October outlook 2024 SA

  

*Forecast prepared between October 1^st-3rd 2024  

  

Review:  

G’Day one and all, October is now here and certainly a critical time in regard to how things finish. For some, there has been too much damage done and that is greatly unfortunate and sad to see. For others, there is still some hope left where a few mm here and there may end up giving the last finish for what is still growing, albeit at a very reduced yield. We’ll take a look at what we can find for the rest of this month and then going forward.

Firstly, though as usual, a look back at the month that was, or should we say – wasn't in September. The expectation many months out was that we’d be making a run at a Negative IOD with September showing improvement compared to July and even August with a building towards a better finish to the year. Fast forward to the start of September and it was clear that that was out the window with a much-revised forecast which I will put below:

“Overall, in terms of a September rainfall outlook I am expecting a mixed bag across the districts ranging from below average to above average. The greatest risks of above average are over the Lower SE, Kangaroo Island and potentially some parts of the outer NW and NE Pastorals. Activity will drop away to average to below average across most central areas, and down to generally below average for eastern Districts including the Upper SE, Mallee, Riverland. The Eyre Peninsula will be around average to slightly below at this stage but no strong signals either way. So an improvement on August but not by a great deal”

Taking a look below now at the relevant charts for September starting with the Deciles in Figure 1:

 

Figure 1: September 2024 rainfall deciles – source BoM http://www.bom.gov.au/climate/

Figure 2: September 2024 rainfall percentages – source BoM http://www.bom.gov.au/climate/

 

Figure 3: September 2024 rainfall anomalies – source BoM http://www.bom.gov.au/climate/

As we can see, most of those charts paint yet another grim picture for the agricultural areas which in the end was generally expected. The slightly higher chance of above average in the forecast of the Lower SE KI and NW Pastoral areas, mostly only occurred for the Pastoral area thanks to tropical infeeds but a slither of the Lower E coastline managed to get there thanks to being far south enough to get the top edge of weak fronts, which never had influence further north. But the bulk of the rest were very dry and if it were not for a reasonable rain event towards the end of the month with 8-15mm totals, we’d have seen a lot more of the lowest on record coloured in. All in all, another very poor month in the growing regions with any moisture completely halted beyond the NW corner of the state.

Now onto that rain event and there was an expectation of a more significant system around the 24^th-27^th or so from the mid-month forecast. The first attempt at a system resulted in a broad and waffly trigger with no focused convergence and poor connection to the tropics and as a result only very light patchy rain was recorded and mostly under 1mm. Fortunately whilst in that window, another front moved in and captured the moisture that failed to connect and we saw a better broken up series of rainbands from the mid-levels on the 28^th and early hours of the 29^th which generally saw most locations east of the Spencer Gulf receive 5mm or more. There were some good 15-30mm falls in the Mount. Lofty Ranges thanks to orographics but the main good news was falls of 5-10mm across the Mallee area and 8-14mm over the Upper SE. Very much welcome but in the grand scheme of things, a mere drop in the ocean and more is needed.

Overall, a poor month with significant frost early and a late rain only the saving grace.

Meteorological Discussion:

Onto current proceedings and we have a strong pre-frontal trough and cold front blasting across WA with a broad upper trough behind containing a lot of cold air. This is providing an ideal thermal gradient for severe weather to form along and ahead of. The system has already given good falls over WA with severe thunderstorms to boot, tapping into some moisture lingering over inland WA. The downside is the entire system will dry out and weaken as it moves through SA (a standard affair for us unfortunately). Nevertheless, we will see some activity so let's look at what to expect with it as it moves across.

A broad area of mid to upper-level cloud is crossing SA generating areas of patchy light rain. Ahead of this unfortunately, fresh to strong and very dry northerly winds are funnelling south ahead of the system adding more curing to already stressed crops. The patchy light rain will weaken out as it crossed the gulf area with no sustaining uplift to keep it going since it was merely the remnants of strong thunderstorm activity over WA yesterday. Further west, a cold front is marked by a line of heavier showers and thunderstorms is moving quickly eastwards however most of the thunderstorm activity will weaken into a slightly thicker band of rain catching up to the decaying one ahead. Another weak trough is located just west of the front with some isolated showers and thunderstorms. All this will extend E/SE across the agricultural and adjacent pastoral areas on the evening of the 3^rd and early hours of the 4^th for the eastern districts. Generally light falls are expected although with western extent, some totals may be useful enough across the western and southern/Lower Eye Peninsula up to about 10-12mm potentially. Further east away from the lift of the ranges, most totals will come in around 1-5mm, perhaps some isolated 6-7mm luckier totals.

General scattered mid-level showers and isolated thunderstorms will clear the E/SE of the state by sunrise as a low moves in from the west south of the state with onshore shower activity. Aloft an upper trough will result in showers increasing with some daytime heating during the 4^th before clearing again during the evening. Another cold front in the onshore flow will move in from the WSW reaching Kangaroo Island just after 12am on the 5^th with a band of showers. These will arrive in the Adelaide area by about sunrise with showers then extending across much of the southern agricultural area, more frequent about the ranges. Given the timing, there should be reasonable penetration across the Mallee this time around with the band moving through, although isolated towards the Riverland. I suspect this band will give better totals than the activity the night before for nearly all areas east of the ranges. Falls will still be light but perhaps 1-4mm from the shower activity is a reasonable expectation with some 5-6mm localised totals possible closer to the Upper SE and more over the Lower SE.

On the 6^th still embedded in a moist onshore WSW flow another weak front will clip the SE of the state – weaker than the one the day prior but enough to bring another broken band of showers to chiefly the SE Districts and the southern coasts and ranges including KI.  A repeat will occur again on the 7^th, a weak sliding front clipping the Lower SE.

A clearance will occur ahead of a weakening front from WA with a decaying band of mid-level showers around the 10^th but don’t expect much here. Beyond this high pressure will temporarily take hold ahead of some trough activity deepening out of inland WA towards mid-month but it is too early to tell if this will connect with any colder air out of the SW.

Overall, my outlook for October is for average to slight below average rainfall across most agricultural districts. The greatest chance of average rainfall or slightly above again is the Lower SE which like September will just be south enough to receive fronts. The greatest chance of above average again will be the western border areas up to about Western Eyre Peninsula but moreso into the NW corner of the state.

 

Climate Drivers:  

Now the Pacific has seen a stall in any movement towards La Nina which November and December really the final window to get one declared. It may be a case of NOAA declaring but the BoM not it is that much of a knife edge and in that case a cool neutral will be the final call for 2024 by the BoM. There is still cooler water to upwell but not a great deal, the Humboldt Current remains steady with no changes. Trades have dropped back to near average again so despite a good burst, the final levels have not been reached. In any case, a good amount of warmer water remains to the north of PNG and generally NE of Australia (see Figure 4).

Figure 4: Current SST anomalies – source Tropical Tidbits https://www.tropicaltidbits.com/analysis/ocean/cdas-sflux_ssta_global_1.png

The Indian unlike the Pacific has continued its trend towards a negative IOD, the ever pulsing and flipping values that have plagued the 2024 season so far. As expected through spring, we are now dropping with the latest value coming in at –0.39C at the start of October, a hairs breath away from negative values once again. This time I expect those values to hold around –0.4C maybe even lower before moving back to neutral. I don’t quite think we hold there long enough to make it officially negative but like it has done on both the positive and negative side earlier this year, hold for a few weeks then shoot back the other way except this is the last move in the IOD window which closes once the monsoon season approaches, destroying the surface wind patterns that generate the anomalies we see. This will increase moisture feeding into the NW of Australia through spring, but chiefly November and December. It won’t be huge but an improvement from what we have seen. The key for me is getting heat in first, once we get heat in then the moisture will have a much easier path into those troughs. Trouble is, that will be harvest time for those that do have something to reap or hay bailing time. Frustrating but I am sure anything will be taken.

Now moving onto the SAM, we have a decent dip into the negatives which is at least getting some fronts into the area but not too strong like late August to early September so at least it is allowing some WSW flow with onshore flow but not strong enough to make it a flat westerly flow with big wind which does nothing to help the situation rainfall wise. The SAM is expected to move back to neutral ground as we nudge through October but perhaps with a negative flavour lingering aloft as I can see a lot of meandering of the jetstreams thanks to some very strong solar activity from the sun in the last few days so watch this space for some ‘random’ or unorthodox systems.

The MJO is currently on the other side of the world around the African region at a moderate strength. It is expected to move towards the Australian region by mid-month at a similar strength but may lose steam once it moves into the Pacific. Look for increased tropical thunderstorm activity by mid-month. This will be well timed to enhance any potential negative IOD influence albeit a shortened one.

Districts:    

Eyre Peninsula  

Trough and cold front will combine to generate areas of patchy rain during the afternoon and evening of the 3^rd with a line of showers and isolated thunderstorms to follow, gradually tending to areas of rain over the Lower Eyre Peninsula. Weak upper trough on 4^th with scattered showers. Cold front early 5^th with a band of showers, becoming much more isolated towards the NE corner of the Peninsula. Another weaker front clipping the coast on the 6^th with isolated light showers in the far south followed by a repeat third weak front on the 7^th with similar conditions. Remaining mostly fine further north. Weak trough around 10^th though generally remaining dry. Increasing instability likely through the mid-month period from 13^th-19^th or so with a couple of potential stronger systems with showers and thunderstorms extending from the NW. Rainfall for the period 5-12mm generally, increasing to 12-18mm about Lower to Western coastal Eyre Peninsula. Totals decreasing towards the N/NE corner down to 3-5mm.

Upper North  

Trough and cold front will combine to generate areas of patchy light rain during the late afternoon and evening of the 3^rd with isolated showers and thunderstorms to follow, more likely with southern extent. Weak upper trough on 4^th with isolated showers. Cold front on 5^th with a band of showers, becoming much more isolated towards the back side of the ranges and north of Port Pirie. Another weaker front clipping the coast on the 6^th with isolated light showers in the far south followed by a repeat third weak front on the 7^th however no rainfall is expected. Weak trough around 10^th though generally remaining dry apart from a possible mid-level shower. Increasing instability likely through the mid-month period from 13^th-19^th or so with a couple of potential stronger systems with showers and thunderstorms extending from the NW. Rainfall for the period 2-4mm generally, increasing to 5mm about elevated terrain in the south. Totals decreasing towards the back side of the ranges and the Flinders down to 1mm or so.

Lower North  

Trough and cold front will combine to generate areas of patchy light rain during the late afternoon and evening of the 3^rd with isolated showers and thunderstorms to follow, more likely with southern extent. Weak upper trough on 4^th with isolated to scattered showers. Cold front on 5^th with a band of showers, becoming much more isolated towards the back side of the ranges and the northern portions of the district. Another weaker front clipping the coast on the 6^th with isolated light showers followed by a repeat third weak front on the 7^th with further light showers only in the south. Weak trough around 10^th though generally remaining dry apart from a possible mid-level shower. Increasing instability likely through the mid-month period from 13^th-19^th or so with a couple of potential stronger systems with showers and thunderstorms extending from the NW. Rainfall for the period 3-6mm generally, increasing to 8mm about elevated terrain in the south. Totals decreasing towards the back side of the ranges down to 1-3mm or so.

Yorke Peninsula  

Trough and cold front will combine to generate areas of patchy rain during the late afternoon and evening of the 3^rd with isolated showers and thunderstorms to follow, with rain more likely down the lower half of the Peninsula with thunderstorm activity more likely to the north. Weak upper trough on 4^th with isolated to scattered showers. Cold front early 5^th with a band of showers. Another weaker front clipping the coast on the 6^th with isolated light showers followed by a repeat third weak front on the 7^th with further light showers only about the foot. Weak trough around 10^th though generally remaining dry apart from a possible mid-level shower. Increasing instability likely through the mid-month period from 13^th-19^th or so with a couple of potential stronger systems with showers and thunderstorms extending from the NW. Rainfall for the period 5-10mm generally, increasing to 10-18mm about the foot. Totals decreasing towards the far north around 3-5mm.

Kangaroo Island  

Trough and cold front will combine to generate areas of patchy rain during the late afternoon and evening of the 3^rd tending to areas of rain at times. Possible thunder. Weak upper trough on 4^th with isolated to scattered showers. Cold front early 5^th with a band of showers. Another weaker front clipping the coast on the 6^th with isolated light showers followed by a repeat third weak front on the 7^th with further light showers. Weak trough around 10^th though generally remaining dry apart from a possible mid-level shower. Increasing instability likely through the mid-month period from 13^th-19^th or so with a couple of potential stronger systems with showers and thunderstorms extending from the NW. Rainfall for the period 8-15mm generally, increasing to 15-25mm about the western end. Totals decreasing towards the eastern end down to around 7-8mm.

Adelaide Plains  

Trough and cold front will combine to generate areas of patchy rain during the late afternoon and evening of the 3^rd with isolated showers and thunderstorms to follow. Weak upper trough on 4^th with isolated to scattered showers. Cold front early 5^th with a band of showers. Another weaker front clipping the coast on the 6^th with isolated light showers followed by a repeat third weak front on the 7^th with further light showers only about the outer southern suburbs. Weak trough around 10^th though generally remaining dry apart from a possible mid-level shower. Increasing instability likely through the mid-month period from 13^th-19^th or so with a couple of potential stronger systems with showers and thunderstorms extending from the NW. Rainfall for the period 5-10mm generally, increasing to 10-15mm about the foothills and southern suburbs. Totals decreasing towards the outer northern plains down to around 3-5mm.

Mt.Lofty Ranges 

Trough and cold front will combine to generate areas of patchy rain during the late afternoon and evening of the 3^rd with isolated showers and thunderstorms to follow. Weak upper trough on 4^th with isolated to scattered showers. Cold front early 5^th with a band of showers, with showers more frequent and heavier over the southern Fleurieu. Another weaker front clipping the coast on the 6^th with isolated light showers followed by a repeat third weak front on the 7^th with further light showers, chiefly about the southern coasts and ranges. Weak trough around 10^th though generally remaining dry apart from a possible mid-level shower. Increasing instability likely through the mid-month period from 13^th-19^th or so with a couple of potential stronger systems with showers and thunderstorms extending from the NW. Rainfall for the period 5-12mm generally, increasing to 12-18mm about the southern Fleurieu. Totals decreasing towards the northern ranges and in the lee side down to around 3-5mm.

Riverland/Mallee  

Trough and cold front will combine to generate areas of patchy light rain during the evening of the 3^rd and into the early 4^th with isolated showers and thunderstorms to follow, more likely with southern extent across the Mallee. Weak upper trough on 4^th with isolated showers again more likely over the southern Mallee. Cold front on 5^th with a band of showers, becoming isolated over the Riverland. Another weaker front clipping the coast on the 6^th with isolated light showers in the far southern Mallee followed by a repeat third weak front on the 7^th however no rainfall is expected. Weak trough around 10^th though generally remaining dry apart from a possible mid-level shower. Increasing instability likely through the mid-month period from 13^th-19^th or so with a couple of potential stronger systems with showers and thunderstorms extending from the NW. Rainfall for the period 3-5mm generally, increasing to 5-8mm about the SW/S Mallee. Totals decreasing towards the Riverland with 1-3mm expected there.

Upper SE  

Trough and cold front will combine to generate areas of patchy light rain during the evening of the 3^rd and into early 4^th with isolated showers and thunderstorms to follow, chiefly towards the north. Weak upper trough on 4^th with isolated showers. Cold front on 5^th with a band of showers. Another weaker front clipping the coast on the 6^th with isolated showers followed by a repeat third weak front on the 7^th with further isolated shower activity. Weak trough around 10^th though generally remaining dry apart from a possible mid-level shower. Increasing instability likely through the mid-month period from 13^th-19^th or so with a couple of potential stronger systems with showers and thunderstorms extending from the NW. Rainfall for the period 8-12mm generally, increasing to 12-15mm in the far south. Totals decreasing towards the Mallee with 5-8mm expected there.

Lower SE  

Trough and cold front will combine to generate areas of patchy rain during the evening of the 3^rd and into early 4^th with isolated showers and possible thunderstorms to follow, chiefly towards the north. Weak upper trough on 4^th with isolated showers. Cold front on 5^th with a band of showers, potentially heavy at times. Another weaker front clipping the coast on the 6^th with another band of slightly lighter showers followed by a repeat third weak front on the 7^th with further showery periods within the frontal zone. Weak trough around 10^th though generally remaining dry apart from a possible mid-level shower. Increasing instability likely through the mid-month period from 13^th-19^th or so with a couple of potential stronger systems with showers and thunderstorms extending from the NW. Rainfall for the period 15-25mm generally, increasing to 25-30mm towards the southern coastline. Totals decreasing towards the Upper SE with 12-15mm expected there.

Western VIC  

Trough and cold front will combine to generate areas of patchy rain during the late evening of the 3^rd and into early 4^th with isolated showers and possible thunderstorms to follow, chiefly towards the Mallee. Weak upper trough on 4^th with isolated showers, with possible thunderstorms in the east of the SW District. Cold front on 5^th with a band of showers, potentially heavy at times in the afternoon over the SW District and southern Wimmera. Another weaker front clipping the coast on the 6^th with another band of showers followed by a repeat third weak front on the 7^th with further showery periods within the frontal zone. All activity struggling to reach past the Wimmera District. Weak trough around 10^th though generally remaining dry apart from a possible mid-level shower. Increasing instability likely through the mid-month period from 13^th-19^th or so with a couple of potential stronger systems with showers and thunderstorms extending from the NW. Rainfall for the period 15-25mm generally about the SW District increasing to 25-35mm towards the southern coastline of the SW District. Totals decreasing towards the Wimmera with 5-12mm and then less again for the Mallee with 3-5mm expected there.

 

Final Notes  

·         A few weak fronts and troughs to keep some totals ticking over, but more is needed

·         October will be what I call a lead in month with improvements to heat and troughing, but moisture won’t properly come down till November and December with increased shower and thunderstorm activity, but with a mid-level flavour

·         Brief negative IOD attempt for November, otherwise on the negative side of neutral

·         Weak La Nina attempt but otherwise on the cool side of neutral

·         Above average wet season likely for ther tropics and adjacent inland

·         Summer rainfall and temperatures in SA looking very close to the mean at this stage

  

Link to temporary blog website: https://farmweathersa.blogspot.com/  

  

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.