Showing posts with label weather. Show all posts
Showing posts with label weather. Show all posts

Wednesday 20 September 2023

The other shoe has finally dropped - El Niño has been declared by Australian Bureau of Meteorology


Click on image to enlarge



Central and eastern Pacific sea surface temperatures (SSTs) currently exceed El Niño thresholds. International climate models suggest some further warming of the central and eastern tropical Pacific Ocean is likely. All surveyed models indicate SSTs will remain above El Niño thresholds until at least the end of the 2023–24 southern hemisphere summer.

Bureau long-range forecasts are for SSTs up to 2.5 °C warmer than average off eastern Tasmania and in the eastern Tasman Sea from October to the end of 2023.


Click on image to enlarge


Australian Bureau of Meteorology, 19 September 2023:


ElNiño and positive Indian Ocean Dipole underway


An El Niño and a positive IOD are underway.


The declaration of these events, and their concurrence over spring, reinforces the Bureau's long-range rainfall and temperature forecasts, which continue to predict warmer and drier conditions for much of Australia over the next three months. The confirmation of an established El Niño increases the likelihood that the event will be sustained through the summer period.


Oceanic indicators firmly exhibit an El Niño state. Central and eastern Pacific sea surface temperatures (SSTs) continue to exceed El Niño thresholds. Models indicate further warming of the central to eastern Pacific is likely.


Broadscale pressure patterns over the tropical Pacific reflect El Niño, with the 90-day Southern Oscillation Index (SOI) at −7.7. Recent trade wind strength has been generally close to average, but was slightly weaker than average across the tropical Pacific in August 2023 for the first time since January 2020.


Overall, there are signs that the atmosphere is responding to the pattern of SSTs in the tropical Pacific and coupling of the ocean and atmosphere has started to occur. This coupling is a characteristic of an El Niño event and is what strengthens and sustains an event for an extended period. Climate models indicate this El Niño is likely to persist until at least the end of February. El Niño typically leads to reduced spring and early summer rainfall for eastern Australia, and warmer days for the southern two-thirds of the country.


A positive Indian Ocean Dipole is underway. The Indian Ocean Dipole (IOD) index is +1.25 °C for week ending 17 September. This is its fifth week above the positive IOD threshold (+0.40 °C). The longevity of this trend, combined with the strength of the dipole being observed and forecast, indicate a positive IOD event is underway. All models predict this positive IOD will persist to at least the end of spring. A positive IOD typically leads to reduced spring rainfall for central and south-east Australia.


When a positive IOD and El Niño occur together, their drying effect is typically stronger and more widespread across Australia.


The Madden–Julian Oscillation (MJO) is currently weak and is forecast to remain weak over the coming week.


The Southern Annular Mode (SAM) index is currently negative and is expected to remain negative for at least the coming week, before a possible return to neutral late in September. During spring, a negative SAM is associated with decreased rainfall across parts of the east in both NSW and Victoria, and increased rainfall over western Tasmania.


The long-rangeforecast for Australia indicates warmer and drier than average conditions are likely across most of southern and eastern Australia from October to December. The Bureau's climate model takes into account all influences from the oceans and atmosphere when generating its long-range forecasts.


Global warming


Global warming continues to influence Australian and global climate. Global sea surface temperatures (SSTs) were warmest on record for their respective months during April to August 2023. August 2023 SSTs were also the warmest globally for any month since observational records began in 1850. July and August 2023 were also respectively the hottest and second-hottest months globally in terms of 2-metre air temperature.


Australia’s climate has warmed by an average of 1.48 ± 0.23 °C since national records began in 1910. There has also been a trend towards a greater proportion of rainfall from high intensity, short duration rainfall events, especially across northern Australia. Southern Australia has seen a reduction, by 10 to 20%, in cool season (April to October) rainfall in recent decades. This is due to a combination of natural variability on decadal timescales and changes in large-scale circulation caused by an increase in greenhouse gas emissions.


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Thursday 18 August 2022

Still no assurances that increased heavy rainfall episodes in south east Australia have gone and 'normal' seasonal weather returned

 

Unfortunately it appears that north-east NSW can not yet rest easy.....


ABC News, 16 August 2022:


The odds of there being a third sodden summer in a row have shortened now the Bureau of Meteorology has declared a La Niña alert.


Renewed cooling in the tropical Pacific Ocean and models indicating La Niña is likely during spring and early summer have prompted the BOM to raise the El Niño Southern Oscillation Index scale to "alert", the last step before an official La Niña.


Four of seven climate models it surveys suggest La Niña could return by early to mid spring. The remaining three suggest levels will remain neutral but close to the La Niña threshold through to the end of 2022.


If the climate driver is declared, it would be the third consecutive La Niña summer.


Triple-dip La Niñas are relatively rare, having only occurred twice since 1950, in 1973-76 and 1998-2001.


But with catchments already primed and water storages full, the third wet year could signal disaster.


National water storage levels are currently sitting at 71.3 per cent, up 5 per cent on last year, while the Murray-Darling Basin is sitting at 92.2 per cent, up 12.4 per cent on this time last year.


Many dams up and down the east coast are now sitting at or over capacity….


With catchments sodden, it won't take much before the water has nowhere to go…..


This year the rainfall is being further charged by a negative Indian Ocean Dipole (IOD), which has already been declared.


Much like a La Niña, a negative IOD means there is extra moisture available, this time in the north-west.


Frontal systems can then tap into that moisture and drag it across the country, typically bringing wetter than average conditions for south-eastern Australia in winter and spring until the monsoon moves down and breaks up the cycle in early summer.


All La Niñas and IODs are different and there are no guarantees when it comes to forecasting.


But even if the Bureau's official La Niña thresholds are not met this summer, above average sea surface temperatures will likely aid rainfall.


At this point, there is a strong chance of a third La Niña, acting on already primed catchments, with a complementary IOD, which is likely to bring more rounds of flooding rains this spring and summer....


Insurance News, 16 August 2022:


Flood fears increase as likelihood of rare triple-dip La Nina rises


The Bureau of Meteorology has today issued a La Nina alert, meaning there’s now a 70% chance that the flood-inducing climate driver will develop this year.


It would be the third La Nina in a row – something that has only happened twice since 1950 – leading to fears of more heavy rain along the already flood-hit east coast of Australia.....


Australian Bureau of Meteorology, ENSO Outlook An alert system for the El Niño–Southern Oscillation, 16 August 2022:


ENSO Outlook moves to La Niña ALERT


The ENSO Outlook has [moved] to La Niña ALERT. This means that even though the El Niño–Southern Oscillation is currently neutral, the chance of La Niña forming in the coming months has increased to around 70%. This is roughly three times the normal likelihood of an event forming in any year.


This status change follows a renewal of cooling in the tropical Pacific Ocean towards La Niña thresholds over recent weeks, as well as the persistence of the Southern Oscillation Index (SOI) at La Niña levels and strengthened trade winds at La Niña levels. Climate models indicate further cooling is likely, with four of seven models suggesting La Niña could return by early-to-mid southern hemisphere spring.


A La Niña ALERT is not a guarantee that La Niña will occur, rather it is an indication that most of the typical precursors of an event are in place. La Niña conditions increase the chance of above average spring and summer rainfall in northern and eastern Australia.


Bureau climatologists will continue to closely monitor conditions in the tropical Pacific as well as model outlooks for further signs of La Niña re-emergence.


"The chance of a La Niña developing in the coming season has increased. When these criteria have been met in the past, a La Niña event has developed around 70% of the time.".....













La Niña Alert


Any three of the following criteria need to be satisfied:


  • Sea surface temperature: A clear cooling trend has been observed in the NINO3 or NINO3.4 regions of the Pacific Ocean during the past three to six months.

  • Winds: Trade winds have been stronger than average in the western or central equatorial Pacific Ocean during any two of the last three months.

  • SOI: The two-month average SOI is +7 or higher.

  • Models: A majority of surveyed climate models show sustained cooling to at least 0.8 °C below average in the NINO3 or NINO3.4 regions of the Pacific Ocean by the late winter or spring.


Thursday 12 May 2022

Eight days out from the 21 May 2022 federal general election and much of the NSW Northern Rivers region is on flood watch again


Australian Bureau of Meteorology (BOM):

Flood Watch for the Northern Rivers and Central West

Issued at 12:21 pm EST on Thursday 12 May 2022


Flood Watch Number: 3


MINOR FLOODING POSSIBLE IN THE NORTHERN RIVERS AND CENTRAL WEST FROM THURSDAY


A trough over western inland New South Wales will generate further moderate to heavy rain in many areas of the Central West on Thursday. This may cause minor flooding along the Castlereagh, Macquarie and Bell Rivers from Thursday night.


* Reissue to include Castlereagh *


River level rises have been observed from recent moderate rainfall in the Northern Rivers. Further moderate showers expected on Thursday may see river levels rise to minor flood levels.


Renewed minor flooding is also possible along the Bogan River where a flood warning is current.


The Bureau is continuing to monitor the situation and will issue further catchment specific warnings if and when required.


Catchment soil moisture is average.


The weather system is expected to cause flooding for the catchments listed. Flood Classes (minor, moderate, major) are only defined for catchments where the Bureau provides a flood warning service.


Catchments likely to be affected include:


Tweed and Rouse Rivers - minor flooding 

Brunswick River and Marshalls Creek - minor flooding

Wilsons River - minor flooding

Richmond River - minor flooding

Castlereagh River - minor flooding

Orange, Molong and Bell River - minor flooding

Turon and Macquarie Rivers to Burrendong Dam - minor flooding

Macquarie River d/s Burrendong Dam - minor flooding


Flood warnings are current for the Culgoa, Bokhara, Bogan, Paroo and Warrego Rivers.


For the latest flood and weather warnings see www.bom.gov.au/nsw/warnings/


For the latest rainfall and weather forecasts see www.bom.gov.au/australia/meteye/


For the latest rainfall and river level information see www.bom.gov.au/nsw/flood

 [my yellow highlighting]

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There is a chance of above median rainfall across much of the continent from 14 May 2022 to September 2022.


According to BOM long range forecasting there is also a 50-60% chance of the Page and Richmond electorates in the Northern Rivers region being “unusually wet” between 14 to 27 May 2022.


Stream Flow Forecast


Click on image to enlarge
















Climate outlook overview

Issued: 5 May 2022


Winter (June to August) rainfall is likely to be above median for most of Australia, except south-western Australia, the south-east coast, and southern Tasmania which have roughly equal chances of being above or below median.

June to August maximum temperatures are likely to be above median for northern, south-western, and south-eastern parts of Australia, but below median for broad areas of inland southern and central Australia.

Minimum temperatures for June to August are very likely to be warmer than median across almost all of Australia.

The weakening La Niña, the chance of a negative Indian Ocean Dipole, and other localised drivers are likely to be influencing this outlook.


Latest Climate Driver Update, 10 May 2022:


La Niña maintains strength


The 2021–22 La Niña event continues in the tropical Pacific, with little change in strength in the past few weeks.


Several indicators of La Niña, including tropical Pacific sea surface temperatures, cloudiness near the Date Line, and the Southern Oscillation Index (SOI), have maintained or slightly increased their strength over the past fortnight. However, beneath the surface of the tropical Pacific, waters have warmed closer to neutral El Niño–Southern Oscillation (ENSO) levels.


Most climate models surveyed by the Bureau indicate a return to neutral ENSO by the early southern hemisphere winter. Only one of seven models continues La Niña conditions through the southern winter. La Niña conditions increase the chances of above average rainfall for much of eastern Australia, while neutral ENSO has little influence on rainfall patterns.


The Indian Ocean Dipole (IOD) is neutral. All climate model outlooks surveyed suggest a negative IOD may develop in the coming months. While model outlooks have low accuracy at this time of year and hence some caution should be taken with IOD outlooks beyond May, there is strong forecast consistency across international models. A negative IOD increases the chances of above average winter–spring rainfall for much of Australia. It also increases the chances of warmer days and nights for northern Australia.


The Southern Annular Mode (SAM) index is currently positive and is forecast to remain positive for the coming four weeks. During autumn SAM typically has a weaker influence on Australian rainfall, but as we approach winter, positive SAM often has a drying influence for parts of south-west and south-east Australia.


The Madden–Julian Oscillation (MJO) has recently strengthened in the western Indian Ocean. Most climate models indicate the MJO will briefly weaken, and then re-strengthen again later this week in the Maritime Continent or western Pacific region. Should the MJO re-strength in the Maritime Continent region, it can enhance rainfall in north-eastern Australia. It also typically increases cloudiness to Australia's north.


Climate change continues to influence Australian and global climate. Australia's climate has warmed by around 1.47 °C for the 1910–2020 period. Southern Australia has seen a reduction of 10–20% in cool season (April–October) rainfall in recent decades. There has also been a trend towards a greater proportion of rainfall from high intensity short duration rainfall events, especially across northern Australia. [my yellow highlighting]



Tuesday 15 March 2022

NSW predicted rainfall over April, May and June 2022


It would appear there is some likelihood that the next three calendar months will see temperatures rise above median and a 60 per cent chance of an increase in median rainfall across New South Wales generally.


With the predicted above median rainfall occurring inland as far as Tibooburra & Broken Hill and along the length of the coastal zone. 


The Northern NSW section of this coast zone - from Clarence Valley  to Tweed Shire and inland as far as Lismore City - having a 60 to 74 per cent chance of exceeding median rainfall.


Brief Outline


Australian Bureau of Meteorology (BOM), retrieved 14 March 2022:


Climate outlook overview

Issued: 10 March 2022


April to June rainfall is likely to be above median for most of northern and eastern Australia, with small areas of south-west WA and western Tasmania likely to be below median. Elsewhere, there are roughly equal chances of above or below median rainfall.

April to June maximum temperatures are likely to be above median for western, northern and south-eastern parts of Australia. Elsewhere, there are roughly equal chances of warmer or cooler days.

Minimum temperatures for April to June are likely to be warmer than median across virtually all of Australia.

Climate influences include the weakening La Niña in the Pacific Ocean.


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La Niña remains active in the tropical Pacific. Outlooks indicate the La Niña is likely to end around mid-autumn 2022, with a return to neutral El Niño–Southern Oscillation conditions. While this La Niña event is weakening, it is expected to continue to contribute to the wetter than median outlooks for parts of eastern Australia.


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BOM: Median rainfall April-June (1981-2018) 











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Wetter April to June likely for northern and eastern Australia

Issued: 10 March 2022


April to June rainfall is likely to be above median for most of the NT, Queensland, south-east SA, and most of NSW (chance of exceeding median is greater than 60%). Some small areas of south-west WA and western Tasmania are likely to be below median (chance of exceeding median is less than 40%). Elsewhere, there are roughly equal chances of above or below median rainfall (chance of exceeding the median is close to 50%).

There is an increased chance of unusually high rainfall (in the top 20% of historical records) for April to June across the northern half of the NT, northern and western Queensland and small areas of western and coastal NSW (1.5 to 2.5 times the usual chance). However, it should be noted that seasonal rainfall at this time of the year is starting to decrease, so unusually high rainfall for these areas isn't as high as recent months.

While the April outlook reflects the three-month outlook, the May outlook suggests below median rainfall is likely for south-western Australia, and western Tasmania, and only a small part of central Queensland is likely to be above median.

Past accuracy for April to June rainfall is moderate to high for most areas of Australia, with low to very low accuracy across much of eastern WA, northern and western SA, the central NT, western Victoria and southern Tasmania.


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Warmer April to June days and nights for most areas

Issued: 10 March 2022


April to June maximum temperatures are likely to be above median for most of WA, the northern and central NT, Queensland, northern and southern NSW, south-east SA, Victoria, and Tasmania (greater than 60% chance). Elsewhere, there are roughly equal chances of warmer or cooler days (chance of exceeding the median is close to 50%).

There is an increased chance of unusually high maximum temperatures (in the top 20% of historical records) for April to June over most of WA, the northern and central NT, most of Queensland except the far south, most of Victoria, and Tasmania (1.5 to 4.0 times the usual chance), with the highest chances in the tropical north, and Tasmania.

Minimum temperatures for April to June are likely to be warmer than median almost Australia wide (chances are greater than 60%), with much of northern and eastern Australia very likely (chances are greater than 80%).

There is an increased chance of unusually high minimum temperatures (in the top 20% of historical records) for April to June over most of Australia except much of southern WA and western SA (1.5 to 4.0 times the usual chance). The highest likelihoods are across far northern Australia and Tasmania.

Past accuracy for April to June maximum temperatures is high to very high for almost all of Australia, with moderate accuracy in a band stretching through central WA and across most of SA. For minimum temperatures, accuracy is high to very high across northern Australia, grading to low to very low accuracy across southern parts of the mainland. Tasmania has moderate accuracy in the south, with low accuracy in the north.


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Historical median and mean rainfall Lismore, Ballina, and Grafton NSW for April, May and June.


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Friday 26 November 2021

La Niña's arrival in the tropical Pacific may herald high flow river levels on the NSW coast during December 2021



Australian Bureau of Meteorology (BOM):


Climate outlook overview, 18 November 2021:


  • December to February rainfall is likely to be above median for the eastern half of the eastern States, with highest chances along eastern Queensland.

  • There is an increased chance of unusually high rainfall (in the top 20% of historical records) for December to February for parts of the eastern States (1.5 to 2.5 times the usual chance).

  • December to February maximum temperatures are likely to be above median for much of northern and western Australia, as well as parts of the south-east. Below median daytime temperatures are likely for eastern NSW.

  • Minimum temperatures for December to February are likely to be warmer than median for most of Australia, with southern WA and western SA having roughly equal chances of warmer or cooler than median nights.

  • The developing La Niña conditions in the Pacific Ocean, and the La Niña (SAM) phase are likely influencing the above median rainfall outlooks.


 Climate Driver Update, 23 November 2021:


La Niña established in the tropical Pacific


La Niña has become established in the tropical Pacific. The Bureau's ENSO Outlook has been raised to LA NIÑA. Climate models suggest this La Niña will be short-lived, persisting until the late southern hemisphere summer or early autumn 2022. La Niña events increase the chance of above average rainfall across much of northern and eastern Australia during summer.


Several indicators of the El Niño–Southern Oscillation (ENSO) now show clear La Niña patterns. Sea surface temperatures in the tropical Pacific are close to La Niña thresholds, with climate model outlooks expecting them to cool further. In the atmosphere, cloud and wind patterns are typical of La Niña, indicating the atmosphere is now responding to, and reinforcing, the changes observed in the ocean.


The negative Indian Ocean Dipole (IOD) is approaching its end, with oceanic index values in the neutral range. However, cloud and wind patterns across the eastern Indian Ocean suggest some IOD influence remains. All models indicate the IOD will remain neutral for the coming months, consistent with its typical seasonal cycle. A negative IOD increases the chances of above-average spring rainfall for much of southern and eastern Australia.


The Madden–Julian Oscillation (MJO) is currently over the Maritime Continent region at weak to moderate strength. The MJO is forecast to progress eastwards across the Maritime Continent and into the western Pacific over the coming fortnight, increasing the chances of above average rainfall across northern Australia and the Maritime Continent, to Australia's north.


The Southern Annular Mode (SAM) has generally been positive for several weeks. It is forecast to remain at positive levels to the end of the year. A positive SAM during summer typically brings wetter weather to eastern parts of Australia, but drier than average conditions for western Tasmania.


Climate change continues to influence Australian and global climate. Australia's climate has warmed by around 1.44 °C for the 1910–2019 period. Rainfall across northern Australia during its wet season (October–April) has increased since the late 1990s. In recent decades there has been a trend towards a greater proportion of rainfall from high intensity short duration rainfall events, especially across northern Australia.




Wednesday 12 May 2021

The El Niño–Southern Oscillation (ENSO) is expected to remain in neutral phase at least until October 2021


Australian Bureau of Meteorology, Climate Driver Update, 11 May 2021:


Southern Annular Mode positive; El Niño–Southern Oscillation neutral


The El Niño–Southern Oscillation (ENSO) continues at neutral levels. Climate model outlooks currently indicate this neutral phase will last at least until October.


Oceanic indicators of ENSO persist at neutral levels, with Pacific sea surface temperatures close to the long-term average across most of the equatorial region. Beneath the surface, temperatures are near-average, with slightly warmer than average waters across much of the sub-surface. Atmospheric indicators such as the Southern Oscillation Index (SOI) and cloud patterns are also close to average. Trade winds have been stronger than average in the far west, but near average elsewhere.


The Madden–Julian Oscillation (MJO) is over the Indian Ocean region. It is forecast to move eastwards across Australian longitudes over the coming fortnight. When the MJO is active over the eastern Indian Ocean and Australian longitudes at this time of year, above average rainfall is more likely over the Maritime Continent to Australia's north. Additionally, it typically acts to strengthen easterly winds on Queensland’s tropical east coast and increase temperatures across tropical Australia.


The Southern Annular Mode (SAM) has been positive for the past week. It is expected to remain positive for the coming fortnight. SAM typically has little influence on Australian rainfall during autumn, but may have a drying influence for parts of south-west and south-east Australia over the coming fortnight.


The Indian Ocean Dipole (IOD) is currently neutral. Climate model outlooks suggest the IOD is most likely to remain neutral during the first half of winter. Three of the five models indicate negative IOD thresholds may be reached during winter or spring. The accuracy of IOD forecasts made during autumn is generally lower than at other times of the year, but improves in winter. A negative IOD increases the chances of above average winter-spring rainfall for much of southern Australia.


Climate change continues to influence Australian and global climate. Australia's climate has warmed by 1.44 ± 0.24 °C over 1910–2019, while southern Australia has seen a reduction of 10–20% in cool season (April–October) rainfall in recent decades. [my yellow highlighting]


Climate Model Summary for June to October 2021 at:


Next update expected on 25 May 2021


It appears that temperatures, winds, convection (rising air), and rainfall across the tropical Pacific may remain near their long-term averages, but temperatures in Australia's north may be warmer than usual and rainfall across much of southern Australia may increase from June to October.