Indian Summer UK Weather 2025: Definition, Forecast & Origins

Few weather terms grab British attention like “Indian summer” – that unexpected warm spell in autumn that makes you question whether summer really ended – but what actually qualifies as an Indian summer in the UK, and is 2025 shaping up to deliver one? The Met Office, the UK’s national weather service, has a specific definition that goes back more than a century.

Definition of Indian summer: Unseasonably warm, dry weather in autumn, typically October–November ·
Met Office criteria: At least 3 consecutive days of above-average temperatures ·
2025 forecast high: 25°C in southwest UK around September 8 ·
Historical UK maximum: 40.3°C recorded in July 2022 ·
Term origin: First recorded in 1778 by a missionary in Mohawk country ·
Alternative term: Second summer or old wives’ summer

Here is a summary of key facts about Indian summer in the UK:

What is classed as an Indian summer in the UK?

Met Office definition and criteria

• The Met Office Meteorological Glossary, first published in 1916, defines Indian summer as “a warm, calm spell of weather occurring in autumn, especially in October and November” (Met Office).
• It is not a formal meteorological term, but the Met Office applies a practical threshold: at least three consecutive days with temperatures above the seasonal average (Met Office).
• There is no statistical evidence that warm autumn spells recur at a fixed time each year (Met Office).

“Sometimes the rain is followed by an interval of calm and warm which is called the Indian summer.”

– J. Norton, letter from Mohawk country, 17 January 1778 (Met Office)

One important pattern: warm October spells can feel like a second summer, but the Met Office notes that before “Indian summer” became common in the UK, Europeans used variations of “Saint Martin’s summer” (around 11 November) (Met Office).

Difference from a standard warm spell

• A standard warm spell can occur in any season; an Indian summer is specifically an autumn warm spell after the first frost (where relevant) (Met Office).
• The Met Office hasn’t published a strict frost requirement, but the glossary’s “autumn” window sets it apart from summer heatwaves.
• Often associated with settled high‑pressure systems that trap mild air over the UK.

The implication: the Met Office’s definition provides a clear benchmark for when a warm autumn spell qualifies as an Indian summer.

Why is it so warm in October in the UK?

Meteorological drivers: jet stream and high pressure

• Stagnant high‑pressure systems can block Atlantic fronts, allowing warm air to build over the UK (Met Office).
• The jet stream often shifts north in early autumn, reducing the flow of cooler polar air.
• These setups can produce several days of unseasonably mild weather, especially in southern England.

Climate change and warmer autumns

• Average October temperatures in the UK have risen by about 1°C since the 1960s (Met Office).
• Spring 2025 was the UK’s warmest and sunniest on record (Met Office).
• June 2025 became the warmest June ever recorded in England and the second warmest for the UK in records since 1884 (Met Office).

Six facts, one pattern: the baseline is warming. A 1°C rise in autumn means that what was once a rare “Indian summer” could become a more regular October feature. The trade‑off is that the very phrase “Indian summer” may lose its exceptional meaning.

Has it ever hit 40 degrees in the UK?

Record UK temperature of 40.3°C in July 2022

• The UK recorded 40.3°C at Coningsby, Lincolnshire on 19 July 2022 (Met Office).
• That day broke the previous record of 38.7°C set in Cambridge in 2019.
• By contrast, Indian summer temperatures rarely exceed 25°C; the warmest October day on record is 29.9°C (1 October 2011, Gravesend) (Met Office).

Likelihood of 45°C in current climate

• The Met Office has said that 45°C is “possible” under current climate conditions, though still extremely rare (Met Office).
• January to June 2025 was the driest period for England since 1976 (Met Office), adding to drought risks that could amplify autumn temperature extremes.

“The Meteorological Glossary defines the phenomenon as ‘a warm, calm spell of weather occurring in autumn, especially in October and November’.”

– Met Office (UK national weather service)

What this means: 40°C days are summer heatwaves, not Indian summers, but both are influenced by warming.

What is the new term for Indian summer?

Why the term is considered offensive by some

• The phrase “Indian summer” has colonial origins, first recorded in 1778 by a Frenchman describing Mohawk country (Met Office).
• Some critics argue the label is derogatory because it stereotypes “Indian” (Native American) as “other” or “outside the norm”.
• A 2023 survey by Civic Journal (UK‑based weather explainers) noted that public awareness of the controversy is growing, though most Britons still use the term without offense.

Alternative names in modern usage

• “Second summer” – used descriptively in UK media.
• “Old wives’ summer” – a historic term, but rarely used today.
• Simply “warm autumn spell” – the Met Office often uses this neutral phrasing (Met Office).
• The BBC and Met Office still use “Indian summer” in forecasts but note sensitivities when questioned.

The implication: if you’re writing a weather report or a travel guide, “warm autumn spell” is the safe, inclusive choice. For historical or cultural contexts, acknowledging the origin debate gives readers the full picture.

What is the Indian summer UK weather forecast for 2025?

Long‑range outlook from the Met Office and BBC

• Early forecasts suggest a possible warm spell in early September 2025, with highs around 25°C in the southwest – possibly the first “Indian summer” candidate of the season (Met Office).
• The Met Office three‑month outlook for autumn 2025 indicates above‑average temperatures overall.
• Whether that warm spell meets the 3‑day threshold remains to be seen; forecasts beyond 10 days are uncertain.

“Spring 2025 was the UK’s warmest and sunniest on record, while June became the warmest June ever recorded in England.”

– Met Office (UK climate authority)

For travellers and event planners, the key takeaway is that autumn 2025 is likely to be warmer than average, increasing the chance of at least one “Indian summer”‑like spell. But the exact timing – whether September, October or November – is impossible to pin down more than two weeks out.

For UK residents and visitors alike, the choice is simple: keep an eye on the Met Office 10‑day forecast in late September and October. If you see three consecutive above‑average days, you’ll be living through what many still call an Indian summer – whether or not that label remains in common use a decade from now.

For anyone planning autumn activities in the UK, the pattern is clear: warmer autumns are becoming the new normal. The old phrase “Indian summer” may fade, but the experience of a golden, mild October week will likely become more frequent. For travellers and locals alike, the choice is to keep a weather app handy – and maybe enjoy a bonus beach day in October.