November update 2023 SA
November update 2023 SA
*Forecast prepared between November 15th-17th 2023
Review:
G’Day everyone, I hope you are keeping well as we move to the halfway point of November, a busy time for many I am sure with the harvest. I hope for those that do receive this that your frost damage is not too bad, but I understand there are some areas that have not fared too well. I truly hope your 2024 is a much kinder one – I think it should be rainfall and frost-wise.
So far this month we haven’t seen a great deal of active weather with a relatively settled and stable pattern across the state. Heat has made a couple of moves south however ahead of a trough, the main one on the 10th where Adelaide came very close to the hottest ever day this early in the season with 40.3C (it needed to beat 40.4C). Many other areas across the Pastorals and agricultural areas moved into the 41-44C range with 44.3C at Tarcoola, 44.2C at Kyancutta & Whyalla, 44.1C at Port Augusta and 44C at Woomera.
Rainfall has been paltry to date with only some patchy mid-level rain from a weak trough late on the 13th where most totals were less than 1-2mm. See Figure 1 for current rainfall percentages:
Meteorological Discussion:
The current pattern has certainly shifted from the one we have seen from earlier in the spring where we saw a lot more westerly activity, but weaker fronts followed by strong highs. Right now we are seeing those highs sink further south but the net result is we still have those dry conditions so no matter where they go, we are battling for rainfall and that is due to the strength of these highs and ridges and the ease at which they can punch across our state, even amongst a lot of low pressure troughing inland and both east and west, that ridge is always finding a way to stick it’s nose in across SA, keeping us for the most part, at least over the agricultural areas fairly stable and dry. Now the strength of these ridges and highs is still tied into the broader El Nino and Positive IOD however with one weakening and the other already showing signs of doing so soon, things are about to change towards the wetter side of the spectrum.
The Easterly dip (trough that sits over Eastern Australia in the warmer months) will have more high pressure sitting under it than normal and what usually happens with this is it steers the trough inland a little and allows ridging up the QLD coastline (quidge as it is known to some). With the trough holding further inland to the west, this allows more showers and thunderstorms to develop across these inland areas with a slightly greater chance of that moisture feeding back into SA from the east and NE causing those days where you get the classic afternoon build-up from surface heating before going quiet again in the evening and this activity typically hugs the ranges however when the trough is closer or stronger and steering winds are not close to parallel to the ranges, these can form almost anywhere.
With that being said the coming couple of weeks are going to be very wet across QLD and NSW, especially S Central to SE QLD and Central and N to NE NSW as a result of that quasi-stationary trough where the moisture coming in from the NE is not cleared out by big westerly pushes, it simply keeps building up with that firm ridge keeping the NE flow angled into the trough. Aloft, multiple rounds of weak to moderate strength upper troughs will continue to pinch off from the westerly belt due to the blocking from the high pressure. When we have a locked In or blocked pattern, we typically see more wandering upper troughs and some of these become cut off into upper lows. These upper troughs and or upper lows essentially turbocharge the surface troughs to assist in more widespread and heavier showers, thunderstorms and rain areas and this will lead to some minor to moderate flooding at times although the area has been extremely dry until this point so a lot will soak up into the ground. It will certainly change things from drought or near drought though to quite damp fairly quickly, but this is expected as we move through the summer period where more areas will see this sort of rainfall and activity as moisture builds into 2024.
Just quickly, WA has seen quite a bit of thunderstorm activity lately as the WA heat trough fires up. With the highs planted well south, some cold air aloft has been present which has assisted in some severe thunderstorms and a couple of left moving supercells with vast quantities of hail smashed the Hyden area which was extremely unfortunate. Isolated but very intense at the same time. Apart from this, for the most part it looks relatively dry and stable there for the remainder of the month.
Now back to SA and currently we have quite a contrasting pattern over the state. In the south we are under the influence of what seems like a never-ending ridge of high pressure which keeps planting well below the Bight extending a stable S-SE airstream across the south. As the high tries to move east these winds turn a bit more SE-E but this then gets compressed by the deepening easterly dip to the east. This pattern has been and will continue to oscillate back and forth with occasional stronger pulses of SE winds causing fresh to strong seabreezes and gully winds at night about western slopes of the ranges. This pattern is fairly common in February and March as opposed to November where there is usually a bit more frontal action from the west. A weak El Nino and weakening Positive IOD can commonly cause very strong highs right through spring and by November these are usually beginning to shift south and thus we see more SE winds than usual, especially with the Positive SAM (will touch on this more in the next section). The net result is what seems like a never-ending pattern of dry, SE winds for the most part and this is expected to continue for another week or so before the increasing influences of moisture from the tropics and Eastern Australia filter further South/SW.
However inland things are quite different. Not only has it been very hot with multiple days (over a week in some areas) over 40C but instability and moisture has increased ahead of a broad trough across the N and NW. Together with some help from a weak upper low centred over the west of the state we have seen widespread showers and thunderstorms across the West, NW, N and NE portions of the state. Due to the strong wind shear aloft as well as low level turning, some of these thunderstorms are easily making severe levels with destructive winds, large to giant hail and intense rainfall with these storms traversing over vast distances due to their organisation into Mesoscale Convective Systems. As I type this on the 17th, we have already had 2 days of this severe activity and there will be another 2 days of this including this afternoon.
Beyond this we will see the upper low weaken although some isolated mid-level showers and thunderstorms are likely near it across the Southern NW Pastoral, Nothern Eyre Peninsula and possibly the Flinders District on the 17th and 18th. A strong high-pressure ridge holding well south of the mainland and an easterly dip trough anchored across NSW/QLD and into VIC will maintain moderate to fresh SE winds and afternoon sea breezes.
The high-pressure ridge will hold firm in the Bight directing that stable SE flow across the state however aloft an upper trough is likely to pinch off from the westerly belt and roll up to the NE. This will increase the showers and thunderstorms over NSW and QLD before the easterly dip slowly begins to push back west. It will meet stiff resistance with this high but some afternoon buildup is possible in the NE Pastoral and Riverland from the 21st with perhaps a couple of isolated showers. VIC may see some isolated afternoon showers and thunderstorms potentially on the 21st subject to how well this trough deepens and shifts west.
Further towards the last week of the month the chances of shower and thunderstorm activity working down into the agricultural areas increases as the pattern allows the ridge and high to shift east. Fresh to strong SE winds may especially be a feature as the main centre of the high pushes east at the same time the easterly dip trough tries to come west tightening the pressure gradient. Gully winds are likely to enhance during this period which is roughly between the 22nd and 27th. I’d suspect the first day of an increased chance in shower and thunderstorm activity filtering into the agricultural areas (eastern) is around the 24th or so although there could be afternoon build up each day from the 21st in the NE Pastoral. I expect a weakening of the high and shift east allowing the inland trough to deepen thanks to an upper low aloft pulling it closer and spread south allowing showers and thunderstorms to also affect more districts towards the very end of the month and possibly early December. A trough should then also extend from the west with a possible linking of the two before another ridge comes in and clears it all away. I’ll add a special update for this activity most likely as we get closer to the days. There certainly is the potential with these thunderstorms for some locally heavy but very sporadic falls as is the case when the moisture is sourced out of the NE. Given this, some locations are likely to rapidly go from well below average rainfall to above average from a single a single storm.
Climate Drivers:
The Pacific has essentially not changed in the last 2 weeks and even showed signs of some weak trades winds making an attempt to strengthen in the Western Pacific. This is linked in with the recent sustained Positive SAM causing more easterlies closer to the Australia Eastern coastline helping push moisture into the country from the Pacific and Tasman Sea. Historically, this won’t happen in stronger EL Nino’s but in weak ones, it can happen with relative ease and that is what we have atm. There is still warmer water in the Nino 3.4 region, so I still think a peak around early December for El Nino in terms of numbers however the actual on ground impacts are not likely to change a great deal more so what you see or have seen is what you get. After this we break down steadily through the summer months but there is a lot of warming of waters to be done around the Coral Sea and Top End of Australia to get SST’s back to standard numbers before we should see above average SST’s once again.
The Indian is showing clear moves now to a weakening Positive IOD and this is about when the stronger ones weaken off with the latest value coming in at +1.55C which is down from the peak near +1.85C. This should continue towards neutral values, and I expect those to be reached by Christmas with the rapid warming of the waters across much of the eastern Indian basin including across the Top End. The lag effect however between the ocean to atmosphere will linger a little longer but we should see more moisture moving in from the NW as we move into next year and certainly by autumn. Most of our moisture atm is coming from the Pacific Ocean/Tasman Sea in varying ways, be it directly off the ocean itself or from moving west across the top of the country before being fed into the mainland from there.
Figure 2: Current SST anomalies – source Tropical Tidbits https://www.tropicaltidbits.com/analysis/ocean/cdas-sflux_ssta_global_1.png
The MJO is still fairly weak and really is struggling to have any impact on our weather across tropical Australia and as a result, a lacklustre start to the build-up has occurred. Thunderstorms have been forming with the expected uptick from the 6th however many dry periods have continued to hamper stronger and deeper convection and with feeble MJO passes, this is not helping. We have a weak MJO over the Western Pacific atm and this is trying to shift east but overall, the pattern is not that strong right now.
Now the SAM has been positive for a while, and this looks to continue with a double down on strong positive values. This is not your typical SAM in November by any means, although in weak El Nino’s I have noticed this before where the highs get a long way south rather than sit that little bit north. Expect a lot of SE winds across the state, occasionally strong with the tight gradients to inland troughs causing gully winds to be strong at times in the coming weeks. With such a pattern we will see more moisture pour into the continent from both the E and the NE but a lack of significant triggers out of the west to date has kept things dry in our state. This is slowly eroding, little bit by little bit where weak upper troughs and cold air aloft moving across slowly increasing moisture in the lower levels is promoting instability and thus, we should see an increase in thunderstorms through the last part of November and also December. This has already started as per the discussion above with some active thunderstorms across the interior.
Districts:
****The complexity of the pattern ahead is likely to cause some wide variance in final rainfall totals due to the convective nature and position of the surface trough. A shift further west in this trough will greatly increase rainfall totals as well as their western spread. Special update to likely be released closer to event to get more accurate idea.
Eyre Peninsula
Weak upper low to west generating possible isolated showers and thunderstorms in the far north of the district on 17th and 18th otherwise fine. Firm ridge with moderate to fresh S-SE winds and seabreezes across the remainder from 19th through till 27th. Upper low aloft and westward moving trough from the east potentially causing isolated afternoon and evening showers and thunderstorms about the N and NE from the 25th. Locally heavy falls in some thunderstorms with possible hail. Another trough extending from west end of month to possibly link with first trough with increasing
heat ahead before a cooler change with new ridge contracts any shower and thunderstorm activity. Rainfall for period 5-15mm with isolated 20-25mm falls from thunderstorms. If trough shifts further west, then rainfall will likely double.
Upper North
Weak upper low to west generating possible isolated showers and thunderstorms in N Flinders on 17th and 18th otherwise remaining generally fine. Firm ridge to south with moderate to fresh S to SE winds with fresh seabreezes near the Spencer Gulf through the 19th-27th. Fresh gully winds at times, especially from 22nd to 27th approx. with tight SE gradient. Westward moving trough combining with upper low from about 24th to generate isolated to scattered afternoon and evening showers and thunderstorms. Locally heavy falls in thunderstorms, chiefly near the ranges as well as hail in stronger cores. Another trough may extend from west later in period with heat developing ahead before cooler air and a new ridge moves in contracting shower and thunderstorm activity eastwards. Rainfall for period widely ranging from 5-30mm. Isolated falls in thunderstorms to 50mm. If trough shifts west, then bottom end rainfall totals likely increase to 15-20mm.
Lower North
Weak upper low to west generating possible isolated showers and thunderstorms in N Flinders on 17th and 18th otherwise remaining generally fine. Firm ridge to south with moderate to fresh S to SE winds with fresh seabreezes near the Spencer Gulf through the 19th-27th. Fresh gully winds at times, especially from 22nd to 27th approx. with tight SE gradient. Westward moving trough combining with upper low from about 24th to generate isolated to possibly scattered afternoon and evening showers and thunderstorms. Locally heavy falls in thunderstorms, chiefly near the ranges as well as hail in stronger cores. Another trough may extend from west later in period with heat developing ahead before cooler air and a new ridge moves in contracting shower and thunderstorm activity eastwards. Rainfall for period widely ranging from 5-25mm. Isolated falls in thunderstorms to 40mm. If trough shifts west, then bottom end rainfall totals likely increase to 15-20mm.
Yorke Peninsula
Weak upper low to west on 17th and 18th but remaining generally fine apart from some high cloud. Firm ridge with moderate to fresh S-SE winds and seabreezes across the remainder from 19th through till 27th. Upper low aloft and westward moving trough from the east potentially causing isolated afternoon and evening showers and thunderstorms about the N portions from the 25th.
Locally heavy falls in some thunderstorms with possible hail. Another trough extending from west end of month to possibly link with first trough with increasing heat ahead before a cooler change with new ridge contracts any shower and thunderstorm activity eastwards. Rainfall for period 5-15mm with isolated 20-25mm falls from thunderstorms. Totals decreasing towards the foot to less than 5mm. If trough shifts further west, then rainfall will likely double.
Kangaroo Island
Weak upper low to west on 18th but remaining generally fine apart from some high cloud. Firm ridge with moderate to fresh (possibly strong at times) S-SE winds and seabreezes across the remainder from 19th through till 27th. Upper low aloft and westward moving trough from the east potentially causing isolated afternoon and evening showers and perhaps a thunderstorm should seabreeze convergence align though remaining fine for the most part. Another trough extending from west end of month to possibly link with first trough with increasing heat ahead before a cooler change with new ridge contracts any shower and thunderstorm activity eastwards Rainfall for period less than 5mm though possible totals to 10mm if a thunderstorm develops. If trough shifts further west, then totals likely at least double.
Adelaide Plains
Weak upper low to west generating high cloud on 18th otherwise remaining generally fine. Firm ridge to south with moderate to fresh S to SE winds with fresh seabreezes near the St Vincent Gulf through the 19th-27th. Fresh gully winds at times, especially from 22nd to 27th approx. with tight SE gradient. Westward moving trough combining with upper low from about 24th to generate isolated afternoon and evening showers and thunderstorms about the outer northern plains initially but likely extending southwards later in the period. Locally heavy falls in thunderstorms with possible hail in stronger cores. Another trough may extend from west later in period with heat developing ahead before cooler air and a new ridge moves in contracting shower and thunderstorm activity eastwards. Rainfall for period widely ranging from 5-20mm. Isolated falls in thunderstorms to 30mm. If trough shifts west, then bottom end rainfall totals likely increase to 15-20mm.
Mt.Lofty Ranges
Weak upper low to west generating high cloud on 18th otherwise remaining generally fine. Firm ridge to south with moderate to fresh S to SE winds with fresh seabreezes from Encounter Bay and the Coorong seabreeze through the 19th-27th with tight SE gradient. Westward moving trough combining with upper low from about 24th to generate isolated afternoon and evening showers and thunderstorms about the northern ranges initially but potentially extending south later in the period. Locally heavy falls in thunderstorms with possible hail in stronger cores. Another trough may extend from west later in period with heat developing ahead before cooler air and a new ridge moves in contracting shower and thunderstorm activity eastwards. Rainfall for period widely ranging from 5-20mm. Isolated falls in thunderstorms to 30-35mm. If trough shifts west, then bottom end rainfall totals likely increase to 15-20mm.
Riverland/Mallee
Weak upper low to west generating some high cloud on 18th otherwise remaining mostly fine. Firm ridge to south with moderate to fresh S to SE winds with fresh seabreezes near the SW Mallee and lakes through the 19th-27th. Westward moving trough combining with upper low from about 24th to generate isolated to scattered afternoon and evening showers and thunderstorms. Locally heavy falls in thunderstorms, as well as hail in stronger cores. Another trough may extend from west later in period with heat developing ahead before cooler air and a new ridge moves in contracting shower and thunderstorm activity eastwards. Rainfall for period widely ranging from 5-30mm. Isolated falls in thunderstorms to 50mm. If trough shifts west, then bottom end rainfall totals likely increase to 15-25mm.
Upper SE
Weak upper low to west generating some high cloud on 18th otherwise remaining mostly fine. Firm ridge to south with moderate to fresh S to SE winds with fresh seabreezes near the Coorong coast through the 19th-27th. Westward moving trough combining with upper low from about 24th to generate isolated to scattered afternoon and evening showers and thunderstorms, more likely in the north and eastern half. Locally heavy falls in thunderstorms, as well as hail in stronger cores. Another trough may extend from west later in period with heat developing ahead before cooler air and a new ridge moves in contracting shower and thunderstorm activity eastwards. Rainfall for period widely ranging from 5-30mm. Isolated falls in thunderstorms to 40mm. If trough shifts west, then bottom end rainfall totals likely increase to 15-25mm.
Lower SE
Weak upper low to west generating some high cloud in the north on 18th otherwise remaining mostly fine. Firm ridge to south with moderate to fresh S to SE winds with fresh seabreezes near the coast through the 19th-27th. Westward moving trough combining with upper low from about 24th to generate isolated to scattered afternoon and evening showers and thunderstorms, more likely in the north and eastern half. Locally heavy falls in thunderstorms, as well as hail in stronger cores. Another trough may extend from west later in period with heat developing ahead before cooler air and a new ridge moves in contracting shower and thunderstorm activity eastwards. Rainfall for period widely ranging from 5-30mm. Isolated falls in thunderstorms to 40mm. If trough shifts west, then bottom end rainfall totals likely increase to 15-25mm.
Western VIC
Weak upper low to west generating some high cloud in the north on 18th otherwise remaining mostly fine. Firm ridge to south with moderate to fresh S to SE winds with fresh seabreezes near the coast through the 19th-27th. Westward moving and deepening surface trough combining with upper low from about 24th to generate multiple days of humid weather with scattered afternoon and evening showers and thunderstorms, tending to rain at times with moderate to heavy falls developing in the north and east. Locally heavy falls in thunderstorms, as well as hail in stronger cores. Thunderstorm activity more isolated with southern and western extent as ridge influence increases. Another trough may extend from west later in period with heat developing ahead before cooler air and a new ridge moves in contracting shower and thunderstorm activity eastwards. Rainfall for period widely ranging from 15-35mm. Isolated falls in thunderstorms to 60mm. If trough shifts west, then bottom end rainfall totals likely increase to 20-30mm.
Final Notes
- Positive IOD rapidly weakening allowing waters to warm and moisture to build to the north and NW of the continent
- El Nino about to peak however influence already waning with increase in moisture from the Pacific into Eastern Australia
- Expected rapid uptick in shower and thunderstorm activity across the nation for the second half of month is upon us however upper lows combining with a deep and quasi stationary surface trough (Easterly Dip) will focus heavier falls across SE QLD & N NSW especially but also extending south into VIC and much later into SA to a lesser degree.
- Multiple days of high-end severe thunderstorms across the interior of SA and southern NT with destructive winds, giant hail, and intense rainfall together with prolific lightning
- Nature signs including heavy flowering on Silky Oak trees and ants in unusual places and in large numbers at that
- December likely a thundery month nationwide as moisture increases however expect some pushback from the SW as the current blocked pattern breaks down
- 2024 is looking like a wet year with many opportunities for significant rainfall, especially inland and across Eastern Australia with a good shot at a La Nina once more
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.
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