MAIN WEATHER AND CLIMATE TRAITS IN THE NORTHERN HEMISPHERE AS OF SEPTEMBER 2025

Air Temperature

With the beginning of September, summer returned to the ETR. In the first decade, average air temperatures became above-normal everywhere, 2-3° higher than normal in the north and west, as well as in the Caucasus. New temperature maxima were recorded in Karelia and Central Russia to exceed 30° in some places, and temperatures as high as that were measured in the Luhansk Region. In the second decade, temperature anomalies in the north and west of the ETR became even higher, reaching 4-6° or more degrees in the Russian North. New daily temperature highs were set in the Arkhangelsk and Murmansk Regions as well as in the Komi Republic. Meanwhile, temperatures in Central Russia returned to normal, while in some locations in the south, the average temperature for the second decade became even less than normal. In the third decade, no high positive temperature anomalies were detected in the ETR: the decade-averaged air temperatures were close to normal almost everywhere, or even sub-normal on the Black Sea coast of the Caucasus. In the last days of the month, frosts were observed, down to -7° in the south, and new daily temperature lows were set.

In the Urals, the weather remained warm until mid-month, with anomalies higher than 2-4° in the north. In the second decade, first frosts came there to the south, and in the third, record-breaking colds to the north.

The weather in Siberia kept up abnormally warm for almost the entire first decade; then, cold air masses started to dominate in the north, and warm ones, in the south. As a result, the average air temperature in the second and third decades in the north was 1-4 or more degrees below normal, whereas in the south, it was about the same value above that. At the end of the month, new temperature highs were set in the Omsk, Tomsk and Irkutsk Regions.

In the south of the Far East, air temperatures were above-normal for most of the month, while in its north, the cold in the first decade gave way to the warmth in the second and third ones. On the coast of the Sea of Okhotsk in Sakhalin, on the Kuril Islands, on Kamchatka, in Trans-Baikal and Primorye, new temperature maxima were recorded to reach or exceed 30° in some areas.

The average temperature of September 2025 in Russia was among the top ten highest in the 135-year history of regular meteorological observations; in the Russian North and the southern Far East, it was the third in the ranking list. Only Septembers 2023 and 2024 in the north or Septembers 2020 and 1959 in the south were even warmer. The monthly-averaged air temperature in most of Russia was above-normal, especially in the north and north-west of the ETR as well as in the south of the Far Eastern region where the normal monthly values were exceeded by 2-3° or more. The weather was notably colder in the north of Yakutia (with anomalies down to -2°) and slightly colder in some southern parts of the ETR.

In Moscow, the average air temperature in September was +13.8°, corresponding to an anomaly of +1.9°.

The weather in East Asia was extremely hot again: the average air temperature in the east of China, on the Korean Peninsula and in Japan was in excess of two or more degrees above normal. In China, this September was the second warmest in the history of observations, surpassed by September 2024 only. Even at the end of the month, the thermometer readings in the north of Japan rose to +30°.

The temperature patterns in the South-East Asian countries were roughly normal, but the monthly averages were, however slightly, above-normal.

The same can not be said about South Asia: indeed, while the monthly-averaged air temperature anomalies everywhere in Pakistan were weakly-positive, the weather in the south of India was typically slightly warmer than usual, but in the north and centre of the country, weakly-negative anomalies were observed.

Air temperatures in the Near and Middle East were close to normal; in Transcaucasia, the weather was somewhat colder than usual.

In most of Central Asia, temperatures were also normal, but in Kyrgyzstan and in some regions of Uzbekistan and Turkmenistan, this September was two or more degrees warmer than usual. In the north of Kazakhstan, the thermometer readings dropped to the record-breaking negative values at the end of the month.

Hot weather reigned in Northern and Eastern Europe where the normal monthly-averaged temperatures were exceeded by two or more degrees in Scandinavia and the Baltic, in Poland, Belarus, Ukraine, Slovakia, the Czech Republic, Hungary, Moldova and the Balkan countries. In Ukraine, the air would heat up above +30°: as reported, such heat at this time of year has not been seen for more than sixty years. The weather in Greece was even hotter; there, the temperatures reached +37°. On the contrary, coolness prevailed in the west of the continent – though, with new temperature highs on occasional days, as was the case in London.

This September in Canada was the second warmest on record, with only the previous September even warmer. The normal temperatures in the west of the country were exceeded by 2-4° or more. The average September temperature was two or more degrees higher than normal in the northern US along the Canadian border in the states of Washington, Idaho, Montana and North Dakota. But in the rest of the country, the temperature was normal.

In the Northern Hemisphere, this September was the second warmest in the meteorological chronicle since 1891, yielding to September 2023 only.

 

Sea Surface Temperature

 

For the seventeenth month in succession, a neutral phase of the Southern Oscillation was preserved in the equatorial Pacific. The average SST of the Pacific Ocean in the Northern Hemisphere reproduced its record-breaking value first set in 2016 and then regained twice, in 2023 and in 2024. The unprecedented monthly-averaged SST of the Pacific Ocean in the Northern Hemisphere was recoded continuously each month since October 2023 except for April 2025. This September, positive SST anomalies reaching +2…3° or more were measured in multiple water bodies at the northern, temperate and subtropical latitudes, and weakly-negative anomalies took place at the equatorial latitudes.

The average SST of the Atlantic Ocean in the Northern Hemisphere decreased compared to August, and was significantly lower than in September 2024 or 2023. Even though the SST was above-normal in most of the Ocean, anomalies can only be called high in the Caribbean Sea, in the Gulf of Mexico, off the coast of North America, as well as in Norwegian and Greenland Seas in the north. The SST of the Mediterranean Sea and the SST of the Arctic Ocean seas along the Northern Sea Route were remarkably greater than normal. Abnormally cold water was present at the temperate latitudes between North America and Europe.

 

Precipitation

 

Unlike in rainy August, dry weather prevailed this September in the ETR: the normal precipitation amounts were only reached in the Murmansk Region and the Yamal-Nenets Autonomous District in the north and in the South and North-Caucasian Federal Districts in the south. Moreover, the precipitation totals in the regions of the latter District were 2-3 times the normal values. Very heavy rains hit the North Caucasus several times during the month. At times, up to 50-100 mm of atmospheric moisture per day fell in Dagestan, Chechnya, Ingushetia, North Ossetia and the Krasnodar as well as Stavropol Territories. Heavy rains were also observed in the Murmansk Region where more than 60 mm of precipitation fell during two days in some places. The precipitation totals in the north-west of the ETR and in the Central and Volga regions did not exceed a half or, in some places, a quarter of the normal figure.

Normal precipitation was reached everywhere in the Urals Federal District save for the Khanty-Mansi Autonomous District. Heavy downpours notably raised the water levels in the Southern Urals and the Cis-Urals regions where more than 30 mm of precipitation accumulated per day in some locations.

Rains were heavy in Siberia; there, up to 30-50 mm of precipitation fell in one day in places, and new daily maxima of its totals were set, so that the normal amount was reached in most of the region, or exceeded by 1.5 to 2.0 times in Evenkiya and Altai.

In the Far East, precipitation was mostly normal, and was slightly above that only in the south of Khabarovsk Territory, in the Amur Region and on the Arctic coast. Heavy showers of intensity more than 25 mm/day fell on Sakhalin and the Kuril Islands.

Downpours continued pestering China where the normal precipitation values were exceeded by 1.5-3.0 or more times in the east and south of the country; roughly the same can be said about the north-western region. Particularly heavy rainfall was brought by Paraca super typhoon striking the provinces of Guangdong and Hainan, and attacking Hong Kong and Macau. Precipitation on the Korean Peninsula and in Japan was generally normal.

Heavy rains fell in the countries of South-East Asia, leading to massive floods in Indonesia and boosting the monthly precipitation totals to 1.5-2.0 or more times the normal quantity in that region.

Summer monsoon in India and eastern Pakistan was still vehement, raising the water levels in the rivers to unprecedented marks, and thereby leading to numerous floods. Monthly precipitation was 1.5-3.0 times above the normal figure.

The weather in the Near and Middle East was dry, rain falling in the Trans-Caucasus and in north-eastern Turkey only.

In most of Central Asia, the weather was dry alike. Rains fell mainly in Turkmenistan and in the northern regions of Uzbekistan, in monthly amounts 1.5 or more times exceeding the normal figure. Heavy snowfalls occurred in the north of Kazakhstan in the last days of the month, with a height of freshly fallen snow of up to 20 cm.

Dry weather was also observed in most of North Africa. Rains were only reported on the Mediterranean coast (in part) and in the Sahel region.

Central and Eastern Europe received normal amounts of rainwater in contrast to the south and south-east of the continent where they were virtually zero except for those brought by occasional heavy downpours. Indeed, in northern and southern Italy, e.g., in Lombardy and on Sicily, no such downpours have been seen for more than half a century. At the end of the month, heavy showers hit the regions in the south-west of Ukraine.

The weather in Canada was basically dry. In the US, rain fell in the west of the country and in the Rocky Mountains. Torrential rains caused floods in the east of Cuba. In Mexico, dry northern regions contrasted with rainy central and southern ones.

In Moscow, 9 mm of rainwater fell in September, which is 13% of the normal monthly figure. For the third time in a row, September in the capital was very dry, amounting to less than 20% of the total normal precipitation. September 2025 was the third driest in the meteorological annals of Moscow, after September 2023 with 8 mm of rainwater and record-breaking September 1949 with 7 mm.