Air Temperature

The abnormally warm weather which had set in the ETR in August remained warm in early September. The air temperatures averaged for the first decade of September exceeded the normal values by 2-5° or more. `New temperature maxima were observed in the Black Earth Region and in the south, in the Astrakhan and Rostov Regions, and in the Crimea. In the second decade, the anomalous heat solely survived in the south but also came to the far-eastern Kaliningrad Region where no such warmth in mid-September has ever been seen for more than 70 years. New daily temperature maxima were recorded there. As for the other regions of the ETR, the temperature conditions normalised, or even tended to negative anomalies in the Volga Region. But in the third decade, everything changed again. Almost the entire ETR fell under the spell of "Old Wives' summer," and the decade-averaged temperature anomalies reached +5° or more. New temperature maxima were recorded in the north-west of Russia at that time.
All September, extreme warmth dominated over the entire Arctic region of Russia. Again and again, unprecedented temperature maxima were recorded on Frantz Joseph Land, on Vize, Golomyanny and Kotelny Islands, on Cape Chelyuskin, in the Yamalo-Nenets Autonomous District, in Yakutia, in the Magadan Region and in the north of the Khabarovsk Territory. The temperatures in Eastern Siberia and in Yakutia were 2-6 or more degrees higher than usual.
Such temperature distribution during September produced above-normal monthly-averaged temperatures everywhere in Russia except for individual areas of the Kamchatka and Altai Territories. The anomalies exceeded +2° in most of the country, and +4-8° in the Arctic region. September 2020 became the warmest September in Russia since the beginning of regular meteorological observations in 1891, and surpassed the previous achievement of September 2016. Likewise, the Asian part of Russia and the territory of the Far East Federal District occupied the top warmest positions in their meteorological chronicles, and the monthly-averaged temperature in the Siberian Federal District was awarded Rank 2 among the highest values.
In the east of Eurasia, the weather was mostly warm in September. The monthly-averaged air temperatures in Mongolia, in the north of China and in Japan were 2-4 or more degrees higher than normal in some places. This September, a temperature above +40° was recorded for the first time on the Japanese island of Honshu. The monthly-averaged air temperatures in the southern and western regions of China and in the south of the Korean Peninsula were close to normal, or below normal in some places.
In the countries of South-East Asia, the monthly-averaged temperature was 1-2° higher than usual. Closely normal or slightly increased values were recorded in India and Pakistan.
Central Asia enjoyed coolness this September. There, the anomalies of the monthly-averaged temperatures were, if small, negative: down to -1°, as a rule.
Summer swelter persevered in the Near and Middle East: above +48° in Jordan, +47° in Kuwait, +46° in the north-eastern Turkey, +42° in Israel and +36° in Transcaucasia. The monthly-averaged air temperature in these regions was 2-5° above the normal value.
The air temperature in September averaged over the territory of North Africa duplicated the highest value set in 2002: 2-4° above the normal one in Algeria, Tunisia, Egypt and Sudan.
Most of September, Europe was basking in warmth of the Azores anticyclone. Thereby, the monthly-averaged temperature turned out to be above-normal all over the continent, most notably, 2-3° or higher than usual in Central and Eastern Europe. New temperature maxima were recorded in Germany, Italy, France, Latvia, Belarus, Cyprus and Ukraine. In Greece, the thermometer readings sometimes crossed the +30° mark even in the last days of September. September 2020 became the third warmest in the meteorological chronicle of the continent (in pair with September 2006). On the bottom line, the weather was even warmer in September 2011 and September 2016 only.
In most of the USA, the monthly-averaged air temperature was approximately normal, with the exception of some western states where searing heat was tantalizing California, Nevada and Arizona. Numerous air temperature maxima were recorded including an absolute temperature maximum of +49.4° in Los-Angeles. This September was the hottest in California and Nevada. The abnormal heat facilitated the development of natural fires. The abrupt Arctic invasion in the beginning of the month brought severe colds to the northern states of the country.
The monthly-averaged temperature was in general close to normal in most of Canada and Mexico. In the latter country, the weather in the north-west regions bordering California was warmer than usual, such as the weather in the north of the Arctic region in the former one.
This September was the second warmest in the history of meteorological observations in the Arctic since the record-breaking 2016. The anomalies of the monthly-averaged temperature exceeded +5-8° in the eastern (Eurasian) section, and +2-4° in the western (American) section. The smallest area of Arctic sea ice is normally observed in mid-September. This year, it became the second minimum; the ice cover was smaller in September 2012 only.
In September 2020, the monthly-averaged air temperature in the Northern Hemisphere matched the record-breaking value of September 2019 to an accuracy of 0.1°.
The average temperature of September in Moscow was +13.9°, implying an anomaly of +2.9°. This was the fourth highest result in the history of meteorological observations in the capital. The highest one, +14.9°, belongs to September 1938, and the second highest, to the XXI century. The average temperature in 2018 was +14.6°.

Ocean surface temperature

The surface temperature of the Pacific Ocean in the Northern Hemisphere was still very high, and its anomaly averaged over the entire Ocean surface reached +1°. This was the second largest value in the history of observations, less than the respective value as of September 2016 only. The average anomaly remained at a level of extreme values for the fourth month in succession. The monthly-averaged figures were above-normal almost over the entire surface of the Pacific. The anomalies exceeded +2° at temperate and northern latitudes. Negative values were only observed in the Yellow Sea, partially, in the Sea of Japan and the East China Sea, and, most importantly for future circulation, along the Equatorial Belt in the east of the Ocean: there, negative anomalies exceeded one degree in places. A new La Niña has started.
In the Atlantic Ocean, the average anomaly was the same as in August. The background of weak positive anomalies preserved in most of the Ocean. Large positive anomalies (+1…+2° or higher) formed off the northern coast of South America, along the Gulf Stream east of the US coast, in the Davis Strait and in the marginal European seas, namely, in the Mediterranean, Black, North and Baltic Seas.
Water was very warm all along the Northern Sea Route. The average SST values in the Kara Sea and the Laptev Sea were 4-5 or more degrees above their normal figures.


In the ETR, rains were rather rare in September: as a rule, their rate in the constituent entities of the Federation was less than normal, and the normal value was partially achieved in the north-west only. Still, occasional heavy showers did occur during the month. For example, they inundated the Krasnodar Territory in the first decade. More than 100 mm of atmospheric moisture could accumulate per day in some locations including Novorossiysk. Much less, but still a lot of precipitation – up to 40 mm per day – went at the same time to the Tver and Smolensk Regions, as well as to the Volga Region. A new daily maximum of precipitation was recorded in Samara. In the middle of the month, record-breaking precipitation of 30-50 mm of daily rainwater hit the northern and central regions of the country.
However, the main amounts of precipitation in September were allotted to the Asian territory of Russia. The normal monthly totals in the south of Siberia and of the Far East were exceeded by 1.5-2.5 times in certain places. Like in August, rains were abundant in the Trans-Baikal, in the Amur Region, and in the Jewish Autonomous, Khabarovsk and Primorye Territories. The daily amounts of rainwater topped 50 mm in places. In the Urals, heavy rains fell in the middle of September bringing up to 40 mm of rain, which is comparable to the normal monthly amount. Snowfalls now expanded from the north of Siberia to the south, viz., to the Altai Territory and the Baikal area. Snow banks up to half a metre high grew in the foothills.
In East Asia, typhoons brought a lot of precipitation. Its monthly totals in China and Mongolia were 2-3 or more times greater than usual in places. But cyclones were powerful enough to reach the western regions, so that a lack of precipitation amounting to less than 50% of the normal value was observed in the provinces of Xinjiang and Qinghai, and in the west of Mongolia. The rainwater amounts in Japan and Korea were either normal or slightly increased.
The situation was about the same in the countries of South-East Asia. Heavy downpours that took place on the islands of Java and Kalimantan in Indonesia caused floods that left thousands of people homeless, and claimed the lives of humans.
The Indian monsoon weakened, but was still strong enough to produce occasional heavy downpours on the Hindustan Peninsula where the normal precipitation amounts were exceeded by about 1.5 times in many regions. The rains caused floods and landslides in Pakistan and Nepal. The landslides blocked rivers; water overflowed the river banks and flooded huge areas of agricultural lands. The number of affected persons exceeded 20 million.
Almost no rains were observed in the Near and Middle East.
In Central Asia, dry weather in Turkmenistan and Uzbekistan was in contrast with abundant rains in Afghanistan, Tajikistan, Kyrgyzstan and Kazakhstan where up to 1.5-2.0 times the normal precipitation amounts were measured. Snow was falling in the east of Kazakhstan.
In North Africa, most precipitation fell along the Mediterranean coast, and from Senegal to Chad in the underside of Sahara. Floods occurred in Algeria and Tunisia where up to 40-60 mm of rainwater accumulated per day to create spates. Heavy rains in Senegal resulted in major flooding: there, more than 200 mm of precipitation was recorded for seven hours of continuous rainfall. Flash floods took place in Mauritania and Ghana as well. Niger was afflicted by new flooding: the water level in the same-named river rose by two metres above the critical mark, causing the water inrush to the nearest settlements, breaking through a local dam, and flooding thousands of hectares of agricultural lands. Incessant heavy rains created floods in Burkina Faso, Nigeria and Cape Verde. In the latter country, 80 mm of water fell from the sky in twelve hours.
In Europe, a strip-like precipitation pattern was observed. In Spain, the weather was dry in the south, but the normal precipitation amounts were exceeded by 1.5-2.0 times in the north and the centre of the country. In Madrid, 15 mm of rainwater, i.e., 40% of the monthly amount, fell for a single day. The conditions in France were opposite: dry weather in the north, and torrential rains in the south causing the most severe flooding. Up to four normal monthly amounts of precipitation were recorded for twelve hours in some regions. The weather being dry in Germany, Denmark and Switzerland, heavy rains that poured in Austria, the Czech Republic, Slovakia and Hungary measured in excess of the two normal monthly amounts. Snow that fell in the Austrian Alps and the north of Italy created snowdrifts up to 25-30 cm high. The ground near Rome was powdered by snow which has never been seen there before. Dry weather in the east and south-east of the continent defied the rains in Scandinavia and Greece with twice the normal monthly precipitation collected for a single day on Crete.
A lot of precipitation in September went to the east of the USA: 1.5-2.0 or more times the normal monthly amount in places. Heavy rains hit the states of Maryland and Virginia. A record-breaking amount of 79 mm fell in two hours in Washington, and up to 150 mm, in other parts of this state. On the other hand, almost no rains were observed in the west of the country. In California and Nevada, this September was the fourth driest in history. Forests continued burning due to intense heat and the lack of rains; the smoke from these fires reached the east coast and even spread to some countries of North Europe. This year, winter came early to the USA: snow already fell in Montana, Wyoming, Colorado, Nebraska and South Dakota. In some places, the snow depth reached 5-10 cm.
Heavy showers hit Mexico, Central America and the Caribbean countries. The flood water level on the Trinidad Island reached 1.5 m, resulting in flooding. In Canada, much precipitation, in excess of 1.5 times the normal monthly amount, was recorded in the east of the country (the province of Quebec), but almost no precipitation was observed in the west from the Yukon to Saskatchewan.
In Moscow, 65 mm of rainwater fell in September, which is exactly the normal amount. Let us remind that the normal annual precipitation total in the capital had already been acquired before the beginning of September.