When does summer 2023 start? Dates of new season, when was summer solstice, and what is longest day of year

Summer is finally here - and the UK has been basking in warm weather for the majority of June. There was joy as temperatures reached 30c, but also concern about global warming as it was revealed that the start of the month was the hottest first few days of June on record. The intense heat also led to thunderstorms across the country. But, it seems the heatwave is here to stay - whether we like it or not.

So, when exactly did summer start, when will it end, and what weather can we expect during this summer? Here’s everything you need to know.

When did summer begin?

There are actually two ways of calculating the first day of summer, depending on whether you follow the meteorological or definitions of the seasons. But, whichever one you follow, both are happening now. Meteorological summer began first, beginning on Thursday 1 June, followed by astronomical summer which began on Wednesday 21 June.

What’s the difference between meteorological summer and astronomical summer?

These are the key differences between meteorological summer and astronomical summer, and how the date of each is determined.

Meteorological summer

The meteorological summer date is the easiest to work out. It is based on the simple principle that the year is split into four seasons, and that each of these seasons are made up of three full months, as per the Gregorian calendar.

This definition makes it easier to compare seasonal and monthly statistics, and means that every season starts on the same date every year. This means that every year summer begins on 1 June and lasts until 31 August, with autumn then starting on 1 September.

Astronomical summer

The astronomical season is less straightforward to work out as it can change every year. This is because it starts on the date of the summer solstice, which comes later in June but can vary slightly from year on year.

In 2023, the summer solstice falls on Wednesday 21 June, which happens to be the same date as last year. It can, however, occur on any date between 20 and 22 of the month, although 21 June is the most common date for it to occur. The astronomical summer then lasts until another changeable date, the autumnal equinox - which this year lands on Saturday 23 September.

What is the summer solstice?

The summer solstice marks the date of the longest period of daylight and the shortest night of the year. For this reason, the summer solstice is also known as the longest day. This occurs when the Earth’s north pole has its maximum tilt towards the sun.

As well as marking the beginning of astronomical summer, the solstice can also be known as midsummer. This can be confusing, but it is because the days begin to get shorter after it has passed.

What is the autumn equinox?

Equinoxes take their name from the Latin for equal night. They happen twice a year, at the start of spring and autumn, and mark the moment the Earth’s equator passes directly through the centre of the sun’s path.

On each of these days, the planet should get 12 hours of daylight and 12 hours of darkness, although this is complicated somewhat  by the Earth’s atmosphere and weather conditions affecting the way we see sunlight. The autumn equinox can occur at any time between 21 and 24 September, and marks the start of autumn - if you follow the astrological definitions of the seasons.

When will summer end?

There are also two ways of calculating the last day of summer. According to the metrological measure of the seasons, the last day of summer this year will be Thursday 31 August, with autumn then starting on Friday 1 September. But, the astrological measure of the seasons states that the last day of summer 2023 will be Friday 22 September, followed by the first day of autumn on Saturday 23 September.

What does the long term forecast look like?

The Met Office has also published a three-month outlook for June to August 2023. The three-month outlook hints that there could be some hope for good weather during the bank holiday weekend, and also the weeks that follow.

 The current outlook for June, July and August gives a 45% chance of the season will be hot, with a 50% chance it will be near average for the time of year in terms of temperature. There's also a a 65% chance of near average rainfall, with a 15% chance of a dry season. 

A Met Office spokesperson said: "The elevated risk of a warmer than average summer this year, is consistent with wider global warming trends and the UK’s warming climate, after all, four of the five warmest summers on record for England have occurred since 2003. Nevertheless, looking at the figures you can see a near average summer is also still a possibility.   

"Whilst there are no strong signals for rainfall this summer, whatever the outcome, figures for the UK as a whole can hide big regional variations. Therefore, even if rainfall turns out to be near average for the country overall, we could still see some localised impacts from heavy rainfall or regional droughts."