September Weather Forecast: Is Another UK Heatwave On The Way?

Unseasonably high temperatures are forecast to sweep across much of England and Wales this week, with conditions expected to meet official heatwave criteria by midweek.

Warm air is building over much of the UK due to high pressure and a southerly airflow. On Monday, central and southern England saw temperatures climb above 30°C, with patchy rain and humid conditions reported across several region. London remained warm but did not reach the anticipated mid-30s, though further rises are still expected on Tuesday. These levels meet the Met Office's official heatwave criteria, which requires threshold temperatures to be exceeded for three consecutive days.

In response, the UK Health Security Agency has issued Yellow and Amber Heat Health Alerts for England. These warnings are directed at the health and social care sectors, highlighting increased risks to vulnerable groups.

Night-time temperatures are also expected to remain high in the southeast. In some areas, nights may not drop below 20°C, creating the conditions for what is known as a tropical night.

Storms, Showers, and Regional Shifts

While the heat will dominate headlines, showers and storms remain in the forecast. On Monday evening, some parts of southern and western England experienced patchy rain and light thundery showers, which spread sporadically north and east overnight. However, many areas remained dry.

Later in the week, particularly on Wednesday and Thursday, the risk of thundery outbreaks increases. This could bring more widespread rain to northwest England, parts of Wales, and Scotland.

Despite this brief unsettled spell, the weekend is likely to see the return of dry conditions, with high pressure regaining control. Isolated thunderstorms may still occur, especially in the south, but much of the country is expected to see warm, settled weather.

Will It Be a Heatwave or Indian Summer?

The rise in temperature has prompted queries about a possible Indian summer. While some media reports are using the term, the current forecast does not meet the traditional definition. An Indian summer usually refers to a warm spell later in the autumn, typically after the first frost, often occuring in October or November.

Meteorologically, summer has ended, and autumn has begun, but this week's weather does not yet match the conditions seen in past Indian summers. Temperatures will increase but are unlikely to rival the record levels experienced in previous years.

In September 2023, for example, the UK experienced its longest September heatwave on record. That period saw seven consecutive days of 30°C or higher, peaking at 33.5°C in Faversham, Kent, on 10 September. The hottest September day on record remains 35.6°C, recorded on 2 September 1906 in Bawtry, South Yorkshire.

Heat Alerts and Health Precautions

The issued heat health alerts highlight potential risks, especially for older adults, infants, and those with existing health conditions. Health services are being advised to prepare for a higher volume of heat-related cases.

With the warmest days expected early in the week and continuing warmth in the southeast later on, residents are being urged to stay hydrated and avoid strenuous activity during the hottest part of the day. Warm overnight conditions may also affect sleep and increase heat stress, particularly in urban areas.

Looking Ahead to the Weekend

By Sunday, much of England and Wales will see temperatures rise again, with 25-26°C likely in the southeast. While this is above the seasonal average of 17-22°C, it is not expected to reach the extreme levels seen in past years.

There is no indication of a named storm forming in the near term. Though low pressure on Wednesday could bring wet and windy conditions, it is not currently strong enough to be classified as Storm Amy.

As the weekend approaches, high pressure is forecast to re-establish over the UK. This means a return to mostly dry conditions with variable cloud and sunny spells, continuing the trend of warm September weather.