Weekly climate hazards outlook - Recent conditions and outlooks Operational Climate Services 23 September 2021
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Weekly climate hazards outlook Recent conditions and outlooks Operational Climate Services 23 September 2021
National severe weather outlook: September 2021–April 2022 summary
Impact Likelihood compared to recent decades
Widespread flooding More likely
Coastal flooding / erosion More likely
Severe storms Similar
Bushfire risk Similar, increased for parts of Qld/NSW
Heatwave Similar spring, increased summer
Tropical cyclones More likely
Marine heatwave More likely
Drought Less likely
Dust Less likely
Severe weather summary
• Flood risk
• Bushfire risk
4
Flooding influences in coming weeks
Very much above
average
Above average
Average
Below average
Very much below
average
1 – 22 September 2021 Four weeks: 20 Sep – 17 Oct 2021
Top metre soil moisture Rainfall anomalies
Model run date 20/09/2021
• Soil moisture is above-average in eastern Victoria, parts of NSW and southern Qld, parts of southern WA,
western Tasmania and across northern Australia
• More rain on wet soils means increased risk of high runoff and flooding
Forest Fire Danger Index (FFDI) summary
Months 1 & 2 and Seasons 1 & 2
• September: Above-median FFDI likely for much of
WA, western Tasmania and parts of SA and Vic;
broadly near- to below-median FFDI elsewhere.
• October: Below-median FFDI likely for most regions
apart from western WA, western Tas and near the
SA/Vic border.
• September–November: Below-median FFDI likely for
most regions apart from western WA, western Tas and
near the SA/Vic border.
• October -December: Below-median FFDI likely for
most regions apart from much of WA, and parts of
western Tas and near the SA/Vic border.
Climate influences summary
• Indian Ocean Dipole (IOD)
- A negative IOD is underway
- A negative IOD typically increases the likelihood of above-average rainfall
across much of Australia during the winter-spring period
• El Niño-Southern Oscillation (ENSO)
- A La Niña WATCH has been issued, meaning around a 50% chance of La
Niña developing in 2021—twice the normal likelihood
• Madden-Julian Oscillation (MJO)
- Influence has shifted to the northern hemisphere, less impact over
Australia
• Southern Annular Mode (SAM)
- SAM is currently positive and expected to remain positive for the coming
week.
- During spring, positive SAM typically increases likelihood of above-average
rainfall for parts of south-eastern Australia
• Long-term trends
- Australia's climate has warmed by ~1.44°C over the 1910–2019 period,
while southern Australia has seen a reduction in cool season (April–
October) rainfall in recent decades
- These trends can become more apparent in the outlooks when other
climate drivers are neutral
Climate and severe weather
outlooks
• Rainfall and temperature: weekly, monthly &
seasonal outlooks
• Heavy rainfall risk
• Flood risk
• Severe frost risk
• Strong wind, MSLP and cloudiness outlooks
• Bushfire seasonal outlook
10
October 2021 outlook
Chance of above median
Maximum temperature Minimum temperature Rainfall
• Above-median daytime temperatures very likely in far northern Australia and Tasmania; near to below
median elsewhere
• Above-median minimum temperatures likely for most regions apart from WA and parts of SA
• Near to below median rainfall in WA and western Tas, mostly above-median rainfall elsewhere
October – December 2021 outlook
Chance of above median
Maximum temperature Minimum temperature Rainfall
• Above-median daytime temperatures very likely in parts of far northern Australia and Tasmania; near to
below median elsewhere
• Above-median minimum temperatures very likely for most regions apart from southern WA
• Near to below median rainfall for most of WA and western Tas, mostly above-median rainfall elsewhere
November 2021 – January 2022 outlook
Chance of above median
Maximum temperature Minimum temperature Rainfall
• Above-median daytime temperatures likely in parts of the far north and Tasmania; near to below median
elsewhere
• Above-median night-time temperatures likely for most regions
• Near- to below-median rainfall for most of WA and western Tasmania, mostly above-median elsewhereRainfall anomaly forecast
October 2021 November 2021 October – December 2021
Experimental product
Typical rainfall: Typical rainfall: Typical rainfall: Maps not issued publicly
October November October-December Not for wide distributionWeekly rainfall outlooks
Week 1 (weather model) Week 2 (climate model) Week 3 (climate model)
23 – 29 September 27 September – 3 October 4 – 10 October
Experimental product
Maps not issued publicly
Not for wide distribution
• Week 1: significant rainfall totals (25+ mm) in western Tasmania, Vic/NSW alpine, and far SW WA
• Weeks 2-3: significant totals for western Tasmania, Vic/NSW alpine and Tablelands
• Week 1: ADFD (GFE–forecaster input) forecast
• Weeks 2 & 3: 50% chance of exceeding rainfall amount (ACCESS-S)Probability of 30 mm rainfall in 3 days
Week 2: 27 Sept – 3 October Week 3: 4 – 10 October Weeks 3+4: 4 – 17 October
Experimental product
Maps not issued publicly
Not for wide distribution
• Weeks 2 & 3: Moderate (50-75%) chance of 3-day totals exceeding 30 mm across western Tasmania and
alpine areas of Vic/NSW
• Weeks 3 + 4: Moderate to High (>50%) chance of 3-day totals exceeding 30 mm across western Tasmania
and alpine areas of Vic/NSW, parts of SE Qld and NE NSWWeek 2: 27 September – 3 October 2021 outlook
Maximum temperature anomaly Minimum temperature anomaly Rainfall anomaly
Experimental product
Maps not issued publicly
Not for wide distribution
• Average to above-average daytime temperatures likely for much of eastern Australia; below average for
much of WA, southern SA and eastern Qld/NE NSW
• Average overnight temperatures likely for much of eastern Australia; below average for much of WA,
southern SA, western Vic and eastern Qld/NE NSW
• Near to above average rainfall likely much of eastern mainland; below-average parts WA, SA and W TasWeek 3: 4 – 10 October 2021 outlook
Maximum temperature anomaly Minimum temperature anomaly Rainfall anomaly
Experimental product
Maps not issued publicly
Not for wide distribution
• Average to above-average daytime temperatures likely for most regions; below average parts of central east
and WA
• Average to above-average night-time temperatures likely most regions
• Near to above average rainfall likely much of eastern mainland; below-average parts WA, S Vic and W TasFrost potential: chance of temperatures below 2 °C
Week 2: 27 Sept – 3 October Week 3: 4 – 10 October Weeks 3+4: 4 – 17 October
Experimental product
Maps not issued publicly
Not for wide distribution
• Week 2 & 3: High (>70%) chance of frost for Tasmania, inland and elevated parts of Vic and NSW, and
elevated parts of south-east SA
• Weeks 3+4: High (>70%) chance of frost for Tasmania, inland and elevated parts of Vic and NSW, and
elevated parts of south-east SAWind direction, cloud and MSLP anomaly outlook
Week 2: 27 Sept – 3 October Week 3: 4 – 10 October Weeks 3+4: 4 – 17 October
Experimental product
Maps not issued publicly
Not for wide distribution
• Week 2: Anomalously low MSLP over much of the mainland, with westerly anomalies in the north;
enhanced north-easterly flow for parts of eastern Australia
• Weeks 3+4: Anomalously low MSLP over northern parts; anomalously high MSLP far southAustralian Seasonal Bushfire Outlook: September–November 2021
• The above-normal fire potential over northern New South Wales and south-
eastern Queensland are driven by grass and crop growth in these areas.
• In Western Australia, the above-normal fire potential in the north is driven by
grass growth and dry soil in this area.
• Below-normal fire potential predicted across the ACT, NSW and Victoria is a
result of vegetation recovering from the 2019-20 bushfire season
• While the current negative Indian Ocean Dipole increases the likelihood of
above-average spring rainfall for the eastern two-thirds of the mainland, the
climate could rapidly transition back to a neutral state from December.
• Enhanced grass growth over spring may lead to above-normal fire risk during
summer if weather conditions are conducive for drying of abundant fuels.
• It is important to remember that fire is a regular occurrence across Australia,
and areas designated as normal fire potential may still experience fire. Normal
fire risk does not mean there is no risk.
• This map incorporates weather and fuel information, as well as the rainfall
outlook
• For more information: Bushfire Seasonal Outlook for Spring 2021Severe storms
Thunderstorm asthma
• In Victoria, forecast service resumes 1st October
2021 and runs until end of December (typical grass
pollen season)
• Distributed by Vic Emergency, partnered by the
Bureau of Meteorology
• The 2021 negative Indian Ocean Dipole (IOD) is the
first negative IOD since 2016, the year of the
Melbourne thunderstorm asthma event
• Severe thunderstorms bring heavy rainfall, flash flooding, damaging winds, and large hail
• The Melbourne Thunderstorm Asthma event occurred in 2016, the last year prior to 2021 that a negative
Indian Ocean Dipole was active
• Increased grass growth in spring could increase the thunderstorm asthma risk due to above-average pollen
levelsTropical cyclone formation outlook Probability of tropical cyclone intensity surface wind: • Week 2 (28 Sep-4 Oct): Low-Moderate (10-40%) chance of TC forming in western North Pacific Ocean; Low (
Recent conditions
• Current water storages
• Recent rainfall and maximum temperatures
• Drought conditions
• Recent soil moisture
25Water storages as at 19 September 2021
Water storages as at 22 September 2021
Rainfall and maximum temperatures (anomalies)
Recent conditions (2021-to-date)
Rainfall anomalies: Maximum temperature anomalies:
1 January – 23 September 2021 1 January – 22 September 2021
• Rainfall (Jan–Aug 21): Australia 1% above average | Australia wettest Jan-Aug since 2017
• Max. temperature (Jan–Aug 21): Australia 0.67 °C above average| Australia coolest Jan–Aug since 2012Rainfall and maximum temperatures
Recent conditions (2020)
Rainfall deciles: Maximum temperature deciles:
January–December 2020 January–December 2020
• Rainfall (2020): Australia 4% above average | No states/territories in top/bottom 10
• Max. temperature (2020): Australia 1.24 °C above average, 8th highest on record | WA 2nd highest (behind
2019), NT 5th highest, Qld 8th highest on recordRainfall and maximum temperatures (deciles)
Recent conditions (2021-to-date)
Rainfall deciles: Maximum temperature deciles:
January – August 2021 January – August 2021
• Rainfall (Jan–Aug 21): Australia 1% above average | Australia wettest Jan-Aug since 2017
• Max. temperature (Jan–Aug 21): Australia 0.67 °C above average| Australia coolest Jan–Aug since 2012Rainfall and maximum temperatures
Recent conditions (last 3 months)
Rainfall deciles: Maximum temperature deciles:
June – August 2021 June – August 2021
• Rainfall (Jun–Aug 21): Aust 4% below average (wettest since 2016) | No states/territories in top/bottom 10
• Max. temperature (Jun–Aug 21): Aust 1.27 °C above average, 7th highest on record | Qld 4th highest, NT
5th highest, Tas & SA both 9th highestRainfall and maximum temperatures
Recent conditions (last month)
Rainfall deciles: Maximum temperature deciles:
August 2021 August 2021
• Rainfall (Aug 2021): Aust 39% below average | No states/territories in highest/lowest 10 on record
• Maximum temperature (Aug 2021): Aust 1.77 °C above average, equal 9th highest on record | Qld 5th
highest, WA 10th highestRainfall deficiencies
17-months 48-months
April 2020 – August 2021 September 2017 – August 2021
• Short-term deficiencies (since February 2021) have been alleviated due to near-average rainfall in 2021.
• Medium-term deficiencies (since April 2020) are most notable in eastern Queensland.
• Long-term deficiencies (since September 2017) persist across several regions, with greatest deficiencies in
eastern South Australia, northern Victoria, western New South Wales, southern Western Australia, south-
eastern Queensland, and the northern Murray-Darling BasinRoot zone soil moisture
Recent conditions (0–100 cm below surface)
Very much above
average
Above average
Average
Below average
Very much below
average
August 2021 July 2021
• Soil moisture in July was above average in eastern NSW and southern Qld, southern parts of WA, SA and
Victoria, and western Tasmania
• Soil moisture in August has recently decreased across much of the mainland, particularly away from far
southern locationsForest Fire Danger Index (FFDI)
July 2021
August 2021
June 2021Trends in extremes
• Extreme heat
Coastal erosion
• Fire weather
• Tropical cyclones
36Trends in extreme heat • Extreme heat days: recent trend shows increased likelihood • 43 extreme heat days in 2019 is highest on record • La Niña in 2020–21 likely contributed to reduced number of extreme heat days in 2020
Trends in coastal erosion and inundation
• Global sea level has risen by around 25 cm since 1880; half of this rise has occurred since 1970
• Approximately 1 metre of horizontal incursion for every 1 cm of sea level rise
• Rates of sea level rise vary across the Australian region, with the largest increases to the north and south-
east of the Australian continentTrends in dangerous fire weather days
• There has been an increase in the annual frequency of dangerous fire weather days across Australia
• Map shows the change in number of days that the FFDI exceeded 90th percentile, between two periods:
• July 1950 – June 1985
• July 1985 – June 2020Tropical cyclone numbers and IOD phase
During negative IOD years:
• Average to above-average TC seasons since 1970/71 were more likely during neutral or negative IOD years
• In the 8 negative IOD years since 1970, the average date of the first tropical cyclone in the Australian region was around
3 weeks earlier than normal (mid-November compared to the normal date of early December)
• Long-term trend: steadily declining TC numbers across Australia—average since 1970 is 11, since 2000 the average is 9Tropical cyclone numbers and ENSO phase During La Niña years: • Average to above-average number of tropical cyclones since 1970/71 associated with La Niña or neutral-ENSO state • Only 3 seasons since 2000 have seen 11 or more TCs • The only time multiple severe tropical cyclones made landfall in Queensland was during a La Niña year • Long-term trend: steadily declining TC numbers across Australia—average since 1970 is 11, since 2000 the average is 9
Trends in tropical cyclones
Observed change in frequency of tropical cyclones
1980-2018
Sources: National Oceanic and Atmospheric Administration; Geophysical Fluid Dynamics Laboratory
• Red and orange areas show where tropical cyclone frequency has increased, while blue and green signifies
decreased frequency from 1980–2018
• There has been a downward trend in the number of tropical cyclones observed in the Australian region
since 1982. The trend in cyclone intensity is harder to quantify.http://bom.gov.au/knowyourweather
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