Air temperature
At the beginning of the month, the weather in the ETR somewhat improved after the colds in the third decade of August: the temperatures approached the normal values or even noticeably exceeded them in the north where new daily maxima were set in the Murmansk and Arkhangelsk Regions, in the Nenets Autonomous District and Novaya Zemlya. The heat in the second decade spread further south and finally occupied the entire north-west of the country as well as Central Russia in part. The record-breaking maxima were now recorded in Karelia and in the Leningrad, Pskov, Kaliningrad, Moscow, Vladimir, Kostroma and some other Regions. But what happened in the third decade had never been observed this time of year before. The entire ETR and the Urals received much more heat than usual (with +2-6° anomalies), leading to record-breaking temperature maxima in many locations from the Baltic to the Urals, higher than +25° in places, and the air temperatures at the end of September matched those observed on a good summer day.
But beyond the Urals, cold days were more frequent. In Yakutia and in the north of the far East, negative anomalies of the decade-averaged temperatures reached -2…-3° and the thermometer readings could drop to -5…-10°, yet the abnormal heat would break through even there on occasional days: for example, the unprecedented temperature maxima were recorded at the beginning of the month in Trans-Baikal. At the end of September, heat came to Siberia, Yakutia and the south of the Far East, and new records of heat were established in Primorye, on Sakhalin and the Kuril Islands.
In final monthly-averaged terms, the weather was abnormally warm (with +2…+4° anomalies) in the north and centre of the ETR, in the Urals and in the south of Siberia, about normal almost everywhere in the rest of the country, and colder than normal in the central regions of the Khabarovsk Territory.
In the history of regular meteorological observations in Russia since 1891, this September was the third warmest in the country after September 2020 and September 2016, was the all-time warmest in the ETR as a whole and in the North-West Federal District separately, the second warmest in the Urals, and the fourth warmest in Central Russia, in the Volga region and over the entire Asian territory.
As in Russia, this month was abnormally warm in the countries of East Asia. In China, it was the warmest in the meteorological annals, with the monthly temperature 0.1° higher than the previous record-breaking one dated 2021. The weather in the central and north-eastern provinces of the country was significantly warmer than usual: there, the monthly-averaged temperature anomalies were +2° or larger, and the air temperature on some days exceeded +35° in certain locations. Yet the anomalies were even larger in Japan where they reached +4° or higher.
This September, the average air temperature in South-East and South Asia was close to normal everywhere except for the west of Pakistan where it was slightly above normal, and the thermometer readings rose above 40° on some days.
The picture in the countries of the Near and Middle East was similar: there, the weather was as hot as in summer. The temperatures in Saudi Arabia and Iraq hit +45°, and their monthly-averaged anomalies exceeded 2° in the south of Iran.
All over Central Asia, the monthly-averaged temperatures were close to normal, mostly against the background of weak positive anomalies save for the Aral Sea region in Kazakhstan where those anomalies were weakly negative. From time to time, summer heat invaded Tajikistan and boosted the temperature up to the record highs.
In North Africa, the monthly-averaged temperature was above normal, two or more degrees above in some places, and this September was the warmest in the history of meteorological observations.
Europe was basking in warmth all month. New temperature maxima were reported almost in all countries of the continent, and the monthly averages were 2-4 or more degrees higher than normal. The final overall figures showed that September 2023 was the warmest in the meteorological chronicle of the continent, and the previous achievement established in 2011 and reproduced in 2016 was exceeded by more than a degree.
The weather in all North America with the exception of Alaska was also abnormally warm. The record-breaking monthly-averaged temperature was reported in Canada where this September was deemed the warmest in history; in the US, it was the third warmest after 2019 and 2016. The unprecedented temperatures were recorded in Mexico and in the countries of South America where the monthly-averaged temperature anomalies were +2…4° or higher.
In the bottom line, this September in the Northern Hemisphere was the warmest since 1891.
This month had the same the same rank in Moscow where the previous record established in 1938 was exceeded by 0.1°.
 Sea Surface Temperature
El Niño continued to develop its strength at the eastern equatorial latitudes of the Pacific Ocean. Abnormally warm water was observed from the date line to the coasts of Central and South America, and the area of +2° or higher positive anomalies expanded dramatically. Such positive anomalies across the Mexican and US coasts merged with even higher positive SST ones at the moderate latitudes where they exceeded +2…4°.
This September, the surface of the Atlantic Ocean in the Northern Hemisphere was the warmest in the history of meteorological observations: the previous record high dated 2003 was topped by 0.3° right away. The monthly-averaged SST of the Atlantic Ocean in the Northern Hemisphere reached its absolute maximum for the ninth month in a row, so that new record achievements were sequentially established each month from January 2023 and on.
In the ETR, this September was dry, with the precipitation totals less than half their normal monthly amounts in most of the territory. The latter amounts were only reached in the north (in the Murmansk, Arkhangelsk and Leningrad Regions, in the Republic of Komi and in the Nenets Autonomous District) and in the south (in all constituent entities of the North-Caucasian Federal District, in the Astrakhan Region and in the Republic of Kalmykia), with the drought taking place in the South Federal District. Still, occasional heavy showers did occur: at the beginning of the month, they hit the Black Earth region, their intensity reaching 35 mm/day. New precipitation maximum was recorded in Saint-Petersburg. In the north, snow was observed as early as in the middle of September.
The trends in the Urals and to the east of them were different; there, the normal precipitation amounts were exceeded by 1.5-2.0 or more times (e.g., in the Chelyabinsk, Amur and Magadan Regions as well as in Taimyr, Altai, Tyva and Kamchatka). The record-breaking precipitation was observed in the Primorye, Amur River region, Trans-Baikal and Khabarovsk Territory. In some locations, the daily precipitation totals reached 30-60 mm.
In China, precipitation in September mostly went to coastlines and to the south-west of the country. The downpour which hit Hong Kong was the heaviest in history, and set a new maximum of hourly rainfall intensity. But the most dramatic precipitation figures were measured in the province of Sichuan where the rains resulted in floods, and the normal monthly precipitation was exceeded by 2-3 or more times. The weather in the north of the country was dry. The precipitation amounts in Japan and in the countries of the Korean Peninsula were about normal.
The precipitation totals in the South-East Asia were close to normal. Heavy rains inundated the Philippines including its capital Manila.
In India, the ending summer monsoon brought a lot of rains in quantities exceeding 100 mm of rainwater per two hours or 250 mm per day in places.
Rains in most of the Near and Middle East were scarce; their relatively large amounts fell in the Arabian Peninsula. Though, it should be kept in mind that the normal figures for these areas are very small, and a single heavy rain may result in a major increase of the monthly precipitation anomaly. At the beginning and the end of the month, rains descended upon Istanbul and caused massive floods there. Snow fell in the mountains of Azerbaijan.
In Central Asia, most rains went to the western regions of Kazakhstan where the normal monthly amounts were significantly exceeded in some places; the weather in the rest of the territory was dry.
In South Africa, rains fell southward of Sahara and along the Mediterranean coast. In Libya, they caused floods that killed thousands of people. The floodwater level reached three metres in certain places.
Europe was well-protected from rains by the Azores anticyclone; thus, the precipitation amounts were much less than normal. The exceptions were Spain with downpours causing rain floods at the beginning of the month, England with pelting rains in the south-west of the country in mid-September, and Greece with heavy showers arriving at the Aegean coast in the last days of the month. In the north, the precipitation amounts in the Scandinavian countries were normal.
Rains in Canada were very rare: only along the Atlantic coast of the country did they add up close to the normal monthly amount. In the USA, they passed along the same coast. At the end of the month, heavy rains deluged and paralysed New-York. They were so intensive that the normal monthly amount was achieved just in three hours. According to the meteorological service of the city, such rainfall intensity had been never observed before. A lot of precipitation went to the west of the country. The weather in Mexico and in the countries of Central America was dry.
This September, Moscow received just 8 mm of rainwater, amounting to 12% of the normal monthly figure. This September was the second driest in the meteorological annals of the capital. The precipitation total was even lower in September 1949 when 7 mm was measured.