Drought continues or worsens after dry September
Tue 8 Oct 2019

Last month was the tenth driest September in the past 120 years of reliable rainfall records across Australia. The 2¾ years from January 2017 to September 2019 are the driest in the record book in the last 120 years in the Murray-Darling Basin as well as for NSW overall.

September saw less than 20% of average rain across most of the country. BoM.

September again saw widespread failure of rain thanks to the most strongly positive Indian Ocean Dipole (IOD) in almost 20 years. In late September, the IOD weekly value hit an average of +1.76°, the highest since at least 2001. The IOD measures the difference in ocean temperature between the west and east tropical Indian Ocean. A strongly positive IOD shows waters to Australia's northwest are cool and produce less moisture to be carried across the continent as northwest rainbands.

September saw less than 20% of average rain across most of the country, the small exceptions being pockets of coastal SA, VIC and NSW. The TAS East Coast received a much-needed dowsing on 6-7 September. What appears to be a phenomenal rainfall streak from the Kimberley to around Alice Springs is something of an illusion - average rain there in September is minimal, so the 5 to 25mm received provided some stupendous if rather meaningless percentages. WA fared worst with the 5^th driest September on record while rain in the Murray-Darling Basin was the 9^th lowest. TAS did best, but was still 27% below average while VIC came second-best on 36% below.

The dry September made the nine months from January to September the 4^th lowest January to September average for all Australia in the 120-year record. Added to this were above average temperatures in September which made January to September the second warmest in the 110-year record. The resulting higher than normal evaporation means that root-zone continued below average into August, the last figures available, for most of Australia.

Rainfall deciles for the three years from 1 October 2016 to 30 September 2019. Almost all the Murray-Darling Basin lies in the bottom 10% of 3-yearly totals in the past 120 years while large areas of the basin in northern NSW and southern QLD are at record low levels. BoM.

The Monthly Drought Statement issued on Tuesday 8^th shows the Murray-Darling Basin as a whole has had record low rainfall in the 2¾ years from January 2017 to September 2019 with the worst impacts being in the northern MDB. Compared to the Bureau's standard 1961 to 1990 period, MDB overall has been 37% below average, the northern MDB 40% below average and the whole state of NSW not much better at 34% below average.

The Statement says "The deficiencies have been most extreme in the northern Murray–Darling Basin, especially in the northern half of New South Wales and adjacent southern Queensland, where areas of lowest on record rainfall extend from the Great Dividing Range west as far as Dubbo and Walgett. Some of the largest rainfall deficiencies have occurred in the upper catchments of some of the major tributaries of the Darling, including the Macquarie, the Namoi–Peel, the Gwydir, and the Border Rivers."

Because of the length of the drought, most dams on the tributaries that feed the Darling River are between 1 and 8% full, and flow in the rivers at most gauges, including the Darling, is down to a trickle or has ceased. The current percentages of full capacity in the largest dams are:

• Burrendong, Macquarie River (NSW): 4.4%
• Split Rock, Manilla > Namoi Rivers (NSW): 1.6%
• Keepit, Namoi River (NSW): 0.9%
• Copeton, Gwydir River (NSW): 8.5%
• Pindari, Severn River (NSW): 4.9%
• Beardmore, Balonne River (QLD): 4.7%
• Glenlyon, Pyke Creek > Dumaresq River (QLD): 3.6%

The Menindee Lakes are effectively empty with 0% in Lakes Menindee, Pamamaroo and Cawndilla and 5% in Lake Wetherell.

This is what most of the Darling River looks like now. The sentiments are food for thought and action. And in case you're wondering, Useless Loop on Heiresson Prong does exist.

 BoM's Heatwave Service recommences
Tue 1 Oct 2019.

With our rapid propulsion into summer, the Bureau's Heatwave Service, which is normally active from early spring to late autumn, was in use from day one. Heatwaves are defined as three or more days in a row when both daytime and nighttime temperatures are unusually high for a location.

The service provides a series of seven 3-day maps, two showing the current situation and five giving progressive 3-day forecasts showing heatwave location and severity across Australia. They are categorised as low-intensity, severe and extreme.

Early warning, especially of severe and extreme heatwave conditions, is important not only for bushfire and infrastructure management but also for vulnerable people such as the elderly, ill and very young who need to take special precautions. A recent survey found that since 1900 heatwaves have killed more people in Australia than all other natural hazards combined. An article by some of the survey team in The Conversation goes more briefly into the history of heatwaves and how not to lose your cool in one.

The Heatwave Service is available on the Bureau’s website.

WA: Storm causes damage, blackouts around perth. Fri 4 Oct 2019. A rapidly deepening low with a central pressure of 998hPa ploughed into the WA coast just south of Perth late Friday afternoon causing damage and downing powerlines, cutting power to over 25,000 premises. Ahead of the low, a front which crossed the area late morning also brought damaging winds. [Andrew Miskelly, ABC]

Record high wind gusts for October were recorded around mid-afternoon at six locations in the Perth area, the highest 107km/h on Rottnest Island. Heavy rain fell, mostly with the passage of the low across the state's South West. Several places in the Central Wheat Belt and along the South Coast recorded up to 16mm in an hour (see downpours), while general falls from the system around Perth, the South West and South Coast were between 25 and 40mm.

 SA, NSW: Early 40° days inflame the drought
Sun 6 Oct 2019.

The low pressure system that brought storms and gales to WA on Friday skirted the SA coast on Saturday 6^th and crossed TAS on Sunday, towing a weak cold front across SA, NSW and VIC. The front dragged the warmest air since autumn from central Australia into the southeastern states and brought strong winds that raised dust in parts of SA and NSW.

Temperatures in central SA on Saturday reached as high as 42.4° at Tarcoola and 41.8 at Port Augusta, with five towns on the Eyre Peninsula setting new October records. Cleve's top of 39.7° was its highest October temperature in 63 years of record-keeping.

On Sunday, temperatures were only slightly lower as the change, even weaker as its parent low slid SE over TAS, brought the highest temperatures to western and central parts of NSW. Bourke Airport recorded a top of 40.1 but exceptionally high temps for October were recorded in the Central West and on the South West Slopes and Monaro. Orange Airport, Forbes, Young, Cootamundra, Temora and Bombala AWS all set new October records, and most of those stations have been operating for about 25 years. The change and nearby low gave strong wind gusts along the VIC coast, with 107km/h at Aireys Inlet and 83km/h at Orbost also new October records. Wilsons Promontory had a breezy 126km/h.

The early-season heat is bad news for farmers and wildlife alike. Aerial electromagnetic surveys funded by the NSW Government have begun in western parts of the NSW Central West searching for groundwater to provide drinking water for communities at risk of running dry. In SA, ecologists say that waterholes previously thought to be permanent are drying up resulting in mass die-off of wildlife both large and small, with the deaths of millions of kangaroos most noticeable. [ABC]

As the second summer's heat and drought begin to bite, University of New South Wales ecologist Katherine Moseby told ABC News "We were seeing them going into the public toilets and eating toilet paper. We're even witnessing them eating the stomachs of dead kangaroos on the side of the road, trying to get some nutrition out of the corpses. It was really quite upsetting and quite horrible to watch."

 Hot and dry to the end of 2019, but hope is on the horizon
Thu 26 Sep 2019

The BoM's Climate Outlook was issued this afternoon with heat and little prospect of rain in most parts of the country, but a ray of hope towards the end.

For October to December it's expected to be drier than average for much of Australia apart from the northern half of WA, where decent falls from wet season buildup thunderstorms are likely from November. Daytime temperatures are very likely to be warmer than average across the whole country with only the western half of TAS seeing cooler conditions. The situation is more complex for overnight temperatures, with warmer than average minima expected over WA and in a band from the QLD Gulf Country to the NSW coast, but cooler than average temps in the southeast, along the QLD coast and in the NE Top End.

The main climatic drivers behind the BoM's reasoning are that a positive Indian Ocean Dipole (IOD) will persist for a few months, pushing rain-producing influences well west of the country. Meanwhile a negative Southern Annular Mode (SAM) will continue to bring Southern Ocean low pressure systems closer to southern Australia, with approaching fronts that drag hot, dry inland air southeastwards ahead of them. So it's a double-whammy of no moisture from the Indian Ocean and frontal changes across the south of the continent that produce heat ahead and little rain behind.

The interesting feature of the Outlook is the new forward view into January 2020 which shows up in 3-month expectations for November to January. If you compare the Oct-Dec to Nov-Jan outlooks, you can see the breakdown of the IOD beginning. In Nov-Jan, most of the continent north of a line from Perth to Townsville is likely to have median rainfall, and a little more in northern WA. That suggests January is likely to see good rains across the tropical north after a late-breaking wet season. Below that line, the likelihood of below average rain are still below median, but not as dire as in the Oct-Dec quarter suggesting improved rainfall generally during January.

Comparing Oct-Dec to Nov-Jan temperatures to gauge the impact of January on quarterly figures, daytime temps continue with a high probability of being above average across the continent, but become close to median in the Kimberley, NT and far NW QLD. That is because of the wetter conditions in this area. By the Nov-Jan quarter, minimum temps have warmed compared to Oct - Dec, indicating business as usual in January with warmer nights in the southeast and on the QLD coast, and significantly warmer nights in the NT Top End. The moister air accompanying rain can be thanked for these.

The Outlook is here and the video Outlook is here.

For those in the tropics, the Weekly Tropical Note issued on Tuesday says "A marked increase in humidity and the first thunderstorms for several months across the Top End of the Northern Territory and northern Western Australia hint at the start of the transition from the dry season to the northern wet season, which officially commences 1 October." Given the forecast late start to the true wet season, it remains to be seen how long the stormy buildup lasts, but on average the onset of the wet in Darwin is in the last week of December.

A notable tropical event has been a mid-level trough crossing central Australia early in the week which gave 10 to 30mm of rain to large parts of the southern NT and eastern Kimberley. Parts of these areas have not seen any rain in three months.

BoM issues Special Climate Statement on NSW/QLD fires. Thu 26 Sep 2019. The BoM has issued one of its detailed analyses on the weather surrounding the disastrous fires in SE QLD and NE NSW in the first half of September. All the ingredients of the worst fire weather were present: high temperatures, very low humidity, gusty winds and, for some locations, the driest January to August period on record resulting in a buildup of tinder-dry fuel. The SCS is here (pdf), and a list of all the BoM's interesting SCS reports is here.

New buoys measure Australia's wildest seas
Tue 24 Sep 2019.

The BoM recently replaced two of its ocean wave-monitoring buoys in the Southern Ocean. The buoys, which are exposed to the full force of the Roaring Forties, lie 10km W of Cape Sorell on Tasmania's West Coast and 7km W of Cape du Couedic at the SW tip of Kangaroo Island, SA.

The new Triaxis wave buoys have the ability to record wave direction as well as height and other parameters, and you can see them in green on the links above. The long-standing Cape Sorell buoy replaces one installed by the Bureau in January 1998 which in turn followed wave-monitoring on Tasmania's West Coast by the CSIRO. It's thought the highest wave recorded by the BoM's earlier Cape Sorell buoy was 18.4m on 16 September 2010 which was reported in The Age^‡, complete with a tram for comparison. A reported 19.5m wave in 2006 has been dismissed as an error. The higher 19.83m wave recorded on 29 July 1985 was measured by the CSIRO buoy.

The two buoys are in a select company of Southern Hemisphere wave-measuring buoys monitoring Southern Ocean wave physics in the world's stormiest and least studied waters. The highest wave measured in the Southern Ocean was 22.03m south of TAS in 2012 until that record was broken by a Triaxis buoy moored off Campbell Island by New Zealand's MetOcean in 2018. Only 4 months after deployment, it measured a massive 23.8m wave on 8 May 2018. For comparison, here is the 24.38m monster off Nazaré, Portugal, that put Brazil's Rodrigo Koxa into the record books for the highest officially-measured wave ever surfed. It's important to note, though, that open ocean waves can't be compared with waves breaking on a shore. As a wave approaches a shoreline, it moves into shallower and shallower water, and the energy that's been propelling the wave forward has nowhere to go but up and the wave grows taller as a result.

For some interesting comparisons with Northern Hemisphere waves in the Atlantic Ocean, you may find this 2017 AWN Blog an interesting read. The highest scientifically recorded North Atlantic wave has been 29.1m from trough to crest. it also discusses the fascinating rogue waves, where sequences of waves align to produce one or more waves that can be twice or more the height of their neighbours. The highest measured one was the famous Draupner wave which was measured at 25.9m as it swept under Draupner E oil platform in the North Sea. All these are pussies, though, compared to the rockfall-generated tsunami that tore down Lituya Bay, Alaska, following an earthquake late in the evening of 9 July 1958. The wave this created sloshed up the steep sides of the bay removing all trees and vegetation to heights of up to 524m above sea level. The event is covered in detail, complete with an eyewitness account, in this Wikipedia article.

  An unusually warm night in SE Australia
Sat 21 Sep 2019

Overnight Friday into Saturday 20/21 Sep was an unusually warm night given that it came in the NW stream ahead of a pretty inconsequential cool change.

Sixteen new provisional September high minimum temperatures were set stretching from the NSW Central West Plains to the TAS East Coast. All except three of them are from AWSs with short 15 to 25 year histories. Lake Cargelligo Airport, with a 50-year history, added a remarkable 3.0° to its previous record while Essendon Airport in Melbourne's north, also with a half-century history, added just 0.1°. Rutherglen Research is the outstanding one, though. Daily records there go back to 1912 providing 101 complete years of observations. Saturday morning's minimum of 18.7 breaks the previous September record of 17.8 set on 28 Sep 1928, so a significantly warm September night in the vineyards. The full list of new records is here.

One of the great pities of the shift to Automatic Weather Stations in Australia during the 1990s and 2000s has been the loss of continuity with older, often very long records at most locations across the country. AWSs have been put in places where there weren't manual stations previously, or have been moved to a location not comparable with the old manual station. Forbes, Cowra and Young are classic examples where the manual station was in town (usually at the Post Office), with records back to 1873, 1907 and 1907 respectively, while the AWS is in a different environment at the airport 5 to 10km out of town.

Of course, the AWS era has led to huge improvements in monitoring the weather with readings taken as often as every minute and usually of a higher quality than in the manual observer era. However, although airports are better, more representative, locations for measuring most weather elements now due to urbanisation of the earlier station areas, it still makes meaningful comparisons with significant events more than a quarter of a century ago difficult.

Haiti: heavy rain brings flooding. Sat 21 Sep 2019 Heavy rain on Haiti, off the eastern tip of Cuba, has caused severe flooding with 2 deaths and 4 missing reported so far. 300 houses are flooded, 30 destroyed and 55 damaged while there has been significant damage to infrastructure and agriculture. [Reliefweb]

Vietnam, Laos, Cambodia, Thailand: tropical storms bring flooding in Southeast Asia. Fri 20 Sep 2019 These four countries have suffered flooding following the passages of Tropical Storm Podul and Tropical Depression Kajiki earlier this month. As of 11 September, 10 deaths had been reported in Vietnam with 12,150 buildings damaged. In Laos, 14 deaths and 1 missing were reported with 102,000 people displaced while in Thailand there were at least 33 deaths, over 4,300 buildings damaged and 325,000ha of crops under water.

On 20 September over 87,000 families had been affected in Cambodia in continuing flooding with 10,000 evacuated and 12 deaths. [The Watchers, Reliefweb]

USA: Tropical Storm Imelda brings heavy rain, tornadoes and flash flooding to Texas. Fri 20 Sep 2019 Tropical Storm Imelda crossed the Texas coast near Freeport around midday local time Tuesday 17^th. Though sustained winds were only around 65km/h, coastal areas S and SW of Houston saw up to 406mm of rain following landfall as well as a tornado in eastern Houston and widespread flash flooding. As of the 20^th, 2 deaths had been reported and 6 were missing in rising creeks and bayous and on flooded roads.

In Houston, many schools and the George Bush Intercontinental Airport were closed and all public transport shut down. Flooding was felt on the coast at Galveston and east to the Louisiana border. A state of disaster was declared in 13 counties in SE Texas as the remnants of Imelda continued to move inland bearing heavy rain. [VoA, Floodwatch, Reliefweb)

Atlantic & Pacific Cyclones: The Americas beset by tropical activity. Wed 18 Sep 2019 As the Northern Hemisphere tropical cyclone season gets into full stride, this NOAA image via the UK Met Office shows six tropical storms or cyclones in a favoured belt either side of Central and southern North America. Kiko and Mario are heading west into the North Pacific; Tropical Storm Lorena, soon to develop into cyclone strength, brushes up the west coast of Mexico; Tropical Storm Imelda has just crossed the Texas coast; major Tropical Cyclone Humberto heads into the Atlantic and is about to side-swipe Bermuda only a week after the north of the country was devastated by TC Dorian; and Tropical Storm Jerry is moving into the Caribbean to provide the next threat.

 Global wildfires: perceptions vs realities
Sat 21 Sep 2019

Wildfires burning in the Amazon Basin and Indonesia as well as an unprecedented early and disastrous start to our Australian southern fire season has again focussed attention on their negative impacts.

The total number of wildfires globally is enormous. 18,959,413 fires have been detected for the year to today according to Global Forest Watch Fires (GFWF) based on data from the MODIS and higher resolution VIIRS satellites. This is their map showing fires burning in the last day. As is normal, the greatest number lie in the tropical band across central Africa, especially the Congo, Angola and Zambia. Africa accounts for around 70% of global fires annually. 

Russia, driven by the fires in Siberia, comes second in number of fire alerts this year, Brazil third and Australia fourth, with most fires in the NT and WA. Indonesia doesn't appear in the year-to-date top ten, yet, because it has only been in the past month that the worst fires since 2015 have burned for agricultural clearing in Sumatra and additionally escaped into peatlands in Kalimantan. [Guardian, NOAA, NASA]

Global fire season comparison, 2001 to 2019, using MODIS data only (therefore fewer fires identified than when combined with VIIRS data). GFWF

It's interesting to compare global fire seasons using satellite data between 2003 and 2019. The lowest two lines, for 2001 and 2002, can be ignored as those were years that government agencies were setting up to use MODIS as a tool for identifying fires and issuing alerts. The remaining 17 years cluster far more closely together than you'd expect, showing that fires globally are a common and steady phenomenon, not varying greatly in number from year to year. Comparing years to today's date, 2019 sits at 12th out of 17 — so below average — in terms of number of fires identified.

While many developed nations, eastern Australia, western USA and southern Europe in particular, regard fire as an enemy, for much of the world's population it has long been a part of life and an indispensable agricultural tool to clear land or nourish the soil. Lightning from dry thunderstorms has started fires in grasslands and forests for aeons before humans arrived, so many ecosystems are dependent on regular burning to maintain their biodiversity and natural habitats.

It's surprising to learn that, despite global heating, the area burnt globally by fires, as distinct from the number of fires, has decreased by 25% since 2003 according to Yale Environment based on NASA data. This study in Nature Geoscience went much further back and examined charcoal records in sediments over the past 2,000 years. It concluded that global burning has dropped sharply since about 1870, and attributed that to the global expansion of intensive grazing and agriculture and improvements in fire management.

The increasingly apocalyptic reporting of fires is driven by their increased intensity helped by global heating as well as urban sprawl that sees increasing settlement in forest and grassland areas on the edges of cities and in regional areas. However, it is more complex than that. This detailed study by Doerr and Santin, published by the Royal Society, explains the paradox of why we see wildfires as an increasingly severe problem while the evidence says that the global area burned has declined in the past few decades. It is a compelling read and brings some balance to many exaggerated wildfire perceptions.