00:00Some parts of the UK are on day 11 of this third heat wave of the year.
00:05We had the early heat wave in May, followed by the humid heat wave in June,
00:10and now this particularly long-running heat wave in July.
00:15But what are the impacts of these three heat waves?
00:19In this week's Met Office Deep Dive, I'm going to be exploring the various consequences
00:24as a result of having so many bouts of hot weather so far this year.
00:29Impacts on our health, impacts on vegetation, and impacts on the seas surrounding the UK.
00:37And how long will this current heat wave last?
00:40Is there an end in sight? Is there any rain in the forecast?
00:44Welcome along to the Met Office Deep Dive.
00:46If you enjoy these in-depth explanations of the UK's weather,
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00:53because the more support we get, the more of these we can do.
00:57Now, I mentioned this is the third heat wave of the year so far,
01:01and this is beautifully illustrated by this graphic showing the maximum temperatures
01:06averaged across the UK from the 1st of April up until this point, mid-July.
01:12So, yeah, June, first half of July, we're now just about heading towards the halfway point of the summer.
01:20So, I thought it would be a great opportunity to do a half-time analysis.
01:25And what a summer stroke late spring it has been in the UK.
01:31The three heat waves really stand out on this as these three peaks.
01:36So, there's the late May one, above 25 degrees Celsius.
01:40Remember, these are maximum temperatures averaged across the whole of the UK,
01:43followed by the late June heat wave, again, a longer and higher spike there.
01:50And now this early to mid-July heat wave, once more, above 25 degree average,
01:58and lasting for considerably longer than the last two,
02:02although not with such elevated temperatures this time.
02:05And we're likely to see a gradual cooling trend during the rest of this week.
02:10More on that in a moment.
02:13But, yeah, quite an outstanding summer and spring so far.
02:17But not for everyone, of course.
02:18This map shows the maximum temperature for almost the first half of summer averaged across the UK.
02:25And we've got England and Wales, a considerable part of the southern half to two-thirds of the UK,
02:33above one and a half or two degrees Celsius.
02:35But Western Scotland, a little cooler than average, as far as maximum temperatures are concerned.
02:42I haven't got the rainfall map in front of me, but Western Scotland has also been the wettest place,
02:47with significantly drier than average areas across eastern England.
02:52This is the average rainfall compared with what we'd expect at this point for the summer so far.
02:59And, actually, you can see that this is what you'd normally expect, or this is the average, I should say,
03:04the black line running through the middle as the rain adds up through the summer.
03:10The average by the end of the summer is 250 millimetres across the whole of the UK,
03:16where the line here is above the black line.
03:19We've got this blue shading.
03:21That means that it's been wetter than average for a good part of June up to the first week or
03:28so of July.
03:28We were running up above average rainfall across the UK, obviously, with those regional differences.
03:34But now that running total of rainfall has dropped below the black line.
03:39So now below average rainfall up to this point, only slightly though.
03:44But again, very clear regional differences from the northwest of the UK to the southeast.
03:49But, yeah, it was a wet start to June for many parts of the country,
03:53which makes the current hot spell and the late June hot spell so remarkable
03:59that temperatures managed to get so high, despite it being, up to that point, a wet summer so far.
04:08This, though, is one of the standout statistics from the summer.
04:13What I've got here is instances of equal than or greater than 30 Celsius, 32 Celsius.
04:20Let's go back onto that and try not to touch it this time.
04:2430 Celsius, 32, 34, 35, 36, etc., all the way up to 40 Celsius.
04:30And which year had the most number of days equal to or greater than these temperatures?
04:37So starting at 30 Celsius, 1995 had the most number of days at or above 30 Celsius.
04:44You might remember it.
04:45It was the driest summer on record, even drier than the second driest summer on record, which was 1976.
04:51So no surprise that we saw the most number of days at or above 30 Celsius.
04:5634 days in total that summer.
04:592026 so far, up to the halfway point, of course, we're at 24 days.
05:03I say summer, but this is a count for the whole year.
05:07So, you know, some of these days occurred in spring, obviously.
05:1032 Celsius, again, 1995, the standout year.
05:1419 days that year at or above 32 Celsius.
05:18This year so far, 17 days.
05:22So another three days.
05:242026 will be the day with the most number of 32 Celsius days.
05:29Skipping those middle numbers for now, and you get up to the really extreme temperatures, of which we've only seen
05:36a handful.
05:3737, 38, 39, 40.
05:39And for 38, 39, well, for all of these numbers, really, 2022 was a standout year because, of course, they
05:45happen so infrequently.
05:462022, we saw two days at 37 and 38 and one day, of course, at 39, 40.
05:52So 2022, the remarkable year for those.
05:55But these middle numbers, these are the important numbers for this year because this year already we've seen the most
06:01number of days at or above 34 Celsius, 35 Celsius, and at 36 Celsius, tying with 2020, 2003, and 1990.
06:12So 9, 6, 3.
06:14And it's those mid-30s numbers that are important when it comes to impacts in the UK because impacts on
06:24infrastructure and people's health, well, they can vary considerably depending on a number of factors.
06:30But as a very rough rule of thumb, you typically be looking at the mid-30s temperatures for impacts to
06:41start to escalate in terms of roads melting, railways buckling, and widespread, not just localised, but widespread population impacts.
06:51So those mid-30s numbers are important, and this year has seen a remarkable number of those mid-30s.
06:59But temperature, of course, we kept emphasising this in late June, is only one aspect of things because I want
07:08to go back to that incredible heat wave at the end of June.
07:13It wasn't just about the air temperature, it was about the humidity, and this map here shows the wet bulb
07:24temperature from the 25th of June, the peak of the late June heat wave.
07:28This is the wet bulb temperature.
07:30We talked a bit about this at the time, but I'll just describe once again what the wet bulb temperature
07:35is.
07:36This wet bulb temperature is measured in a similar way to the air temperature, but with an extra component to
07:43the thermometer.
07:44The thermometer has a damp cloth attached, and that damp cloth then will evaporate water into the air surrounding the
07:54thermometer.
07:55And as that water evaporates, the air surrounding it cools.
07:59When water evaporates into the atmosphere, the air cools down, a bit like when we step out of the shower
08:05covered in water.
08:06That water is evaporating from our skin, we feel cooler, that's why we sweat.
08:10So, wet bulb temperature is a measure of how much the air is cooling as a result of evaporation.
08:19Now, the more water vapour that is already in the air, then the slower that evaporation will happen, and the
08:26less cooling you get.
08:28So, this is a really good indication of how humid it is, essentially, and, more importantly, the impact on our
08:37own bodies.
08:38Because, as opposed to thermometers, we cool down by sweating.
08:45And the higher the wet bulb temperature, the less efficient that sweating is.
08:51So, that's why the wet bulb temperature is so important, and it was crucial during that late June heatwave.
08:55We saw temperatures widely into the mid-30s, and in one or two spots, 36, 37 Celsius.
09:02But what was more important is that we saw wet bulb temperatures into the low to mid-20s.
09:08We saw observed values of 25, 26 Celsius, and that's what this map is showing.
09:15This is actually not the observed values, but the forecast values for the day.
09:18And I've coloured it up with five degree increments here, and given them little descriptions based roughly on some science
09:31about the upper limit and some dangerous temperature values.
09:34So, the upper limit for the wet bulb temperature for human survival, according to scientific research, is 35 Celsius.
09:41And that's because our skin temperature needs to be kept at around 34, 35 Celsius.
09:48And if you're not able to cool down below 35 Celsius by sweating, then your body can't cool down.
09:56So, this is the upper limit, and it's exceedingly rare to get wet bulb temperatures above 35 Celsius.
10:01So, that's the upper limit.
10:02Then, above 30 Celsius, still relatively dangerous levels of wet bulb temperature, and not that common across the world.
10:10But they have been observed in many places like India, Pakistan, the Persian Gulf states.
10:18They sometimes get into those values as well.
10:2125 degrees or above are put there as oppressive.
10:24And this map shows that we saw this swathe of mid-20s, 25, 26 Celsius, across central southern England into
10:35southeast Wales on that day, the peak of the heat wave.
10:38So, those particularly oppressive values, really quite uncommon for the UK.
10:44That's what we saw during that hot spell.
10:47Extending into the near continents as well, parts of France as well as the Netherlands and Belgium.
10:53But look how it compares with the rest of Europe.
10:56Not as high, even in some of the hotter countries across Spain and Italy and Greece, because humidity levels weren't
11:05as high, despite higher temperatures at the time.
11:07So, yeah, that value, the wet bulb temperature on that day, the peak of the heat, widely elsewhere, 20 to
11:1525 Celsius across Northern Ireland, Southern Scotland, England and Wales, a little bit more comfortable towards coastal parts and the
11:22far north and northeast.
11:23And that was a key reason why that heat wave was so dangerous.
11:30And you might have seen in the news a paper that came out, some research that came out this week
11:35that was researched, led by the Met Office, Imperial College in London, as well as, just get it right here.
11:50Met Office, Imperial College London, London School of Hygiene and Tropical Medicine.
11:55Now, they used historical mortality records and peer-reviewed methods to model fatalities during both the May heat wave and
12:05the June heat wave.
12:06And what they found was that 550 people are estimated to have died during the May heat wave due to
12:14heat-related causes, 2200 during the June heat wave, again, due to heat-related causes.
12:21So, these are estimates based on solid research and, of course, those two heat waves were boosted by climate change.
12:32It's reckoned that maximum temperatures were three to four degrees higher as a result of climate change than they would
12:38have been with the same weather patterns without global warming.
12:43And so, 42% of those heat-related deaths were reckoned to be attributable to the additional heat caused by
12:52human-caused climate change.
12:54So, really important research that came out and shows the impacts of these hot spells.
13:00Now, it's lovely in this country when we get some warm weather in the summer and we can go out
13:05and enjoy the sunshine and temperatures get into the high 20s, perhaps low 30s.
13:09Those are the kinds of temperatures, as you saw, we saw often in 1995, 1976 and so on.
13:17Thoroughly enjoyable warm weather, although still with impacts, of course, due to lack of rainfall and so on.
13:24But these heat waves, where we're getting more regularly temperatures into the mid-30s, can be much more impactful in
13:31terms of population health and other impacts.
13:34Now, one other impact, of course, is that despite the wet start to summer and a considerably wetter than average
13:44for many winter, we've seen a remarkable drying out of the ground during recent weeks.
13:49So, these two maps, these two satellite images, are separated by around seven weeks.
13:54This is late May and then you can see the colour difference by the start of July.
13:59It's not just about the lack of rainfall, which, of course, we haven't seen much of in July so far,
14:05but it's about the heat.
14:07The higher the temperatures are, the more evaporation you get.
14:10So, one of the things that can happen with these modern day heat waves is that you get the ground
14:16drying out much more quickly, despite seeing actually quite considerable rain in some places during the summer.
14:23As opposed to those much drier summers that we saw back in 1995 and 76, where you had barely any
14:31rain for weeks and weeks and months and months.
14:34These heat waves, you can get wet periods like we did at the start of June, but then very high
14:39temperatures, which rapidly dry out the ground.
14:41So, these remarkably different maps there emerging and what you could just about see there across Arbyshire and extending into
14:50northwest England and this plume of smoke is currently visible.
14:55Manchester Airport, this is the observation for Manchester Airport.
14:58This is the meter.
14:59This is what airports report.
15:01This is how they report the weather in the code here.
15:04And you might be able to make out, it's got 5,000, that's the visibility, 5,000 meters.
15:09And then this F-U, that's smoke.
15:12That's what the code is in a meter for smoke.
15:16Because meters, you might not know this, meters use a combination of English words and French words.
15:22So, sometimes the initials for weather are to do with the English word.
15:27So, for example, F-G would be fog.
15:29That's the English word.
15:30But F-U is fumé for smoke.
15:34So, that's the French word.
15:35But, yeah, not, doesn't happen that often.
15:38Manchester Airport reporting smoke and a reduction of visibility as a result.
15:42And this map here, it's only looking at England and Wales, by the way.
15:46It's not covering Scotland and Northern Ireland.
15:49But for England and Wales, it shows the fire severity index.
15:52And it shows it's either high or very high across England and Wales.
15:56What does this mean?
15:57It's not the risk of wildfires, but it is how severe a wildfire would be based on antecedent conditions if
16:06one were to develop.
16:08Now, although a lot of wildfires are started by people leaving barbecues around and sometimes by, sadly, arson as well.
16:18Well, this shows that the antecedent conditions can then really make it worse.
16:24It can fuel those fires once they start.
16:28And this takes into account rainfall, droughts of state of ground, temperatures, wind speed, really important, as well as wind,
16:40temperature, humidity, rainfall and drought.
16:44I was speaking to a Canadian meteorologist about a month ago for a separate video that we're working on.
16:51And in Canada, they use a 30-30-30 estimate as a rule of thumb for looking at wildfires.
16:58And 30 degrees Celsius, 30 kilometre per hour wind or above, and 30% relative humidity or below.
17:07Those are the three.
17:08If they happen together, then it's reckoned that wildfires are a greater concern.
17:15So, at the moment, we've got relatively high temperatures.
17:18We've got high 20s, low 30s across many parts of England and Wales.
17:22We've got very dry air.
17:24And, importantly, the last few days we've had this strong wind blowing across the south and the east in particular.
17:31So, the antecedent conditions are raised in terms of wildfire risk.
17:36It's not just the UK, of course.
17:38There has been some really tragic reports in the news in the last few nights about Spanish wildfires.
17:45And Spain has been particularly badly affected so far this year.
17:51It is the country in the European Union that has lost the most surface area due to forest fires during
17:58the first half of 2026.
18:00According to Copernicus, that's the European agency, fire has ravaged 50,000 hectares.
18:07And that's nearly 40% of the surface area burned in the EU so far has been in Spain.
18:12And we've seen those tragic reports in the news during recent days.
18:16This is a satellite image of the wildfire that's currently burning in France to the south of Paris, Fontainebleu Forest.
18:24You can see the smoke emanating from this area.
18:28There's active fire here and there's smoke going westwards.
18:32And this burn sky, there's a dark mark on the ground.
18:35So, a really significant fire there in France.
18:38Of course, France has had a truly exceptional summer so far.
18:42Regularly recording temperatures in the mid to high 30s and in some places the low 40s for days on end.
18:48It's very dry, very hot and right now it's windy as well.
18:53So, France, Spain, like the UK, wildfires are a real concern at the moment.
19:02One final serious impact of the heatwave, of course, is that we now have a marine heatwave across the UK.
19:09And in fact, on July the 10th, the heatwave category reached extreme with some of these areas around the south
19:18coast of England reaching threes and fours.
19:23And that indicates temperatures four to five degrees above average.
19:27So, surrounding UK waters on the 10th of July, we had well above average sea surface temperatures and extreme, well,
19:37strong to severe and in some places extreme marine heatwave conditions.
19:42That's come down a little bit.
19:44This is two days later, of course, we've had a bit more of a breeze to stir things up.
19:47So, it's mostly strong to severe.
19:49But the elevated sea surface temperatures are moving north, expected to cover much more widely the whole of the UK
19:56over the next week or so.
19:59With these marine heatwave categories varying in number from two to three in the south up to one to two
20:07further north across the UK.
20:09And you can see here how much the sea surface temperatures are raised surrounding the UK waters, above average virtually
20:16everywhere, but well above average around some of these western, southern and eastern coasts of England, as well as Wales.
20:22Not just the UK, of course.
20:25I talked about France having an exceptional summer.
20:27This is the Bay of Viscay, sea surface temperature this year so far.
20:32And 2026 is this line and it's already above the previous record for the Bay of Viscay, which was set
20:42in August 2003.
20:43That's this line here.
20:44So, it's already above that line.
20:46You'd expect temperatures in the seas in northern Europe to peak in August and September.
20:52And that's what happened in August 2003.
20:54This year, we're already above that previous record.
20:58So, truly extraordinary sea surface temperatures in the Bay of Viscay.
21:03We're talking about 24, 25 degrees or so.
21:06And this is the global perspective.
21:09Now, UK waters, Bay of Viscay, Mediterranean really stand out, these dark reds, four to five.
21:15And some parts of the Mediterranean, six or seven degrees above average right now.
21:20And a lot of red on this map.
21:22Not entirely red.
21:23There are some blue areas, of course.
21:25The most notable one being across the mid-Atlantic here, this blue blob that does make an appearance quite frequently.
21:33And that's an entirely separate conversation for another deep dive, I think.
21:37Another thing that stands out, of course, is this El Nino, very strong El Nino developing.
21:42And there's the signature across the Pacific of the El Nino, which is likely to, through this year, increasingly cause
21:51all sorts of disruptive weather patterns across the globe.
21:55Again, another topic for another deep dive.
21:59But one really important consequence of the marine heat wave, of course, for the UK is its effect on marine
22:10wildlife, algal blooms, as well as disruption to ecosystems and habitats and mass mortality of fish populations.
22:19And the introduction of new species, octopus, more jellyfish and so on.
22:23So really important for ecosystems surrounding the UK.
22:27You have to have temperatures around the coast that much above average.
22:30And it may well increasingly influence our own weather patterns.
22:36Now, those kinds of anomalies can reduce quite quickly if you get a windy spell.
22:40But if those anomalies remain, then you can see enhanced temperatures by night.
22:47That's one consequence.
22:48So higher nighttime temperatures because the land doesn't cool off so quickly.
22:52Another one is that if we get future heat waves, then those future heat waves are already boosted by the
22:57warm seas surrounding the UK.
22:59Another one, of course, is more evaporation.
23:01And as we get later into the summer, if we get unsettled weather, if we get rain, you get more
23:07rain as a consequence.
23:08So when it rains, it rains harder.
23:10And there's a greater risk of flooding then, not just through the rest of the summer, but into the autumn
23:15and winter if those anomalies remain.
23:18So, so many reasons why these sea surface temperatures around the UK and in the wider season oceans around the
23:26world are so important.
23:29Finally, how's it looking?
23:31For the rest of this week.
23:33How long will the heat wave last?
23:34I want to go back to this map, which showed the wet bulb temperature and how humid it was, how
23:39oppressive it was across much of the UK, away from central and northern Scotland on the peak of the June
23:45heat wave.
23:46Well, you've probably noticed it's not quite as oppressive right now.
23:50It's still humid.
23:51So still, we're seeing temperatures, wet bulb temperatures in the high teens, but it's not as humid.
23:58You can see that difference.
23:59Let's just switch it back.
24:01That's the late June heat wave.
24:04This is currently across the UK.
24:06And if I just skip forward over the next few days, what you'll notice is that something a little fresher
24:13is coming in increasingly from the east.
24:16So these more comfortable colours are coming in from the east.
24:20And temperatures on a whole are starting to reduce.
24:24So at the moment, we've got high pressure over the UK.
24:27We've got this fairly brisk easterly wind.
24:30Now, easterly wind is easing.
24:32But at the same time, high pressure by the end of the week is drifting to the northwest.
24:36And that's going to allow something a little fresher to recirculate around the high pressure.
24:41Still above average temperatures for many.
24:43But by the time we get to Sunday, those temperature anomalies are reducing.
24:47And so this is what the maps look like in terms of how far temperatures are above average.
24:55Widely well above average over the next few days.
24:57By the time we get to Friday, we've got these blues coming into the northeast of Scotland, eastern England and
25:01so on.
25:02If we move on a little bit, you can see something a lot fresher coming into the whole of the
25:07UK by Saturday and into Sunday.
25:10So things are gradually cooling off for the rest of the week.
25:13It's not going to be cold.
25:16Neither is it going to be unsettled.
25:18But the high pressure by the weekend is drifting into a position to allow something less hot to circulate around
25:25it.
25:25So we're talking by Saturday and Sunday temperatures in the mid to high 20s rather than the low 30s.
25:30The highest temperatures for Wales in the southwest and lower temperatures towards the east and the north.
25:38But through next week, that high pressure is staying close by.
25:41So if it is rain you're after, there is very little sign of it for the next 7 to 10
25:47days with high pressure continuing to dominate.
25:49One exception, of course, there are some thunderstorms expected to come up from the south and southwest over the next
25:55few days.
25:56That's covered in our daily national weather videos, which you can find on our YouTube channel.
26:01And the longer term outlook and whether or not we're going to see any substantial and usable rain in the
26:07near future.
26:08That will be covered in tomorrow's 10-day trend.
26:10But for now, that's all from me.
26:12I hope you enjoyed this week's deep dive.
26:14I know it's a little bit depressing at times, but hopefully useful information.
26:19And, you know, that's what these are there for, to give you this in-depth look at the UK's weather
26:26and, of course, its consequences.
26:29Thank you for joining me.
26:30That's all for now.
26:30Bye-bye.
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