September update 2023 SA
September update 2023 SA
*Forecast prepared between September 17th-19th 2023
Review:
G’Day everyone, hope you are keeping well. Mid-September is here and getting well overdue for an update on proceedings for the month, a month that has really thrown the mercury around in a short space of time with very large diurnal ranges. A quick recap on the progress so far first.
A fairly solid cold front very late on the 6th and during the 7th delivered a band of rain across agricultural areas with some useful falls generally in the 10-20mm range although totals did drop off east of the ranges and much further north. Behind this, much colder air moved through with numerous ‘coldies’ with small hail and the odd isolated cold air rumble. The wind also was significant with this system with a small but tight low slinging up during the evening of the 7th bringing 70-80km/hr gusts, with Neptune Island (not unusual) recording the highest gust at 107km/hr. The high-end potential across eastern districts overnight 7th and into the early hours of the 8th perhaps did not quite reach expected levels as per the quick update with maximum gusts around 70-75km/hr. That being said, the coldness of the system combined with the wind and showers was significant to warrant a Sheep Graziers Advice. To top it off, some snow was reported near Hallett and up on Mount Bryan.
After this cold air, we expected a strong high to move in quickly to create a snap frost and whilst this did occur, a weak front sliding below the mainland, threw up enough moisture, westerly wind and low cloud to mitigate minimums across the SE Districts. Numerous frosts of the slight to moderate grade still occurred further north with isolated heavier pockets in the Upper North.
However, after this we saw the main turn in the month, a turn that has been building silently over the WA interior. Heat has now begun to advect SE ahead of every frontal system. A particularly strong system slammed into SW WA last week with significant rainfall, destructive winds with some tornadic activity. However, this system lost 99% of its moisture by the time it reached SA with only mere dregs drifting across. The blocking Tasman High just deflected the system SE with only the pressure gradient ahead causing warm to hot N winds to freshen, quite strong and gusty at times on the 14th. Then a second round of heat with more intensity moved SE as an upper ridge intensified inland increasing atmospheric thickness to levels normally seen in December. Ceduna reached a top of 39.8C which was a September record with numerous other centres across Eyre Peninsula and the Upper North passing 35C. These hot and dry days with curing N winds have no doubt taken a drastic toll on crops which only one week prior were hit with frost.
Meteorological Discussion:
Now for the remainder of this month, there hasn’t been a great change in expectations from the original outlook with a general drying and warming trend showing its hand. However there still will at least be some systems worth talking about and the associated weather.
Currently we have a fairly large and broad area of low pressure located well to the south of the mainland which is directing a westerly flow across the agricultural areas. This is also contributing to the negative SAM at this current point in time. Inland however the warmth is still remaining with mid to high 30’s temperatures becoming a regular occurrence across the interior. A weak front attached to an enormous, large low centred well south of Tasmania which is making up a bulk of one node of the Longwave Trough will traverse the south of the state early on the 20th with a broken band of showers, more isolated north of about Adelaide in latitude with most precipitation confined to the Lower SE and Southern Coasts and ranges. There won't be much inland penetration with this one, especially not across Eyre Peninsula or the Upper North and Riverland, where many centres will be lucky to see more than a wind change and some cloud.
A large high will then build behind this front on the and move eastwards steadily, however as it does so a final weak front will flip up from the SW in the onshore flow late evening on the 20th and into the early hours of the 21st and deliver and short burst of shower activity to similar areas of the first front. This will rapidly clear during the 21st as the new high moves east and for the most part the day should clear out to be relatively fine.
This high will strengthen as it moves east to reach approximately 1033-1034hpa in strength in the same area that all the dominant highs have been planting – the good ol Tasman and this will bring back warmer air from the interior and direct it back south. Temperatures will then begin to rise into the high 20’s and low to mid 30’s across the agricultural areas ahead of a weak trough extending from the west by about the late 24th or 25th. The trough of low pressure should then extend eastwards with isolated showers and thunderstorms, with a gusty westerly change like. These sorts of changes will be commonplace in spring this year.
Beyond this another large high will move eastwards keeping the pattern fairly mobile with the highs then slowing down in the Tasman as they set up the block. All this will keep doing is force the heat to bake over the interior of WA and then get advected SE ahead of every change gradually increasing in potential heat wise as we advance through October and November. I expect 40C temperatures across agricultural areas during October with 42-45C temperatures during November. Numerous temperature records will likely fall, although knocking some off from 2009 may be a challenge. Whilst we may see temperatures as high as that or even higher in isolated scenarios, the longevity of that heatwave is unlikely to be repeated this year as the pattern is likely to be a little bit too mobile.
The early outlook for October broadly is an extension of September but with deeper upper ridges being met with vigorous spring troughs and fronts however rainfall will be patchy. Cold air will still push in behind the systems, so wild temperature fluctuations are likely.
November sees the moisture begin to creep in and with that instability also. Given it will be early in the piece, the nature of the thunderstorm activity will be primarily high based with plenty of lightning and fire threats as well as damaging wind. Large hail in the stronger thunderstorms will also be a feature with numerous dynamic trough systems likely after heat.
December will still be quite hot with plenty of heat but perhaps some better troughs with a bit more moisture at times than November. But nothing at this stage points to any of the remaining months of the year being above average rainfall wise, only temperature wise.
Climate Drivers:
The El Nino in the Pacific has officially been declared by the Bureau but has not made much headway in the last 2 weeks apart from a slight shift in the location of the warmest anomalies which has now begun to inch westwards from the far Eastern Pacific as there has been some slight cooling in that area. The final magnitude is in the weak to moderate category as most other factors are all pointing in the El Nino direction but not at significant levels. We just have the remember that the entire Pacific Basin is quite warm which will hold some weight in heat and moisture release into the atmosphere for 2024.
The Indian Ocean has really come to the forefront in the past 2 weeks with a significant strengthening of the Positive Indian Ocean dipole (edit which has also been declared at the same time as El Nino by the Bureau). At the last update on September 12th, it was +1.10C with the Positive threshold being +0.40C. On current view with the significant cold-water upwelling in the last 4-5 days, I suspect that is now closer to +1.3 to 1.4CC which is a moderate event and not far off strong which is around +1.8C to +2C. That may be a bridge too far, but it will come close I think with October typically being a peak in the event. The effects from this however are clearly already being felt with rapid injections of heat bringing hot and dry conditions to agricultural areas in the blink of an eye. This will only increase through October and November, and I certainly expect some very hot conditions through November but with an increasing thundery signature as moisture piles into the very large and dominant heat low and associated troughs, albeit chiefly mid-level moisture favouring high based thunderstorms.
The SAM has been slightly negative of late which is a classic sign of El Nino. Strong El Nino’s tend to keep the SAM more negative than positive through spring and summer so to see this is a sign that despite the El Nino not being strong, there is some influence starting to occur. Typically with a negative SAM we will see a barrage of wet weather but with such fast moving systems and a lack of moisture being available to them (thanks to the now raging Positive IOD) we end up with hot dry winds ahead as the pressure and temperature gradients remain large but a distinct lack of rainfall on the change itself with mostly higher based rainfall which leads to lower totals a majority of the time. Don’t be surprised if we still have a couple more colder blasts through spring despite the heat building over inland WA. These systems typically have very strong and damaging westerly changes and can raise dust.
The MJO is currently weak over the Indian Ocean but is expected to gain some momentum in early October as it pushes across the Pacific and into phases 7 and 8 which will give further fuel to intensify the El Nino and likely push it towards maturity which at this stage is expected around November to December.
Districts:
Eyre Peninsula
Weak front clipping coast early 20th with isolated showers about Lower Eyre Peninsula. Remaining mostly dry inland. Second weak front late 20th or early 21st with light showers before new strong high clears activity. Temperatures rising as winds turn overland from the NE to N through till about the 25th with hot conditions developing in the west and north. Trough and cold front due around 25th to 26th with isolated showers and thunderstorms together with a strong and gusty westerly change with cooler conditions to follow. New high once again to move in with a return to warmer conditions to round out the month with likely hot weather by early October. Rainfall for period 3-6mm about Lower Eyre Peninsula decreasing to less than 1-2mm inland.
Upper North
Weak front clipping coast early 20th with isolated showers in the south. Remaining mostly dry further north. Second weak front early 21st with light showers in the far south and near the Spencer Gulf coast and ranges before new strong high clears activity. Temperatures rising as winds turn overland from the NE to N through till about the 25th with hot conditions developing in the north. Trough and cold front due around 26th with isolated showers and thunderstorms together with a strong and gusty westerly change with cooler conditions to follow. New high once again to move in with a return to warmer conditions to round out the month with likely hot weather by early October. Slight frost risk early 22nd. Rainfall for period generally less than 3mm, and down to less than 1mm in the north and east off the back of the ranges.
Lower North
Weak front clipping coast early 20th with isolated showers, tending scattered in the south briefly. Second weak front early 21st with light showers before new strong high clears activity. Temperatures rising as winds turn overland from the NE to N through till about the 25th with warm to hot
conditions developing in the north and west. Trough and cold front due around 26th with isolated showers and thunderstorms together with a strong and gusty westerly change with cooler conditions to follow. New high once again to move in with a return to warmer conditions to round out the month with likely hot weather by early October. Slight frost risk early 22nd. Rainfall for period generally 3-5mm, and down to less than 1-2mm in the north and east off the backs of the ranges.
Yorke Peninsula
Weak front clipping coast early 20th with isolated showers, scattered about the southern half of the Peninsula. Second weak front late 20th or early 21st with light showers before new strong high clears activity. Temperatures rising as winds turn overland from the NE to N through till about the 25th with warm to hot conditions developing in the north. Trough and cold front due around 25th to 26th with isolated showers and thunderstorms together with a strong and gusty westerly change with cooler conditions to follow. New high once again to move in with a return to warmer conditions to round out the month with likely hot weather by early October. Slight frost risk in the north early 22nd. Rainfall for period 4-8mm about the foot and lower portions of the Peninsula but decreasing to less than 1-2mm in the north.
Kangaroo Island
Weak front clipping coast early 20th with a broken band of showers. Second weak front late 20th with light showers before new strong high clears this activity. Temperatures rising as winds turn overland from the NE to N through till about the 25th with warmer conditions developing. Trough and cold front due around 25th to 26th with isolated showers and thunderstorms together with a strong and gusty westerly change with cooler conditions to follow. Potentially damaging winds near a low centre behind the change if it forms close to the island. New high once again to move in with a return to warmer conditions to round out the month with likely warm to even hot weather by early October. Rainfall for period generally about 4-8mm, but lower totals towards the eastern end down to 2-3mm or so.
Adelaide Plains
Weak front clipping coast early 20th with isolated showers, scattered about the southern suburbs and most foothills. Second weak front late 20th or early 21st with light showers before new strong high clears activity. Temperatures rising as winds turn overland from the NE to N through till about the 25th with warm to hot conditions developing in the north. Trough and cold front due around 25th to 26th with isolated showers and thunderstorms together with a strong and gusty westerly change with cooler conditions to follow. New high once again to move in with a return to warmer conditions to round out the month with likely hot weather by early October. Slight frost risk about the outer northern plains early 22nd. Rainfall for period 3-6mm generally and possibly to 8mm about the foothills but decreasing to less than 3-4mm in the north.
Mt.Lofty Ranges
Weak front clipping coast early 20th with a broken band of showers, more isolated towards the northern ranges and Barossa region. Second weak front late 20th or early 21st with light showers before new strong high clears activity. Temperatures rising as winds turn overland from the NE to N through till about the 25th with warm to hot conditions developing about the Barossa, chiefly. Trough and cold front due around 25th to 26th with isolated showers and thunderstorms together with a strong and gusty westerly change with cooler conditions to follow, possibly damaging about higher peaks subject to low position. New high once again to move in with a return to warmer conditions to round out the month with likely hot weather by early October. Slight frost risk about low lying valleys early 22nd. Rainfall for period 5-10mm generally and possibly to 12mm about the higher peaks and known wet spots but decreasing to less than 3-4mm in the north and also off the back side of the ranges.
Riverland/Mallee
Weak front clipping coast early 20th with isolated showers, scattered over the Southern Mallee. Second weak front early 21st with light showers in the southern half of the Mallee only before new strong high clears activity. Temperatures rising as winds turn overland from the NE to N through till about the 25th with hot conditions developing across the Riverland and warm to hot over much of the Mallee. Trough and cold front due around 26th with isolated showers and thunderstorms together with a strong and gusty westerly change with cooler conditions to follow. New high once again to move in with a return to warmer conditions to round out the month with likely hot weather by early October. Slight frost risk early 22nd. Rainfall for period generally 2-5mm across the Southern half of the Mallee and down to less than 1mm in the north and east of the Mallee and over the Riverland.
Upper SE
Weak front clipping coast early 20th with isolated showers, scattered towards the Coorong coast and the Lower SE border. Second weak front late 20th and early 21st with another band of showers, chiefly in the south before new strong high clears activity. Temperatures rising as winds turn overland from the NE to N through till about the 25th with warm to hot conditions throughout. Trough and cold front due around 26th with isolated showers and thunderstorms together with a strong and gusty westerly change with cooler conditions to follow. New high once again to move in with a return to warmer conditions to round out the month with likely hot weather by early October. Slight frost risk early 22nd. Rainfall for period generally 2-5mm across the district, grading to 5-8mm in the far south.
Lower SE
Weak front clipping coast early 20th with a broken band of showers. Second weak front late 20th and early 21st with another band of showers before new strong high clears activity. Temperatures rising as winds turn overland from the NE to N through till about the 25th with warm conditions throughout. Trough and cold front due around 26th with isolated showers and thunderstorms together with a strong and gusty westerly change with cooler conditions to follow. New high once again to move in with a return to warmer conditions to round out the month with likely hot weather by early October. Slight frost risk early 22nd. Rainfall for period generally 5-10mm across the district however isolated 15mm falls are possible in the far south.
Western VIC
Weak front clipping coast early 20th with a broken band of showers, chiefly about the SW District with activity much more isolated with northern extent, especially the Mallee. Second weak front early 21st with another band of showers over the Wimmera and south of before new strong high clears activity. Temperatures rising as winds turn overland from the NE to N through till about the 25th with warm conditions throughout. Trough and cold front due around 26 or 27thth with isolated showers and thunderstorms together with a strong and gusty westerly change with cooler conditions to follow. New high once again to move in with a return to warmer conditions to round out the month with likely hot weather by early October. Slight frost risk early 22nd. Rainfall for period generally 5-10mm across the SW district however isolated 15mm falls are possible in the far south near the coast. Totals down to 2-5mm about the Wimmera and less than 2mm for the Mallee.
Final Notes
- Positive IOD and El Nino declared with the former having the greatest influence on our weather despite the main noise for El Nino in media
- Fast moving, largely dry but windy systems throughout the remainder of September and much of October
- Increasing heat through October and especially November
- High based thunderstorms more likely from October and especially November to December with a risk of fire from plentiful Cloud to ground (CG) bolts
- Watch for numerous heat records to be set before the end of the year
- 2024 should see increased moisture through the autumn period as the breakdown of the El Nino and warm SST pattern
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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