May was warmer than average for most places of the UK. At the beginning of the month an unsettled westerly regime brought rain south-eastwards. Thereafter, temperatures and sunshine increased. The early-May Bank Holiday was the warmest since its introduction in 1978. Despite cooler temperatures, the second week remained dry and sunny for many parts. The second half of the month was dominated by high pressure and easterly winds bringing warm air and sunshine. However, it stayed cooler and cloudier along the east coast. Rain and thunderstorms occurred during the last week with higher intensities in central and southern areas.
The UK mean temperature for the month of May was 11.9 °C, which was 1.5 °C above the long-term reference period 1981-2010. Overall rainfall was 64 % of average, but areas in central and southern England experienced close to normal rainfall. Sunshine 132 % of average. It appeared to be the sunniest May in a series since 1929.
UK Weather Averages: May 2018 (Source: Met Office)