Amber heat health alerts have been issued by the UK Health Security Agency (UKHSA) with a potential heatwave set to develop to the south of the Humber this weekend.
Temperatures across North Yorkshire will not be as high as in London (31c) but forecasts say they will be between 23c and 27c.
The heat alerts could affect some rail routes to London, the South West and Midlands.
The amber level warnings cover the east, south-east and south-west of England as well as London, and are valid until 20:00 on Tuesday.
Yellow alerts are valid across the Midlands during the same period.
Amber heat health alerts are issued when high temperatures are likely to have a significant impact on health and social care services.
Cloud and showers will affect areas further north and west, with temperatures around 17-24C (63-75F), closer to the average for mid-June.
The forecast weather may cause trains to be disrupted. Heat can make overhead lines expand and sag, there can be line-side fires and also rails can buckle.
Advice for customers:
Please check before you travel and allow more time for your journey. Speed restrictions may be in place which can cause delays and cancellations.
Please also carry water with you – you can find water refill stations at all Network Rail managed stations and some other larger ones too.
If you feel unwell at the station, please don’t board a train, seek assistance from station staff or use the help point.
Further information can be found on the National Rail hot weather page.
