In the ETR, the weather was abnormally warm in the first decade of September only. From the Barents Sea to the Sea of Azov, the decade-averaged air temperatures exceeded the normal values by 3-4° or more. During this period, new daily maxima of temperatures were recorded in the Murmansk, Arkhangelsk, Vologda, Leningrad, Pskov, Yaroslavl, Moscow and Tula Regions as well as in the Republic of Karelia.
In the second decade, the anomalies subsided and the temperature background normalised in most of the ETR, whereas in the third decade, the colds suddenly arrived so that the resulting decade-averaged temperature amounted to 2-4° below the normal value. Absolute temperature minima were recorded in the Lower Volga Region, frosts came to Central Russia, and new record-breaking colds were observed in certain regions.
In overall, the temperature distribution in most of the ETR was close to normal in September. The Volga Federal District and partially the South Federal District were the only areas where the weather was noticeably colder than usual. Since the beginning of the century, such cold September in the former District was only observed in 2008. In the Orenburg Region, the monthly-averaged air temperature was two or more degrees below its normal value.


To the east of the Urals, the weather was unstable and frequently changing from warm to cold and vice versa. In the Trans-Baikal and in the south of the Far East, summer-like heat in the first decade gave way to bitter cold in the second one and changed to abnormal heat again in the third decade. In the Asian territory of Russia, the monthly-averaged temperature distribution was as normally observed there, with positive shifts of about 2° taking place only in certain Arctic regions (Taimyr, Chukotka and the Arctic archipelagos), in the Republic of Tyva, in the south of the Irkutsk Region, in the Republic of Buryatia and in the Trans-Baikal Territory. Regarding Russia as a whole, the average air temperature in September was 1° above the normal value. This is quite common; in this century, it has occurred for the tenth time already.
In East Asia, the air temperature remained high. In the east and north of China, in Japan and Korea, the monthly-averaged air temperature exceeded its normal value by 2-4°, while in Mongolia, by 4-6°. New temperature maxima were recorded now and then. In Japan, the thermometer readings could rise above +30…35°, as in summer. The heat continued to kill people: according to mass media reports, it has already claimed the lives of about 100 humans this year. In China, the monthly-averaged air temperature regained its second highest value in the meteorological chronicles: 2005 was the only year when September was even warmer – by 0.1°.
In South-East Asia, the monthly-averaged air temperatures matched the normal values. Though, it was excessively hot on some days. New positive temperature extremes were reported in Malaysia and Singapore.
In India, the sustained summer monsoon prevented solar heat from reaching the Earth surface. September was, if slightly, colder than usual there.
Hot summer weather persisted throughout the Near and Middle East where the average air temperatures exceeded the normal values by 2-4°, or by more degrees in places.
In North Africa, the air temperature was higher than normal as well, e.g., by 2-3° or more in certain areas of Algeria, Tunisia, Libya and Egypt.
In most of Central Africa, the temperatures were close to normal everywhere aside from the north of Kazakhstan where this September was colder than usual – by 2° or more in places.
In most European countries, the air temperature settled at its normal level after an abnormally hot summer. The only exceptions were observed in the south-east (Greece, Bulgaria, Romania and Moldova) and partially in Italy: even though no extraordinary temperatures were recorded there, the monthly averages still exceeded the normal figures by about 2°.
Last September was very hot in the USA. Its average temperature reached the record-breaking value observed in 2015. The normal air temperatures were exceeded by 2-4° in a vast territory from the Atlantic to the Rocky Mountains and the Gulf of Mexico. In the south, from Texas to Mississippi and from the Gulf of Mexico to Kansas, this September was warmest in the US meteorological chronicles. A large part of Mexico was also overtaken by abnormal heat. Yet Canada, the northern neighbour of the USA, basically received heat in normal amounts, in some places less as in Newfoundland and in some places more as in the Arctic zone.
In the Arctic, the third highest result was achieved for the monthly-averaged air temperature in September. Greenland, Alaska and the northern areas of Russia and Canada contributed about the same to this achievement (providing the anomalies of +2-4°). Only September 2012 and September 2016 were ever warmer in the Arctic.
This year, all three summer months in the Northern Hemisphere were the hottest in the history of regular meteorological observations on the planet, i.e., since 1891. The same happened in September with its monthly-averaged temperature reproducing the September outcomes in 2015 or 2016 to an accuracy of 0.1°.
In Moscow, the average air temperature in September was +12.3°, and the anomaly was +1.3°.
 

In September, the mean SST anomaly of the Pacific Ocean in the Northern Hemisphere slightly decreased as compared to the previous month (by 0.1°C) but still remained very high even if less than the record-breaking values obtained in 2015 and 2016. The abnormally high values of SST were observed in the eastern part of the Ocean from Central America to Alaska. There, the SST exceeded the normal value by 1-2° or more.
In the eastern part of equatorial latitudes, the anomalies were rapidly decreasing, and their negative values in some places reached 1° or more. Considering that the cold Peruvian current is intensifying, it can be expected that the neutral phase of the Southern Oscillation will not last long, and that a new La Nina will be established no later than the year ends.
In the Atlantic Ocean, the mean anomaly was much weaker. The temperature conditions close to normal ones were observed in most water areas. Water was colder than usual at equatorial latitudes, off the north-west coast of Africa and, quite traditionally already, to the east of Newfoundland and at the head of the Gulf Stream; conversely, water was warmer off the coast of the USA and Greenland. The water temperature was noticeably higher than normal in the marginal seas such as the Mediterranean, Black, North or Baltic Seas.
In the Arctic basin, the SST remained abnormally high and exhibited the anomalies of up to +4°. Still, these anomalies were less than in the previous month when they exceeded an unprecedented value of +5°.

In Russia, the precipitation totals in September were close to normal in most of the North-West Federal District but were steadily decreasing in a southward direction. The monthly totals in the Moscow, Lipetsk, Voronezh, Tambov and Kaluga Regions and in the north of the Volga Federal District hardly reached a half of the normal monthly amounts. Yet, in the south of the ETR, they became normal again, or even exceeded the normal value in places (in the Ingush Republic and the Republics of North Ossetia and Kalmykia). In the Urals, in most of Siberia and of the Far East, the precipitation amounts were either normal or increased. The precipitation was scarce in Chukotka, Sakhalin and the Primorye Territory only, but heavy rains observed there from time to time could result in up to 30 mm of atmospheric moisture per day. Heavy snowfalls that took place in Kuzbass and in the Far East created a fresh snow cover thicker than 10 cm.
In the central provinces of China, the amounts of rainwater were normal or increased, whereas in its eastern provinces and in Mongolia, less than normal. Tropical cyclones brought heavy rains to Japan and Korea.
The precipitation quantities were normal or increased in the entire South-East Asia excluding the northern regions of Vietnam and Laos.
The Indian monsoon in early summer looked weak, and many farmers were expecting a poor harvest ever since. However, heavy rains in August and September brought much more precipitation than usual, and the total amount of September rainfall on the Hindustan Peninsula exceeded the normal value by more than a third. Because of this, farmers were suffering from excess moisture. Flooding of large territories, casualties among the population and losses in livestock were reported. The September precipitation rates were exceeded all over India aside from its northern states of Punjab and Kashmir.
The weather remained dry in the Near and Middle East and in most of Central Asia excluding the northern territories of Kazakhstan.
In North Africa, many rains came to the countries of the Mediterranean coast (Algeria, Tunisia) and to those located southwards of the Sahara.
In Western and Central Europe, the weather was mostly dry. No September rains were to be seen in some regions of Italy. But the rainfall amounts in the east and north of the continent were normal or increased, with the monthly precipitation totals exceeding the normal values by 1.5-2.0 in some places in Slovakia, Czechia, Poland, Finland and the Great Britain.
A huge amount of precipitation (up to three or four times the normal monthly value) fell in the north of the USA and in the south of Canada. The monthly precipitation totals in the USA from Montana and Wyoming to the Great Lakes were among the first three highest values in the history of meteorological observations. The north-west states of the USA (Washington and Oregon) also received a lot of rain. Residents of the Canadian province of Alberta could observe an early snowfall. In the rest territories of these countries, the precipitation was scarce. For example, such a dry September has never been seen before in the south-east of the USA from Virginia to Alabama and Florida.
In Moscow, the monthly precipitation totals amounted to 29.0 mm, which is 45% of the normal monthly figure. In the 21st century, only September 2005 was even drier than this one.