian Ocean, that is thanks to the monsoon further north but the moisture has been bias further south this year. The moisture will eventually be pulled south through the Basin but more likely towards the end of the month and into September, hence why we are seeing those elevated signals for below average temperatures over inland areas of the nation and higher rainfall chances. The rainfall signal for August has also been running above average for many areas and it may be related to the last 10 days of the month. We wait and see.

18Z GFS Rainfall Anomalies for the next 16 days - Indian Ocean

You can clearly see the 100-200mm anomalies over the northern basin heading south and then part of that moisture being drawn southeast as the upper level winds turn northwest through that region propelling the moisture towards WA. The last time we saw these elevated levels was back in June and the west of the nation was exceptionally wet and it lead to a wetter than average June and July for large parts of the east, but the lag impact was about 7 days after the period. So if this is correct you would be looking at the last week of the month being wet and cooler across large areas of the nation.

Euro 12z - Simulated Satellite Imagery next 10 days - Indian Ocean

The next 10 days shows the impact of dry air and sinking air motion with high pressure through the Basin, so for rainfall across the nation, we will have to rely on frontal weather and residual moisture being pumped in from the north and northeast via the easterly wind profile. But the moisture does start to increase from later next week which is in line with GFS.


Moisture Watch Week 1

Moisture is clearing out from west to east today with the front passing through this afternoon over SA and then VIC and NSW tonight. Some of that moisture becomes stagnant over the northeast of NSW and southeast QLD this weekend, I will reassess the impact of that tomorrow with new data as I may expand the area of impact further west. The east coast to see the most of the moisture during this week with easterly winds, likely to run over the northern parts of the NT and possibly into the north of WA at this time next week, but more likely afterwards. Moisture offshore WA being propelled west and away from the coast with the east or northeast winds. But that moisture may turn towards the coast in the second week.

Moisture Watch Week 2

The moisture offshore WA is likely to turn back towards the coast during the 20-24th of August on current projections, rainfall may develop if frontal weather captures the moisture or a trough is nearby. Moisture over the tropics may be drawn southeast into frontal weather coming through the southern ocean with a widespread rainfall event possible from the 20-23rd of August. Moisture persisting over the eastern inland of QLD and northern NSW may bring showers inland through mid to late next week.

That means the rainfall is very much hard to pin down with a broad area analysed through the period.

Rainfall for the coming 16 days - LOW CONFIDENCE FORECAST

Rainfall is expected to increase for the second half of the month with easterly winds returning with showers increasing for the eastern coast. The moisture over the northern parts of the NT may trigger showers and storms. The moisture will also return to the northwest of Australia but may be drawn south through WA with a cold front approaching. The highest chance of rainfall in the coming period would be the moisture streaming from northern Australia into the southeastern inland with moderate falls developing as that event unfolds later next week. That has been been the most consistent feature across the models. With all the ingredients in play, it is just a matter of them all coming together and there is a chance that could happen in this period, but there is no skill in telling you when that will happen when the guidance is so poor.

More to come.

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