NOAA weather watch 2017: Australian summer starts early

Most Australians were again reaching for the short sleeves earlier than normal.

The nation’s September 2017 mean was above average at +1.25°C and the 11th highest in the books for the start of the Southern Hemisphere spring, according to data from the National Oceanic and Atmospheric Administration (NOAA) in the US, the world’s leading weather and oceanic information agency.

A new September record was set on the 22nd when the national area-averaged maximum temperature rose to 33.47°C, shattering the previous record set on September 30, 1998 by 0.08°C.

All Australian states had above-average conditions, with the exception of Tasmania which had its 20th coldest mean temperature on record at 0.68°C below the 1961–1990 average.

By spring’s end in Australia, the line between the seasons was hazier than ever, with a national mean temperature of 1.13°C above the 1961–1990 average and the sixth highest on record. Queensland, NSW, Victoria, Western Australia, and Tasmania had a top 10 warm September–November period, with Tasmania, after a slow start, notching its highest spring temperature.

All regions except South Australia and the Northern Territory observed mean temperatures for the season amongst the 10 warmest on record. Both maximum and minimum temperatures were above to very much above average over the majority of Australia.

Since 1994, a cooler than average spring mean temperature for Australia has been observed in only two years.

The average global land and ocean temperature for September was 0.78°C higher than the 20th century average of 15.0°C. This was the fourth highest September temperature on record, behind 2015 (+0.93°C), 2016 (+0.88°C), and 2014 (+0.79°C).

The Southern Hemisphere spring also got off to warmer start at sea – the average global ocean surface temperature was 0.63°C above the 20th century average of 16.2°C, the fourth highest September temperature in the 138-year record, behind 2015 (+0.83°C), 2014 (+0.75°C), and 2016 (+0.74°C).

The combined average temperature over global land and ocean surfaces for October was 0.73°C above the 20th century average of 14.0°C. This value tied with 2003 as the fourth highest October mark, behind 2015 (+1.0°C), 2014 (+0.79°C), and 2016 (+0.74°C).

Across Australia in October, the temperature was 1.42°C above the 1961–1990 average and the 10th highest for the month.

Queensland, NSW, Victoria, and Tasmania had a top nine warm October. NSW had the largest positive temperature departure from average at +2.16°C and the fourth highest for the state.

The trend continued in November with Australia’s mean temperature 0.70°C above average, the 18th warmest in the last 108 years.

Tasmania and Victoria had their highest and second highest November on record, respectively. Western Australia had its ninth warmest.

Globally, the NOAA’s January–November period was the third hottest 11-month stretch in the 138-year record for the world’s land and ocean surfaces, with an average temperature that was 0.84°C above the 20th century average of 14.0°C.

Concerns for the Antarctic sea ice extent were also at an all-time high in many scientific circles by the end of spring. The coverage was just 15 million square km, which was 900,000 square km, or 5.66 percent, below the 1981-2010 average. This was the second smallest November Southern Hemisphere sea ice extent on record, only the November sea ice extent in 2016 was smaller.

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