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Admiralbrücke in Berlin-Kreuzberg at the beginning of September: "It was quite dry in large parts of Germany, sometimes much too dry"

Photo: IMAGO/Emmanuele Contini

After a summer that was too warm in Germany, temperatures in September 2023 were also well above typical values for the month. According to a preliminary evaluation by the German Weather Service (DWD), the average temperature reached 17.2 degrees Celsius in that month, which is 3.9 degrees more than in the internationally valid reference period from 1961 to 1990. The DWD speaks of an "enormous meteorological anomalies". An above-average amount of sunshine contributes to this: 246 hours of sunshine so far – almost 65 percent more than in the reference period (150 hours).

DWD meteorologist Martin Jonas explains why it is still so warm in large parts of Europe and what experts expect for the coming days.

MIRROR: Meteorologically, the summer has been over since the end of August, it feels like we are still in the middle of it. Why is the warm weather so stubborn?

Jonas: Currently, several low-pressure systems are located over the North Atlantic or Northeast Atlantic and repeatedly shovel warm, subtropical air from the western Mediterranean, for example from the Iberian Peninsula and northwestern Africa. At the same time, the low-pressure systems block cooler, polar air masses from the north, so they do not reach us. As a result, we are currently experiencing temperatures above 20 degrees Celsius in Germany, and around 30 degrees Celsius in some regions, which is already exceptionally warm for the end of September.

MIRROR: How extraordinary, exactly?

Jonas: September is not quite over yet, but in all likelihood it is heading for a new record in terms of temperatures. By the end of the month, no temperature drop is expected that could jeopardize the record.

MIRROR: Were there any other special features in September?

Jonas: It was quite dry in large parts of Germany, sometimes much too dry. Only in the Alps were there almost average rainfall, which was also due to the fact that it rained very persistently there last week. In addition, it was quite humid in a strip from northern North Rhine-Westphalia, across Lower Saxony to Mecklenburg.

MIRROR: What is the situation in Europe?

Jonas: The whole region is characterized by the low-pressure systems over the Atlantic. In northwestern Europe, for example in Great Britain and Scandinavia, it is already quite autumnal. The temperatures there are around 15 degrees Celsius, 20 degrees are no longer reached there. In Eastern Europe it is still quite warm, in Moscow it is still about 24 degrees, in Ukraine it is about 25 to 30 degrees Celsius. In the Mediterranean region, too, temperatures are still around 30 degrees, in Spain even up to 35 degrees. It is still very summery there and it will stay that way for the time being.

MIRROR: Why are the low-pressure systems over the Atlantic so persistent at the moment?

Jonas: This is due to the pressure conditions above the ocean. In a way, the Atlantic Ocean is the weather kitchen of Europe. The so-called North Atlantic Oscillation pushes low-pressure systems from west to east towards Europe. It is driven by pressure differences between the Icelandic low in the north and the Azores high in the south. At the moment, however, there is a lack of thrust from the North Atlantic, and the lows are hardly moving from the spot.

MIRROR: Why do they draw warm air from the south to Europe and not cold air from the north?

Jonas: Low-pressure areas suck in air in an attempt to equalize pressure and cause it to circulate. At the same time, the rotation of the Earth ensures that this air rotates counterclockwise in the northern hemisphere. So if a low-pressure area is located northwest of us, as is currently the case, it sucks in air masses from the warm south and we get temperatures like those we have now measured. Only when the lows move further east towards Poland and the Baltic States, the current reverses in our country. Then we are on the back side of the low and it shovels cool air from the north over Europe to us counterclockwise. However, this is not in sight at the moment.

MIRROR: Is the warm September a consequence of climate change?

Jonas: Attribution research is concerned with estimating the influence of climate change on individual weather events. But that doesn't fall within my expertise.

MIRROR: When does the typical autumn weather come?

Jonas: At least it will get a little cooler in the coming days. The coldest day will be Saturday in the short term, when temperatures are in a range of about 17 to 23 degrees Celsius. After that, it should get warmer again, on Monday up to 27 or 28 degrees Celsius in the south, in the north it will remain around 20 degrees. On Wednesday there will probably be another small downward swing. The bottom line, however, is that it remains relatively warm. We are not approaching really autumnal temperatures in the medium term, i.e. in the next 10 days. In this respect, we are still a long way from the first frost.