January update 2025 SA

January update 2025 SA

*Forecast prepared between Jan 20th-24th 2025

Review:

G’Day one and all, I hope the summer period is treating you well with whatever you may be doing be it some well-earned rest, family time or on holiday. Myself, I am still recovering from the dreaded December lurgy 1 month on and whilst I feel better, the lungs certainly do not. Hopefully they do soon!

January so far has been quiet weather wise apart from some patchy light rain on both the 5th and 14th with the 5th producing the best totals, but most were under 5mm or so north of the SE Districts where 7-10mm did fall. These totals increased over the border into VIC and did assist in helping put out the Grampians fire. There have been some hot to very hot days but for the most part a lot of temperatures in the 28-35C range as ridges in the Bight keep a SE flow over the state with deep troughing over QLD, NSW and at times VIC. This SE flow is stable, warm to hot and very dry with only brief humid bursts pushing westwards to deliver afternoon convection at times about the ranges and eastern border districts. Overall, I think January will be drier than I initially expected by a small amount.

I should also mention the significant heat through WA of recent times and much more is set to occur into Feb. Geraldton Airport reached 49.3C on the 20th which equals its hottest temperature of all time. I think it will give this another crack if not beat it (50C or somewhere over there) with the next deep heat trough there in early February as the deep E/NE component across Central Australia will really drive the heat west right across coastal areas and that will include Perth for some mid to even high 40’s potentially if things line up – it is looking like a very hot period for WA so for those of you there, please take note.

Meteorological Discussion:

Currently as of the 20th we have Severe Tropical Cyclone Sean off the coast of Exmouth steadily moving SW. Feeder bands converging into the system from the NE have lashed Karratha with 274.4mm in 24hrs with wind gusts to 104km/hr and this was well away from the core but shows the power of convergence bands that do feed into the system. Aside from that, the worst winds which are gusting to 250km/hr will be well offshore and pose no threat. Sean will turn southwards and encounter increasing wind shear, cooling SST’s and begin to weaken below Tropical Cyclone strength on about the 23rd and largely unravel offshore before the remnants get captured in a shortwave trough and push eastwards with some areas of patchy rain for the SW tip of WA around the 24th/25th but very minimal rainfall.

The pattern after this will still remain relatively mobile. The heat expected late January and into Feb is going to come but in shorter bursts of extreme temperatures – plenty of low to mid 30’s and one or two days near or above 40C before dropping again.

Then slowly but surely, we will see a reduction in the fast moving weaker changes and a more broader inland troughing pattern with the easterly dip moving westward and a ridge pushing up the QLD coast (traditional Feb pattern) with increasing monsoonal and tropical cyclone activity or at least potential for the latter and a greater chance of infeeds from the NE to N as high pressure systems settle in below the mainland driving that flow towards us. This will increase heat (especially holding up the main oven over WA at first as touched on earlier) and moisture as we move through February and into March.

Back to SA though and from now till the end of January there really isn’t a great deal to talk about. Ridge will move eastwards allowing heat to come down especially for Australia Day followed by a trough and a cooler change on the 27th over western, southern and central areas. The east will be very hot with temperatures in the mid 40’s on the 27th before the change arrives. There also maybe a mid-level shower nudging up towards KI and perhaps a light sprinkle or two in the onshore SW-S flow with the new ridge behind through the overnight period into the 28th. After this the main feature will be an easterly dip type trough attempting to move west into SA and remain slow moving but more on that in the February outlook.

Climate Drivers:

The Pacific has been relatively stable in the last 2 weeks but the cooler anomalies that we see are resembling a La Nina Modoki style setup where they sit more in the middle of the Pacific rather than the east. Having said that whilst we are very close to La Nina by the numbers, the thresholds are still not being met and the connection to the atmosphere is only half-hearted right now. Trade winds are about average however rainfall has been fairly solid over the Eastern seaboard of Australia, especially SE QLD down to NSW. The Tropical Far North coast of QLD though is still struggling with the MJO not being favourable most of the time. I expect improvement through Feb and March there.

Figure 1: Current SST anomalies – source Tropical Tidbits https://www.tropicaltidbits.com/analysis/ocean/cdas-sflux_ssta_global_1.png

Now the Indian has really been active of late with the very much above average temperature waters persisting off the NW coast of WA. This is slowly creeping southwards down the coast and is very soon going to represent a more typical Ningaloo Nino type of pattern. Typically, these patterns assist in late autumn rainfall but for now there is minimal influence apart from the increased convection over these areas, largely attributing to the MJO approaching from the west and the current Tropical Cyclone Sean that has just formed. I see this area being active through the remainder of the Northern Australia Wet Season with cloud/convective activity and Tropical Cyclones. The IOD itself is irrelevant at this time of the year but moving through 2025, I can at least see a weak negative IOD forming and possible moving into moderate territory should we persist with such patterns, but I will have more confidence on the matter by later Feb and into March.

The MJO is approaching the mainland from NW with a large increase in tropical convection visible on satellite imagery. Tropical Cyclone Sean has formed off the Pilbara coastline and rapidly intensified to category 4 which is no surprise given the very warm SST’s there. A weak monsoon has developed across the top end only to retreat once the Cyclone dragged the flow more into it instead and because it was so short-lived, the onset was not officially counted. This now is likely to be the latest onset in history eclipsing 1972/1973 which came on Jan 25th. A secondary burst however is likely very late Jan and into early Feb as the MJO moves east across the top of Australia with an increase in rainfall also coming to tropical QLD which as mentioned above has been rather dry.

Possible Gulf of Carpentaria or Coral Sea Tropical Cyclone development can’t be ruled out either in the 10–14-day window most likely. I cannot see huge moisture infeeds from this pulse just yet, but an increase in heat is likely and we have already seen some of that now which was expected. A more set in stone heat low and upper ridge is needed first before copious amounts of tropical moisture flow inland and south where the blocking pattern stops the westerlies and coastal changes pushing moisture away which has been happening all summer now.

Finally, the SAM has shown a very steady tendency in the past 2-3 weeks with a neutral flavour, perhaps still slightly negative as the westerly belt continues to hinder any moisture coming into our region. February is usually the month where positive SAM is the most likely combined with the monsoon flow and maximum southward extent of high-pressure systems and deeper upper ridging. I expect that to come around with a more neutral to positive SAM in February, especially from about a week in.

Districts:

Given there is no rainfall to report I won’t include a detailed districts forecast as it is much of the same. As mentioned above, hot to very hot conditions Australia Day before that cooler change on 27th the main feature. Fresh seabreezes most afternoons will be a feature and evening gully winds about western slopes of the ranges, in particular the 28th-31st period although nothing too vigourous at this stage.

Final Notes

· Status quo across the state as dry weather largely dominates

· Increasing heat late Jan and more so generally through February together with slow moisture infeeds with extreme heat over WA pushing records

· More Tropical Cyclones and monsoonal lows to develop as we move forward through February-March

· Ningaloo Nino like pattern to persist through late summer and autumn before weakening

· Whilst better rainfall prospects this autumn than 2024, expect a drawn-out Indian Summer pattern again through April at least

· Weak to moderate negative IOD for 2025 with a neutral to cool neutral ENSO looks the most likely giving rise to closer to average rainfall at this stage

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Happy Farming and Cheers from The Weatherman

*Note – For interest only, all thoughts are of The Weatherman and may not be reproduced without my consent.