Summer 2024 potentially very warm?

The first look at the summer weather prospects was published on 8th April. It suggested a warmer than average season with an increased chance of stormy interludes was favoured. Is that still looking likely?

Since the first update temperatures in the UK have been mixed. The second half of April brought notably cooler conditions, but they weren't enough to offset the warm start. Average temperatures for the month finished above the 1961-90 norm. The first third of May has also been significantly warmer than the norm.

Therefore, out of the last thirty two months, only December 2023 recorded a Central England Temperature (CET) below the 1961-90 average. Recent climatology continues to suggest the chance of a cool summer is low.

Do seasonal models still favour 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.

The notable things are:

i) There is a strong signal for above average temperatures in most of the UK over June, July and August as a whole.

ii) The rain signal is mixed and uncertain. However, since the previous update the balance has tipped away from a wetter than average scenario towards a drier one.

The CFS forecast chart above is for July 2024. The yellow shading covering the UK is indicating higher than average pressure, which brings an increased chance of dry and warm periods. 

ENSO forecast changes

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

Latest forecasts suggest a 49% chance of La Niña developing through June to August. This is down from a 63% chance in the previous update. Although the link between La Niña and the UK's summer weather isn't considered strong, it could have indirect impacts. For example, it may lead to temporarily lower global temperatures. Also, there is a view that it has been associated with very wet summers. Therefore, if it develops later in the year than was previously expected it could offer support for a drier summer. 

Hurricane season "extremely active"?

Colorado State University's (CSU) forecast is for an "extremely active" hurricane season in 2024, with Accuweather predicting the possibility of a "super-charged" hurricane season. ECMWF has now also issued its outlook, suggesting 23 named storms and 13 hurricanes will develop between June and November. This also suggests a very active season.

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.

Hot periods this summer?

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

2) The chance of a transition to La Niña conditions is now lower than it was when the first update was published in April. This may suggest an increased chance of higher temperatures and lower rainfall totals

3) Forecasts for the 2024 Atlantic Hurricane season continue to indicate very 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 still much less clear. On balance, a very warm summer with lengthy dry periods is favoured.

The forecast for the meteorological summer will be issued on 1st June.

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