It's that time of year once again, summer has arrived. I've had many of you in my inbox ask me for some insight, it is worth stressing these seasonal forecasts are somewhat experimental there is a whole new science which has emerged only in last 15 years. Also in the case of the UK, we are merely a grain of sand in the hemisphere, it is inherently tricky but as an informed weather nerd, this is my attempt.
Summer 2024 headlines:
Overall, a warmer-than-average summer is expected but it likely will not challenge the hottest summers of 2006, 2018 and 2022. I would not rule out very hot weather in excess of 38C (100F). I'd say this is most likely in the middle of summer in July, these past 12 months have been record-warm globally as such it is likely there will be intense hot air relatively close in Southern Europe.
Rainfall is a tricky one i'd say a wetter summer is more likely than a dry summer. I will outline why this is more probable if you continue reading. Separately, these past 18 months have been the wettest on record in England where we have experienced the highest level of rainfall since Met Office data began in 1836. In the midst of high global temperatures and record high sea surface temperatures even with onset of La Nina, which will begin the cooling influence of oceans and resulting atmospheric response, it will likely be too soon in terms of lowering temperature this summer in Northern Hemisphere.
El Nino transitioning to La Nina
Sea Surface Temperature (SSTs) Anomaly in the equatorial Pacific with blue areas indicating colder than average waters. This is not caused by weather but strengthening of easterly trade winds which results in cold water upwelling off the west coast of South America. We can see the development of La Nina well underway in the east of basin. Weak La Nina conditions are expected to develop by July this summer.
ENSO Pacific SST's anomalies as of June 1, 2024
Now the question might be how are "cool" ocean temperatures thousands of miles away is possibly influencing our weather? ENSO is one of the most important climate phenomena on Earth due to its ability to change global atmospheric circulation which changes the rainfall distribution around world. For NW Europe the effects are less obvious, in contrast to Australia the recent 2020-2023 La Nina event was marked by record breaking rainfall in eastern Australia as warm ocean water piles up in the western Pacific.
On average summers which are transitioning to La Nina as the first year are more prone to being shaken up by westerlies, while summer 2022 which featured 40C was a solidly La Nina summer this was during the 3rd consecutive year of La Nina. A very unusual setting this has only occurred two other times in the last 74 years. I think the oceanic/atmospheric link was stable and constant this is ideal and what you want to sustain fine and warm conditions for a significant period of time. This is very much unlike what we are seeing heading into summer 2024, where significant changes will be occurring from tropical forcing. We experienced the fifth strongest El Nino event in last 74 years over last winter, such a breakdown to moderately strong La Nina later in year within the same calender year is very unusual.
in terms of ENSO evolution this summer +ENSO to -ENSO the following analogues are most in line (1998, 2010 & 2016). This gives the following look for this coming summer. A low-pressure anomaly can be seen in Scandinavia this perhaps suggests the exceptional late spring warmth should be savoured here. Generally, it suggests a summer with increased northern blocking with winds coming more from a northern direction. It is a reasonable outcome for southern Britain but for Scotland, it is not pointing towards much of a summer but broadly across NW Europe it suggests near-normal temperatures perhaps slightly below.
Pacific Decadal Oscillation PDO
The PDO is a long-term climate pattern that affects temperatures of the Pacific Ocean over long periods it typically oscillates warm and cold every 10 years.
This summer the PDO is expected to be extremely negative the Eastern Pacific Ocean becomes cooler and the Western Pacific Ocean becomes warmer. Since, 1981 where these daily records have been kept only 2012 (remember the Jubilee washout?) as reached such a deeply negative phase. While this is more a variable in forecasting in US during -PDO summers we observe often are hot and dry in Europe but northwest Europe more prone to cooler and wetter. Of course, it is not black and white, 2022 was also deeply negative, however as previously discussed that summer coincided with a very unusual backdrop.
I compiled all known summers with strongly -PDO (1950, 1952, 1955, 1971, 1999, 2008, 2011, 2012, 2022, 2023) and the results are quite strongly favouring a deep low pressure anomaly in Atlantic Ocean within close proximity of Iberia, France, Ireland and southern UK. This might cause some concern, it does suggest a heightened chance of intense showers and thunderstorms. However, a stubborn low anomaly off NW Europe near to southwest is also associated with extreme heat in Western Europe. Low pressure drives up very hot southerlies from a very hot North Africa acting like a heat pump, this is part of the reason I believe this summer will see extreme heat spikes, but it will not persist for long periods at a time.
When we look at air temperature we get the following results... what we see there is no signal either way for the UK, but generally these summers are cooler than average in Northern Europe. We can identify a very hot North Africa, and this heat dome largely extends northeastwards into the Mediterranean region and SE Europe away from Western Europe. There is a lot to suggest this summer parts of Europe will experience a very harsh summer on top of existing warming trends Europe is warming twice the global average.
Warm Atlantic
Atlantic SST's as of May 31, 2024
As can be seen across the Atlantic warm anomalies are extensive and are in fact record breaking warm in the tropical Atlantic and Caribbean. It is no wonder a highly active hurricane season is expected in tandem with the developing La Nina which removes wind shear, therefore it is a more hospitable environment for developing tropical storms and hurricanes.
Last summer we also had a very warm Atlantic you might recall a "marine heatwave" around UK. The UK experienced its warmest June on record overtaking 1976 there's little doubt the warm ocean water will make it slightly warmer than it would be, and this is one of the main factors along with elevated global heating which quite strongly favours a warm summer. However, as ocean water warms more water evaporates in the air which results in more intense rain, this greater humidity is likely to be a feature this summer especially later on.
World Climate Service on Twitter (highly recommend a follow) tweeted the following:
“One of the more “interesting” analog signals in our recent summer forecast is the set of years with most similar N Atlantic SSTs. The pattern looks reminiscent of summer 2012 for Europe, although that year isn’t one of the analogs. Probably not what the UK crowd wants to hear.”
This is not what we want to hear in NW Europe, note the signal for a very warm and dry SE Europe once again - confidence is higher than average there. Overall, with the warm Atlantic you win and lose, as I feel last summer demonstrated well.
Solar Activity
I debated whether to include this but why not? It will not be given much consideration or any to the forecast. Summer 2024 finds itself during solar maximum a period of high solar activity, which is measured by the higher number of sunspots they appear darker because they are cooler than other parts of the Sun. We are at the height of the 11-year cycle this occurs due to changes in the Sun's magnetic field every many years it flips.
Current image of Sun's surface:
The sun is very spotty and restless at present activity is high. Sunspot 3697 is back facing the Earth it survived the rotation formerly known as 3664 which caused the exceptional low latitude aurora on night of May 10th, certainly a night that will be remembered for many years to come. It was even visible in central London although the phone camera did much of work. This summer there may well be further opportunity, the next solar max mid-2030s!
When we look at previous solar maximum summers back to NOAA records from 1948 we get the following look this combines (1958, 1968, 1979, 1989, 2001 & 2014). A rather bonkers extreme low-pressure anomaly in central-southeastern Europe. A year without summer for parts of the European continent if there is anything in this solar link I'm very dubious myself.
I believe it is more useful to remove the summers from 40+ years ago in a colder climate which is frankly gone, it yields a rather different result for UK and Ireland. This hints towards high-pressure ridging near Ireland (warm + dry?) interesting also summers of 1989, 2001 and 2014 were also thundery summers. Even not accounting for solar link other variables do appear to be quite supportive of an unstable summer.
Precipitation impacts from Hunga Tonga eruption
On 15 January 2022, the Hunga Tonga an underwater volcano launched 146 teragrams (Tg) of water vapour into the Earth's stratosphere equivalent to over 60,000 Olympic-sized swimming pools. Increasing the water vapour concentration by 10%. I do think this has played a part in the past 18 months being the wettest on record a new climate modelling paper reports the following: "Our WACCM simulations reveal significant surface temperature and precipitation anomalies globally which peak years 3-7 after the initial water vapour was injected into the stratopshere, e.g. years 2025-2029 got HTHH, but can appear earlier." Of course, there is significant uncertainty involved but this extended exceptional wet weather experienced since late 2022 not just isolated to UK but around world could be intensified, water vapour is a greenhouse gas as such Earth is likely warmer than it would be otherwise on the top of El Nino (2023-2024) there are reasons to believe this summer could bring exceptional downpours and rainfall to NW Europe and different parts of the globe. And to add on previous variables makes me believe a wetter summer is more likely than a dry one.
This plot shows a cross-section of the atmosphere at the equator we can see there is still significant and anomalous amounts of water vapour, especially in the lower atmosphere.
Seasonal models
Multi-model forecast for June-August 2024
The CS3 multi-system seasonal forecast is slightly supporting a wetter summer in Scotland and far north however, overall no real overriding signal for UK and much of Europe. Nonetheless, in terms of temperature, there is virtually unanimous agreement for a warm summer with the strongest and most frequent heat episodes in Southern-Southeastern Europe and weakest in Northern Europe.
My prediction
I'm expecting frequent and at times severe heat in southern and southeastern Europe, occasionally this is likely to move further northwards up into France and SE UK especially. These plumes from North Africa are likely to be intense and could bring very high temperatures but probably more short-lived heat in contrast to the Mediterranean region. I do not expect the summer to be great in northern Europe, I expect fine and warm weather to be punctuated by fresher and cooler oceanic air, which could give rise to thunderstorms.
June
It is very unlikely the summer will peak as early as it did last year, the first half of June is likely to be on the cooler side with winds frequently from the northern quadrant. This will be more unsettled for northern UK, I favour rainfall to be below average further south but temperatures are not likely to be spectacular. Late in the month, I see the potential for some hotter and drier weather from the south perhaps bringing the first 30C weather.
July
I foresee this will be the hottest summer of summer, indeed on average it is the hottest month of year, no shocker there with August in second, but I believe this summer month will stand out more than usual. Possibly the most prolonged settled spell of the summer. I also think this is when we are most likely to experience the hottest weather of the summer, extreme heat is favoured. A very warm summer is anticipated in the land areas of the Northern Hemisphere.
August
I think this will be a quite divided summer month the first half could see an extension of July's hot and settled spell, I do though think by this point northern Britain will see the seasonal deterioration has already kicked in well there's always September? Overall, the final month of summer has potential to be quite useable but it will be under threat.
Final comments
Overall, a warmer-than-average summer is likely in UK, however, northern Britain could see more average-below average temperatures and more frequent rainy spells. A hot and dry summer appears rather likely in S/SE Europe. In some way, this might be a more traditional summer with typical peak in midsummer, but the heat could be much more atypical. And downpours are likely to be heavier than usual a wetter summer is favoured over a drier summer, but regional disparities could be great. Thank you for reading.
If you want to see more posts like this in future and have a little to spare please support the website via Ko-fi link, costs are rising every year. I am also now also on Patreon linked below posting every Sunday where the survivability of these seasonal forecasts are guaranteed.
Comments