Hot and thundery summer?

Despite summer 2023 being very mixed, with long periods of unsettled weather, it turned out to be warmer than average. Since then temperatures have mostly been above the long term norm and computer models are suggesting that it will continue to be the case in the coming months. Therefore, could 2024 deliver a classic summer to the UK?
Sunset in Christchurch
A fine sunset in summer 2023 but the season was very mixed
8th April 2024

Since last summer there have been frequent periods of unsettled weather. In fact, data from the Met Office shows that England has experienced its wettest 18 months since records began in 1836. The jet stream has often tracked further south than is typical, deepening areas of low pressure and directing them towards the UK. 

However, there are tentative indications of a transition to a more settled period of weather during the middle of April. Expected changes to the El Niño Southern Oscillation (ENSO) may also have an impact heading through the rest of the year, although correlations with the UK's weather are weak, particularly during the summer months. 

Despite the very wet conditions there has only been one month out of the last thirty one, December 2023 which recorded a Central England Temperature (CET) below the 1961-90 average. Therefore, the statistics taken on their own suggest the chance of a cool summer is low.

Seasonal models favour summer warmth

Seasonal models are run by a number of national forecasting systems. They provide indications of global trends for the coming months, but their skill level (accuracy) for the UK is still low. Nonetheless, they are a good starting point when considering the prospects.

The table below summarises the output from a number of the main seasonal models. They generally update monthly, so significant changes are possible before the meteorological summer begins.

Model Temperature Rain
GloSea (UKM) Above average No strong signal. Weakly below average in the far south and above it in the far north
ECM Above average Above average in the north
ECC Above average in the north Above average in the south
Meteo France Above average Above average in the far north
DWD Above average  Slightly above average
CS3 Above average No anomaly shown
JMA Above average Below average in the south and east
CMCC Above average Below average in the south
CFSv2 Above average Below average in the east
Table 1: Forecast temperature and precipitation anomalies, June, July and August


The notable things are:

i) All of the models favour above average temperatures in most of the UK when taken over June, July and August as a whole

ii) The rain signal is very mixed and uncertain

Anomalies don't give the full picture

When considering a three month period it is important to realise the anomalies may not provide the complete picture. For example, very wet periods could offset very dry ones, leading to average amounts of rain. However, this may be less the case for temperatures because as already noted, cool months have been the exception rather than the norm in recent years. 

ENSO forecast indicates change

The state of the El Niño Southern Oscillation (ENSO) has significant impact on temperature and rainfall patterns around the globe. Nonetheless its link to the UK summer is weak.

Latest forecasts suggest an 83% chance of a transition from El Niño to ENSO-neutral before the start of the summer. There is a 62% chance of La Niña developing through June to August. Although the link between La Niña and the UK's summer weather isn't considered strong, it could have some indirect impacts. For example, it may lead to temporarily lower global temperatures. It could also encourage an active Atlantic Hurricane season. 

Hurricane season "extremely active"?

Colorado State University's (CSU) prediction is for an "extremely active" hurricane season in 2024. They are suggesting that the combination of La Niña and an anomalously warm Atlantic Ocean will lead to the most active season since they started making forecasts in 1995. However, as with all forecasts there is a significant degree of uncertainty.

Accuweather is also predicting the possibility of a "super-charged" hurricane season and even suggests that forecasters may run out of names for storms.

Would a very active Atlantic hurricane season lead to a washout summer in the UK? Not necessarily. It is possible that ex-hurricanes in the North Atlantic could increase the chance of blocking areas of high pressure developing over Europe. The combination could increase the chance of periods of very hot weather affecting the UK and other parts of western Europe.

The anomalously warm Sea Surface Temperatures (SSTs) in much of the Atlantic also support the idea of higher than normal temperatures in the UK.

Sunny weather by the sea
Sunshine and sand, near Christchurch in Dorset 

Extreme heat becoming more frequent

In recent decades periods of extreme heat have become more frequent in the UK. Summer 1976 is often used as a  benchmark because the dry and hot weather continued for such a long time. However, the highest temperature recorded then, 35.9C in Cheltenham on 3rd July, has been surpassed easily a number of times in recent years. In fact, it was beaten by a huge 4.4C in 2022 when 40C was exceeded for the first time on record in the UK. 

Maximum temperatures for recent years are listed below:

2023: 33.2C, 9th September, Kew Gardens

2022: 40.3C, 19th July, Coningsby, Lincolnshire

2021: 32.2C, 21st July, Heathrow, Middlesex

2020: 37.8C, 31st July, Heathrow, Middlesex

2019: 38.7C, 25th July, Cambridge Botanical Gardens

2018: 35.3C, 26th July, Faversham, Kent

2017: 34.5C, 21st June, Heathrow, Middlesex

2016: 34.4C, 13th September, Gravesend, Kent (Note: This was in the meteorological autumn)

2015: 36.7C, 1st July, Heathrow, Middlesex

The last time 30C wasn't reached in the UK was in 1993. In that year the top temperature recorded was 29.7C in East Bergholt, Suffolk. In more recent times, 2007 and 2008 brought maximums of 30.1C and 30.2C respectively.

Recent climatology continues to favour above average temperatures and suggests an increased chance, relative to the norm, of hot spells in the summer months.  

Very hot periods this summer?

1) Seasonal models forecast above average temperatures over the June, July and August period as a whole

2) A transition to La Niña conditions suggests temporarily lower global temperatures

3) Forecasts for the 2024 Atlantic Hurricane season indicate high activity

4) Recent climatology continues to favour warm weather

Therefore, at this stage a warmer than average summer looks likely. The signal for rain amounts is much less clear. On balance, a very warm summer with an increased chance of stormy interludes is favoured.

An update will be issued in mid-May, with the final forecast being made available for the start of the meteorological summer on 1st June.

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