Few UK towns get more days of 25 degrees or more than Merton
Winter’s chill peaks in January, at about 2.8°C (37°F) after dark. In January, nights here are milder than in 90% of UK towns. Rain peaks in October and eases off in March. Garden chairs stay out from May to September, the months with highs of 18–23°C.
Met Office 1991–2020 averages for the town itself.
A year in Merton at a glance
Each month’s typical high and low, in °C.
What a year in Merton feels like
Typical highs and lows by season and by month, from the Met Office’s 1991–2020 averages.
About 626 mm of rain a year
October is the wettest month and March the driest. About 14 days a year bring 10 mm (0.4 in) or more. 21st wettest of 33 London boroughs of 2,500+.
Rain by month
Millimetres
Sunshine by month
Hours of bright sunshine at Heathrow
30 air frosts and 26 days of 25°C a year
On about 30 nights a year the air drops below freezing, and on about under 1 days it stays below freezing all day. About 26 days a year reach 25°C (77°F).
Day counts are 1991–2020 averages from the Met Office’s 2 km grid. The Met Office calls a day of 25°C or more a summer day and a night below 0°C an air frost; ground frosts, on grass, come more often.
The Met Office station at Heathrow
Heathrow is 12 miles west of Merton, 25 m (82 ft) above sea level. It is the nearest of the 37 long-running stations the Met Office publishes in full.
| Month | High | Low | Rain | Air frosts | Sun (hours) |
|---|---|---|---|---|---|
| January | 8.4°C | 2.7°C | 59 mm | 6.8 | 59 |
| February | 9.0°C | 2.6°C | 45 mm | 6.2 | 76 |
| March | 11.7°C | 4.1°C | 39 mm | 3.0 | 120 |
| April | 15.0°C | 6.0°C | 42 mm | 0.8 | 169 |
| May | 18.4°C | 9.1°C | 46 mm | 0.0 | 197 |
| June | 21.6°C | 12.0°C | 47 mm | 0.0 | 197 |
| July | 23.9°C | 14.2°C | 46 mm | 0.0 | 206 |
| August | 23.4°C | 14.1°C | 54 mm | 0.0 | 192 |
| September | 20.2°C | 11.6°C | 50 mm | 0.0 | 150 |
| October | 15.8°C | 8.8°C | 65 mm | 0.3 | 111 |
| November | 11.5°C | 5.3°C | 67 mm | 2.7 | 68 |
| December | 8.8°C | 3.1°C | 57 mm | 7.2 | 53 |
| Year | 15.6°C | 7.8°C | 616 mm | 27 | 1,597 |
Met Office historic station data, Heathrow (London Airport), 1991–2020 months averaged (a month needs 20 of the 30 years; estimated values counted, missing months left out). Sunshine: Kipp & Zonen recorder.
How Merton compares
Against the 2,537 towns and cities of 2,500 or more across the UK, each with its own Met Office averages, and its place among London boroughs that size.
Nearby towns’ climate
The nearest towns of 1,000+ within 12 miles: a hill, a valley or the sea can make a real difference over a few miles.
| Town | July high | January low | Rain a year |
|---|---|---|---|
| Merton | 23.4°C | 2.8°C | 626 mm |
| Wandsworth 3.0 mi | 23.7°C about the same | 2.9°C about the same | 618 mm |
| Sutton 3.0 mi | 23.3°C about the same | 2.5°C about the same | 659 mm |
| Worcester Park and Stoneleigh 3.8 mi | 23.3°C about the same | 2.5°C about the same | 654 mm |
| Kingston upon Thames 4.1 mi | 23.5°C about the same | 2.6°C about the same | 633 mm |
| Lambeth 4.5 mi | 23.7°C about the same | 3.1°C about the same | 611 mm |
| Ewell 4.8 mi | 23.3°C about the same | 2.4°C about the same | 653 mm |
Merton weather by month
Average daily high and low, mean temperature and rain, 1991–2020, for the town itself (the Met Office’s HadUK-Grid).
| Month | High | Low | Mean | Rain |
|---|---|---|---|---|
| January | 8.4°C 47°F | 2.8°C 37°F | 5.6°C | 59 mm 2.3 in |
| February | 8.9°C 48°F | 2.7°C 37°F | 5.8°C | 44 mm 1.7 in |
| March | 11.6°C 53°F | 4.1°C 39°F | 7.9°C | 38 mm 1.5 in |
| April | 14.8°C 59°F | 5.7°C 42°F | 10.3°C | 43 mm 1.7 in |
| May | 18.1°C 65°F | 8.7°C 48°F | 13.4°C | 46 mm 1.8 in |
| June | 21.1°C 70°F | 11.6°C 53°F | 16.4°C | 49 mm 1.9 in |
| July | 23.4°C 74°F | 13.7°C 57°F | 18.6°C | 47 mm 1.9 in |
| August | 23.0°C 73°F | 13.6°C 56°F | 18.3°C | 56 mm 2.2 in |
| September | 20.0°C 68°F | 11.2°C 52°F | 15.6°C | 51 mm 2.0 in |
| October | 15.7°C 60°F | 8.5°C 47°F | 12.1°C | 67 mm 2.6 in |
| November | 11.4°C 53°F | 5.3°C 41°F | 8.4°C | 67 mm 2.6 in |
| December | 8.8°C 48°F | 3.1°C 38°F | 5.9°C | 60 mm 2.4 in |
| Year | 15.4°C | 7.6°C | 11.5°C | 626 mm |
Where Merton’s numbers come from
Averages over 30 years, not a forecast.
- Mean temperature, rain and day counts: HadUK-Grid 1991–2020 averages for the 7 Met Office 2 km grid squares whose centre lies inside Merton’s built-up area.
- Highs and lows: the Met Office publishes average daily maxima and minima on its 12 km grid; each is moved by the difference between the town’s 2 km mean temperature and the 12 km square’s, which carries the town’s own height and setting over.
- Weather station and sunshine: Met Office historic station data for Heathrow (London Airport), 12 miles away, months of 1991–2020 averaged.
- Comparisons: every town and city of 2,500 or more across the UK, all four nations, read the same way.
Met Office HadUK-Grid · Met Office Climate Data Portal · Historic station data. Open Government Licence v3.0.
Questions about Merton’s climate
How warm does Merton get in summer?
July is the warmest month, with average highs of 23.4°C (74°F). About 26 days a year reach 25°C (77°F), more than almost every UK town.
How cold does Merton get in winter?
February nights average 2.7°C (37°F). The air drops below freezing on about 30 nights a year, and about under 1 days a year stay below freezing all day.
How much rain does Merton get?
About 626 mm (25 in) a year, less than 87% of UK towns. October is the wettest month (67 mm) and March the driest (38 mm).
How sunny is it?
The nearest Met Office station with a sunshine record, Heathrow (12 miles away), averages 1,597 hours of bright sunshine a year. Sunshine isn’t on the town grid, so this is the station’s figure.
Where do these figures come from?
The Met Office’s HadUK-Grid 1991–2020 averages, which turn thousands of weather stations into a map of the UK in 2 km squares; the page reads the squares inside Merton. They are 30-year averages, not a forecast.
Contains Met Office data © Crown copyright 2026, Open Government Licence v3.0. HadUK-Grid 1991–2020 averages via the Met Office Climate Data Portal; station averages from Met Office historic station data. Today’s forecast for Merton →
Contains public sector information licensed under the Open Government Licence v3.0. Contains HM Land Registry data © Crown copyright and database right 2026. Contains OS data © Crown copyright and database right 2026 (ONS boundaries). Northern Ireland: Source: NISRA; contains Land & Property Services data and Ordnance Survey of Northern Ireland information, © Crown copyright, licensed under the Open Government Licence v3.0. Scotland: contains National Records of Scotland data, Registers of Scotland data and SEPA data, © Crown copyright / © SEPA 2025, licensed under the Open Government Licence v3.0.