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Marine climate bulletin - August 2016

HadSST3 - map of anomalies in August 2016

Ocean climate summary for August 2016.

The global average sea-surface temperature for August 2016 was 0.66 ± 0.08°C above the 1961-1990 average according to the HadSST3 data set. For the global oceans, August 2016 was the joint warmest August on record together with 2014 and 2015. Each of these three Augusts was warmer than any previous August by a clear margin. Sea-surface temperature anomalies in the eastern tropical Pacific continued to decline through August, but more slowly than they did in the first half of the year. ENSO conditions remain near neutral.

Unusually-high SSTs - where temperatures exceeded the 90th percentile of the 1961-1990 climatology period - were widespread. The western and northern edges of the Pacific were unusually warm, with an area between the Philippines and Japan exceeding the 98th percentile. Areas of the Indian Ocean were also unusually warm, although extreme anomalies were less widespread than earlier in the year. In the North Atlantic, unusual warmth extended from the tropics and Gulf of Mexico, up through the western North Atlantic (where temperatures exceeded the 98th percentile over large areas) and across to Iceland. In the South Atlantic, tropical and eastern areas were unusually warm. Some areas of the equatorial Pacific were actually cooler than the 10th percentile. However, off-equatorial SSTs in the tropical Pacific exceeded the 90th percentile, with the more significant anomalies to the north of the equator. Other areas of unusually cold waters included an area off the coast of Argentina - where temperatures over land have been below the long-term average for several months - to the south of Australia and in the North Pacific. Large areas of the Southern Ocean were also colder than average, but the significance of the anomalies is difficult to assess as there are relatively few historical measurements from this area.

One notable difference from a year ago is that the large area of colder-than-average waters to the south of Iceland and the west of the UK that was present in 2015 was not so clearly visible at the surface in August 2016. However, analysis of the deeper layers of the ocean shows that a volume of cooler than average water remains beneath a relatively shallow warm surface layer.

The distinctive "horseshoe" pattern of colder-than-average waters in the central North Pacific, surrounded by warmer-than-average waters which has been in evidence for over a year was still discernible in August, but, as in July, an area of near-average or below-average SSTs extended to the west coast of the US. The horseshoe pattern is a feature of both El Niño and the positive phase of the Pacific Decadal Oscillation. The Indian Ocean Dipole which was strongly negative in July remained weakly negative in August. The negative IOD is characterised by lower SST anomalies in the west and higher SST anomalies in the east.

Based on data from the National Snow and Ice Data Center, Northern hemisphere (Arctic) sea ice extent was 5.6 million square kilometres. August 2016 was nominally the 4th least extensive August on record. Southern hemisphere sea ice extent was 18.19 million square kilometres. August 2016 was nominally the 18th most extensive August on record. For a more comprehensive review of conditions in the Arctic see Current Arctic sea ice extent - updated August 2016.

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