September 2017 Global Climate Report

September 2017 Selected Climate
Anomalies and Events Map

Introduction

Temperature anomalies and percentiles are shown on the gridded maps below. The anomaly map on the left is a product of a merged land surface temperature (Global Historical Climatology Network, GHCN) and sea surface temperature (ERSST.v4) anomaly analysis as described in Huang et al. (2016). Temperature anomalies for land and ocean are analyzed separately and then merged to form the global analysis. For more information, please visit NCEI's Global Surface Temperature Anomalies page. The percentile map on the right provides additional information by placing the temperature anomaly observed for a specific place and time period into historical perspective, showing how the most current month, season or year compares with the past.

Temperatures

In the atmosphere, 500-millibar height pressure anomalies correlate well with temperatures at the Earth's surface. The average position of the upper-level ridges of high pressure and troughs of low pressure—depicted by positive and negative 500-millibar height anomalies on the September 2017 map—is generally reflected by areas of positive and negative temperature anomalies at the surface, respectively.

September

September 2017 Blended Land and Sea Surface
Temperature Anomalies in degrees Celsius

September 2017 Blended Land and Sea Surface
Temperature Percentiles

Warmer-than-average conditions engulfed much of the world's land and ocean surfaces during September 2017, with record warmth observed across parts of central and southern Africa, southern Asia, and scattered across the western, northern, and southern Pacific Ocean, the Atlantic Ocean (specifically off the southeastern coast of South America), the Norwegian Sea, Greenland Sea, and Barents Sea, and across parts of the Indian Ocean. Near to cooler-than-average conditions across the globe were limited to western and central Russia, central Europe, the Sea of Okhotsk, the central and eastern tropical Pacific Ocean and along the western coast of South America, the northern Pacific Ocean, and across parts of western and eastern Indian Ocean. No land or ocean areas experienced record cold September temperatures.

Averaged as a whole, the global land and ocean temperature for September 2017 was 0.78°C (1.40°F) higher than the 20^th century average of 15.0°C (59.0°F). This was the fourth highest September temperature on record for the globe since records began in 1880, behind 2015 (+0.93°C / +1.67°F), 2016 (+0.88°C / +1.58°F), and 2014 (+0.79°C / +1.42°F). The 10 warmest Septembers have occurred during the 21^st century, specifically since 2003. September 2017 also marks the 41^st consecutive September and the 393^rd consecutive month with temperatures at least nominally above the 20^th century average.

The global land surface temperature was the third highest for September at 1.17°C (2.11°F) above the 20^th century average of 12.0°C (53.6°F), behind the record set in 2016, and 2015 (second highest). The 10 warmest Septembers have occurred during the 21^st century, specifically since 2005. This was the 24^th consecutive September and the 283^rd consecutive month with land temperatures at least nominally above the 20^th century average. Regionally, four of six continents had a top eight warm September temperature, with Africa having its warmest September since continental records began in 1910.

Select national information is highlighted below. Please note that different countries report anomalies with respect to different base periods. The information provided here is based directly upon these data:

• Australia's September 2017 mean temperature was above average at +1.25°C (+2.25°F) and the 11^th highest September in the nation's 108-year temperature record. All Australian states had above-average conditions, with the exception of Tasmania which had its 20^th coldest mean temperature on record at 0.68°C (1.22°F) below the 1961–1990 average. Queensland and New South Wales had a top nine warm September on record. The high mean temperature value across the nation was mainly driven by very warm maximum (daytime) temperatures—tying as the fifth highest September value for the nation as a whole since records began in 1910 at +2.03°C (+3.65°F). Regionally, Queensland had its second highest September maximum temperature at 2.85°C (5.13°F) above average, trailing behind the record set in 2013 (+4.12°C / +7.42°F). New South Wales had its sixth warmest September maximum temperature on record. Of note, a heat wave impacted the nation at the end of the month. Australia set a new record for the warmest September day on the 22^nd when the national area-averaged maximum temperature rose to 33.47°C (92.25°F), shattering the previous record set on 30 September 1998 by 0.08°C (0.14°F).
• Parts of central and northern Europe experienced near to cooler-than-average conditions during the month of September. Germany's September temperature was 0.7°C (1.26°F) below the 1981–2010 average, while the United Kingdom had a temperature departure of 0.1°C (0.2°F) below average. France, the Netherlands, and Ireland also had near to cooler-than-average conditions. Of note, the station located at Sherkin Island, Co Cork, Ireland had its coldest September since 2009. Austria had its coldest September since 2007, with a national temperature 1.7°C (3.1°F) below average; however, across the mountains it was the coldest September since 2001. In contrast, Tórshavn, the capital of the Faroe Islands, had a warmer-than-average September, with an average temperature of 11.0°C (51.8°F) or 1.4°C (2.5°F) above the 1981–2010 average. Europe, averaged as a whole, had its smallest September temperature departure from average since 2013 and the 19^th highest temperature since continental records began in 1910, with a temperature departure from average of 0.89°C (1.60°F) above the 1910–2000 average.
• Near to warmer-than-average conditions were observed across New Zealand during September 2017. The most notable temperatures (greater than +1.20°C / +2.16°F) were reported across Hawke's Bay, central Canterbury, and central Otago. The nationally-averaged September 2017 temperature was 11.2°C (52.2°F), which is 0.7°C (1.3°F) above average.
• Much of Canada had warmer- to much-warmer-than-average conditions during September 2017. According to Environment and Climate Change Canada, much of Ontario experienced temperatures that were 2.0°C–4.0°C (3.6°F–7.2°F) above average. The region was affected by a heat wave during September 23–27, bringing summer-like temperatures. Many locations reported temperatures above 30.0°C (86.0°F), with several locations setting new daily temperature records as temperatures soared between 10.0°C (18.0°F) and 14.0°C (25.2°F) above normal.
• The Kingdom of Bahrain's September 2017 mean temperature was the highest September mean temperature since national records began in 1902 at 34.6°C (94.3°F) or 2.2°C (4.0°F) above average. This value is only 0.01°C (0.02°F) higher than the previous record set in 1998 and again in 2015. The nation's maximum and minimum temperatures for the month were the highest (+2.6°C / +4.7°F) and third highest (tied with 2016; +2.3°C / +4.1°F), respectively, since 1946.

Across the oceans, the average global ocean surface temperature during September 2017 was 0.63°C (1.13°F) above the 20^th century average of 16.2°C (61.1°F)—the fourth highest September temperature in the 138-year record, behind 2015 (+0.83°C / +1.49°F), 2014 (+0.75°C / +1.35°F), and 2016 (+0.74°C / +1.33°F). Compared to previous monthly values, the September 2017 global ocean temperature was the lowest monthly temperature departure from average since December 2016. September 2017 also marks the 41^st consecutive September and the 492^nd consecutive month with ocean temperatures at least nominally above the 20^th century average. The last six Septembers (2012–2017) are the six warmest on record. Nine of the 10 warmest September global ocean temperatures occurred during the 21^st century (since 2003), with only one year from the 20^th century (1997) among the top 10.

ENSO-neutral conditions prevailed across the tropical Pacific Ocean during September 2017. According to NOAA's Climate Prediction Center, La Niña conditions are favored during the Northern Hemisphere fall and winter (Southern Hemisphere spring and summer) 2017–18. This forecast focuses on the ocean surface temperatures between 5°N and 5°S latitude and 170°W to 120°W longitude, called the Niño 3.4 region.

September Global Land and Ocean plot

September Global Hemisphere plot

The most current data can be accessed via the Global Surface Temperature Anomalies page.

Year-to-date (January–September)

January–September 2017 Blended Land and Sea Surface
Temperature Anomalies in degrees Celsius

January–September 2017 Blended Land and Sea Surface
Temperature Percentiles

The first nine months of the year have each ranked among the top four warmest months on record, giving way to the second highest January–September period in the 138-year record at 0.87°C (1.57°F) above the 20^th century average of 14.1°C (57.5°F), trailing behind the record year of 2016 by 0.13°C (0.23°F), but ahead of 2015 by 0.01°C (0.02°F). Nine of the 10 warmest January-September global land and ocean temperatures occurred during the 21^st century (since 2005), with only one year from the 20^th century (1998) among the top 10. Based on three simple scenarios, 2017 will likely end up among the top three warmest years on record.

Much of the world's land and ocean surfaces had warmer to much-warmer-than-average conditions during the first nine months of the year, with limited areas experiencing near to cooler-than-average conditions. Record warmth was observed across parts of eastern Asia, the western and central Pacific Ocean, western Indian Ocean, western Europe and surrounding oceans, and scattered across southern North America, southern South America, southern Africa, and Australia. No land or ocean areas experienced record cold September temperatures.

According to NCEI's Regional Analysis, all six continents had a top seven warm January–September period, with South America having its second highest September temperature on record, behind 2015. The global land surface temperature was 1.37°C (2.47°F) above the 20^th century average of 9.3°C (48.7°F) and the second highest value for the year-to-date, behind 2016 by 0.21°C (0.38°F). The global ocean surface temperature was the third highest such period at 0.68°C (1.22°F) above the 20^th century average of 16.1°C (61.1°F), behind 2016 (+0.79°C / +1.42°F) and 2015 (+0.70°C / +1.26°F).

January–September Global Land and Ocean plot

January–September Global Hemisphere plot

The most current data can be accessed via the Global Surface Temperature Anomalies page.

Precipitation

September

The maps below represent precipitation percent of normal (left, using a base period of 1961–1990) and precipitation percentiles (right, using the period of record) based on the GHCN dataset of land surface stations. As is typical, precipitation anomalies vary significantly around the world. September precipitation was generally drier than normal across parts of the eastern half of the contiguous U.S., northeastern Brazil as well as parts of southern South America, western and southeastern Europe, Australia, and scattered across western and southern Africa, and Asia. Wetter-than-normal conditions were notable across the western half of the contiguous U.S., northeastern Argentina, eastern Europe, Mongolia, and parts of south-central Russia.

September 2017 Land-Only Precipitation
Percent of Normal

September 2017 Land-Only Precipitation Percentiles

Select national information is highlighted below. (Please note that different countries report anomalies with respect to different base periods. The information provided here is based directly upon these data):

• Portugal experienced very hot temperatures that exacerbated the drought conditions across the nation. The much-drier-than-average conditions plagued Portugal during September 2017, resulting in the driest September in 87 years. As of September 30, 81.0% of the nation was in severe drought, while 7.4% was in extreme drought, according to the Portuguese Institute for Sea and Atmosphere. During the hydrological year (October 2016–September 2017), Portugal received a total of 621.8 mm (24.5 inches) of precipitation, which corresponds to 70% of normal precipitation and the ninth lowest total since national records began in 1931. Of note, the second half of the hydrological year (April–September) was extremely dry, ranking as the second driest on record, behind 2005.
• Denmark's precipitation total for September 2017 was 109 mm (4.3 inches)—the wettest September since 2001 (137 mm / 5.4 inches) and the wettest month for any month since December 2015.
• Much of New Zealand had above to much-above-average conditions during September 2017, with several locations setting monthly or daily rainfall records and near-records. Of note, Hanmer Forest reported a total of 126 mm (5.0 inches) in a 24-hour period on September 18—the highest one-day September rainfall since records began in 1905. South West Cape had its wettest September (163% of normal) since its records began in 1991.
• Below-average precipitation was observed across parts of northern and the southern half of Argentina during September 2017. However, parts of northeastern Argentina had above-average conditions, with several locations (Gualeguaychũ, Las Flores, and Azul) having their wettest September in the last decades.
• Much of Fiji continued to experience drier-than-average conditions, with over 70% of the stations experiencing below- to much-below-average conditions. According to Fiji's Meteorological Service, only six of 23 rainfall monitoring stations had near to above-average conditions.
• Australia as a whole had below-average precipitation at 66% of September normal precipitation total and the 35^th driest September in the 118-year record. Regionally, Queensland had its lowest September since 2003 and the tenth lowest in the record, receiving only 12% of its normal precipitation for the month. New South Wales had 14% of the month's total precipitation, resulting in the driest September on record.

Ocean Heat Content

Ocean Heat Content (OHC) is essential for understanding and modeling global climate since > 90% of excess heat in the Earth's system is absorbed by the ocean. Further, expansion due to increased ocean heat contributes to sea level rise. Change in OHC is calculated from the difference of observed temperature profiles from the long-term mean.

Ocean Heat Content (OHC) is essential for understanding and modeling global climate since > 90% of excess heat in the Earth's system is absorbed by the ocean. Further, expansion due to increased ocean heat contributes to sea level rise. Change in OHC is calculated from the difference of observed temperature profiles from the long-term mean.

Global OHC for July–September 2017 was the highest July–September OHC in our records, which extend back to 1955, although it is similar to the 2015 value. Overall, the latest OHC reveals widespread warmer than normal conditions, a situation observed since the last quarter of 2016. Much higher, > 20x10⁵ J/m³, than long-term mean OHC conditions are remarkable at northern high latitudes, i.e. in the Greenland Sea, Norwegian Sea, Barents Sea, and in Baffin Bay. Much higher than normal OHC is also observed in the Gulf Stream/North Atlantic Current, the Gulf of Mexico and the Caribbean Sea, the Agulhas Current and its retroflection. Cooler than normal conditions exist in the subpolar North Atlantic Ocean south of Greenland and Iceland, around the Equator in the central and western Pacific Ocean, in the western North Pacific Ocean, and along the Antarctic Circumpolar Current in the Indian Ocean sector.

References

• Peterson, T.C. and R.S. Vose, 1997: An Overview of the Global Historical Climatology Network Database. Bull. Amer. Meteorol. Soc., 78, 2837-2849.
• Huang, B., V.F. Banzon, E. Freeman, J. Lawrimore, W. Liu, T.C. Peterson, T.M. Smith, P.W. Thorne, S.D. Woodruff, and H-M. Zhang, 2016: Extended Reconstructed Sea Surface Temperature Version 4 (ERSST.v4). Part I: Upgrades and Intercomparisons. J. Climate, 28, 911-930.

Citing This Report

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