- 4 weeks ago
This week's Deep Dive looks at one of the most remarkable climate stories of recent years: a potentially record-breaking El Niño and the weather events unfolding around the world as a result.
We explain what El Niño is, why the current event is starting to break records, and whether it has already surpassed the 2015/16 event. We also explore the difference between ONI and RONI and why meteorologists are pay attention to both measures of ENSO strength.
Bringing you this Deep Dive is Met Office meteorologist Aidan McGivern.
We explain what El Niño is, why the current event is starting to break records, and whether it has already surpassed the 2015/16 event. We also explore the difference between ONI and RONI and why meteorologists are pay attention to both measures of ENSO strength.
Bringing you this Deep Dive is Met Office meteorologist Aidan McGivern.
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NewsTranscript
00:00For some time we've been talking about this year's El Nino as the strongest in living memory
00:05and it's now starting to break records and cause impacts across the globe.
00:09But how will it develop in the next few months and will it affect the UK?
00:13Welcome to the Met Office Deep Dive. Thank you for joining me.
00:16We do these every Tuesday on our YouTube channel and in various other places that Met Office content can be
00:22found.
00:23If you like these in-depth discussions of the weather, please don't forget to follow us on YouTube,
00:27send us a like, send us a comment or a question and we'll try and answer your questions,
00:31of course, in our regular Weather Studio Live, which we do every Friday lunchtime.
00:36Now, we've covered El Nino and its impacts across the globe in previous videos,
00:42but it is an evolving situation. It is the biggest weather impact and climate impact to be talking about this
00:49year.
00:49So, of course, we're going to be covering it again and again.
00:52And I wanted to cover it in this week's Deep Dive because it's now getting to the point that it's
00:57breaking certain records
00:59and causing really significant global impacts.
01:01I will later on talk about the UK's weather over the next few days and what we can expect into
01:06next week.
01:07But first of all, let's take a look at the state of El Nino at the moment and how it
01:12is affecting global weather.
01:14Now, how do we define El Nino? We've covered this before, but very quickly, El Nino essentially is a change
01:22in the trade winds
01:23across the Pacific and a warming of the seas in certain parts of the Pacific as a result of those
01:30changes in the trade winds.
01:32Typically, trade winds run from east to west across the Pacific, push a load of warm seas towards Indonesia
01:40and northern Australia, causing a lot of heat here and intense thunderstorms to develop,
01:45but at the same time causing upwelling and cooler seas around the coast of South America, drier air here as
01:54a result.
01:54That's your typical state of affairs.
01:57But there's an oscillation called the El Nino Southern Oscillation,
02:01in which sometimes, every two to five years, those trade winds across the Pacific weaken.
02:09And as a result, less warm water is pushed westwards and that warm water ends up being focused more towards
02:15central and eastern Pacific.
02:17There's less upwelling off the coast of South America.
02:19The seas warm in this region and the thunderstorms that you typically get around Indonesia, northern Australia,
02:25become redistributed more towards the central part of the Pacific.
02:28So, of course, that, being El Nino, causes significant ramifications for countries and continents bordering the Pacific,
02:38but also elsewhere in the world because of vast changes in ocean and atmospheric conditions and atmospheric circulation
02:48as a result of the redistribution of the ocean heat and redistribution of those very intense thunderstorms.
02:55In a La Nina year, the opposite happens.
02:59You get a strengthening of the trade winds.
03:00You get more warm water pushed towards western parts of the Pacific, Indonesia and so on.
03:05So, it's more of an exaggeration of what you typically find, more rain over Indonesia,
03:09drier over coastal parts of South America, eastern, western parts of South America there.
03:15What we are currently seeing is El Nino.
03:18So, that's a warming of this region and a redistribution of these thunderstorms drying up over Southeast Asia,
03:26wetting up across coastal parts of western South America.
03:30And you can see how much warmer those seas are compared with average.
03:35This compares it with the 30-year average from 1991 to 2020.
03:38This is from Sunday the 20th of September.
03:41So, you can see this huge area of warmer seas.
03:44And the box area, that's called the Nino 3.4 area.
03:49And that's the key bit where scientists monitor the progress of El Nino.
03:55It's the temperatures in that box, the sea surface temperature anomalies,
04:00that determine whether or not La Nina or El Nino is happening.
04:05If the temperatures, the sea surface temperature anomalies in that area are 0.5 degrees above average
04:11for a three-month average over five overlapping seasons,
04:19then an El Nino is declared.
04:20That happened earlier in the summer.
04:21But since then, those sea surface temperature anomalies have been rising and rising and rising.
04:27And although, officially, how we define El Ninos and how we measure certain El Ninos with other El Ninos
04:36is defined by a three-month average with this box.
04:39That's the index called the Oceanic Nino Index.
04:44So, this is the three-month average.
04:46That's how we compare various El Ninos.
04:50The strongest El Nino record was 2015 to 2016.
04:54That had a three-month average of 2.6 Celsius above average for those sea surface temperatures.
05:01There's also a daily anomaly.
05:03And that's what I want to look at right now.
05:06And this graph shows the daily anomaly.
05:09Appreciate.
05:10It might be difficult to make out all the faint lines on here.
05:14It's all white.
05:14It's not our graph.
05:16It's from climatereannialiser.org.
05:19So, you can look at it in detail if you go to this website here.
05:24And you'll easily be able to find this daily sea surface temperature graph for the Nino 3.4 region.
05:32And the key takeaway from this is the 2026 line, which has been rising all summer in terms of the
05:40sea surface temperature anomaly.
05:41And that's the anomaly compared with a 30-year average.
05:45And it's now at 3.05 Celsius above average for that box area.
05:52That's the latest daily anomaly, not the three-month anomaly.
05:56The latest daily anomaly, which, of course, can go higher than the three-month average.
06:02But that now places it higher than this point here, which, again, I appreciate it's difficult to see it.
06:10Apologies for that.
06:11But this is the point, the peak of the 2015 El Nino, which peaked in the middle of November at
06:193.02 Celsius as an anomaly.
06:23So, it's now, towards the end of September, higher than the peak of the 2015 El Nino.
06:32And that peak was in November, which is around the time this El Nino is expected to peak.
06:37So, we're two, perhaps three months away from the peak of this El Nino.
06:42The daily sea surface temperature anomaly is higher than the peak of the strongest El Nino on record.
06:50So, that's how remarkable this El Nino has become.
06:54It's already surpassing the daily peak, not the three-month average peak just yet.
07:00I'm sure it will later in the summer, later in the year, because the Met Office projection is for the
07:07three-month average to be around three to three and a half degrees above average for the sea surface temperature
07:15anomaly.
07:16And other centres around the world have similar, if not warmer, predictions for the peak of El Nino.
07:22So, this is, as expected, turning into a truly exceptional El Nino.
07:27One more graph to show you on this is a similar kind of graph.
07:32Again, it's not a Met Office-produced graph.
07:35This is from climatebrink.com.
07:37So, apologies if it's not entirely clear on your screens.
07:41But this is showing the same thing, the ONI, the Oceanic Nino Index, for each day of the year so
07:48far.
07:48And the red line here shows our current year, 2026, plus 3.1 degrees Celsius.
07:54So, it's rounded up there because I mentioned 3.05 for the previous graph.
07:58So, it's rounded up to 3.1 there.
08:00And it's at around the peak of the, or similar to the peak of the 2015 El Nino.
08:07But what's interesting is if I click onto the next graph, which shows a slightly different index called the Relative
08:14Oceanic Nino Index.
08:16And basically, the difference is that this, for each year, compares it with the 30-year average.
08:24But the next graph, the Relative Oceanic Index, is comparing the temperature anomaly in that Nino 3.4 region with
08:35the tropical oceans around the world.
08:37And what's significant about that is that it's then taking into account the general warming of the oceans and the
08:45tropics around the world.
08:46In other words, if the oceans, the tropical oceans, have warmed by half a degree in the past 30 years,
08:54then that's taken into account.
08:57Because what's important when you consider El Nino is the relative warmth of that Nino 3.4 region compared with
09:07the tropical oceans.
09:08Not necessarily how it relates to the 30-year average, although the 30-year average index is important for comparing
09:17various El Ninos.
09:19But the impacts from El Nino are more related to how much warmer that box area is compared with tropical
09:27oceans as a whole.
09:28So if all the tropical oceans are warmer as a result of global warming, then it's perhaps not quite as
09:36significant, the warmth of this current El Nino, as this graph might suggest.
09:43So I'm just going to click onto the relative ONI, and you can see it's not quite there in terms
09:51of the peak compared with 2015.
09:53It's still got half a degree or more to go.
09:57It's a bit closer to 1997-2015 previous years.
10:03It's still above them. It's still an exceptional event.
10:05It's still likely to exceed all previous years, but by a slightly lower, say half a degree gap when you
10:18compare with previous years, taking into account the fact that the oceans have warmed anyway.
10:23So there are different metrics essentially for measuring El Nino and for comparing different years with each other.
10:31However, what is important to say is that, yeah, this one is going to be the strongest in living memory.
10:39It's going to cause really significant impacts.
10:42However, when you take into account the fact that tropical oceans around the world have warmed even since 2015,
10:50then that difference becomes slightly less compared with other years.
10:56Nevertheless, it is already causing really substantial impacts.
11:01Just to take a look around the world.
11:06And remember that sea surface temperatures are exceptionally warm around the coast of western parts of South America at the
11:15moment.
11:15This shows the total rainfall expected over the next few days.
11:20And there are a couple of regions to pick out.
11:22I'm going to go to Saturday.
11:23So this is the total amount of rainfall expected from now until the end of Saturday.
11:28One part of the world to point out.
11:31Parts of Chile down here where 100 to 150 millimetres, perhaps as much as 500 millimetres accumulating over the mountains.
11:42A lot of rain expected between now and Friday in this region.
11:47It's already been very wet recently.
11:49So this increases the risk of flooding, increases the risk of landslides.
11:54Significant mountain snow as well above two and a half thousand metres.
11:57So, yeah, a lot of rain here.
12:00And that's because of a very active jet stream.
12:02Just going to click onto the jet stream there.
12:04Next few days, you can see that jet stream bringing a succession of low pressure systems in.
12:09They're calling it an atmospheric river event.
12:11I know they talk a lot about atmospheric rivers when it relates to rainfall in California.
12:16But you can see that jet stream driving these areas of low pressure and rain, by the way, and rain
12:21into this part of Chile.
12:24Now, over the weekend, the jet stream will start to ease.
12:28You can see it's moving away, but still some rain remaining.
12:32So that's one part of the world where there'll be some significant rainfall over the next few days.
12:38Because of an active jet stream and higher sea surface temperatures.
12:42Another area, Ecuador and Colombia.
12:46So in this region, yeah, 150, 200 millimetres widely.
12:50As much as 500 millimetres over the western part of the Andes.
12:56And that would be equivalent to about a month's worth of rain in just a few days.
13:02So another wet part of the world here.
13:04Again, because of high sea surface temperatures, a lot of heavy rain and thunderstorms expected over the next few days.
13:12But move further north, some very wet weather across Mexico.
13:15And it's here, although it doesn't show up too much.
13:19But it's here where there's likely to be impacts from a very quickly developing and intensifying hurricane called Hurricane Polo.
13:30Now, just a quick word on Hurricane Polo.
13:33It is called Hurricane Polo because not all tropical cyclones in the Pacific are called typhoons.
13:42Last time I did an El Nino update, I talked about hurricanes in the Pacific.
13:46And a number of people said, aren't they called typhoons?
13:50Not if they're east of the dateline.
13:52I mean, when they're east of the dateline, the National Hurricane Centre looks after them or monitors them.
13:59They don't look after them, but they monitor them closely and they name them.
14:03So they're called hurricanes if they're east of the dateline, west of the dateline.
14:07They're called different things depending on whether they affect Australia or India or Japan and so on.
14:13But this is Hurricane Polo.
14:15And it's intensified in the last 24 hours up to the time of recording.
14:2090 knots has been the increase in wind speed close to its centre.
14:26It's a very compact hurricane.
14:28So hurricane force winds only extend out to 30 miles away from the ice.
14:33That's really not a big region.
14:35And it is expected, hopefully, to veer away from Mexico.
14:40So the main impacts likely to be life-threatening surf, sea surge and some very heavy rainfall over the next
14:47few days.
14:48But it's expected to strengthen into, well, it is already a major hurricane.
14:53It's expected to strengthen into Category 5 by the end of Tuesday.
14:58But you can see how it moves away from Mexico because of this ridge of high pressure that's building across
15:03Mexico.
15:05This isn't the only developing system in the Pacific.
15:09The Pacific is very active at the moment.
15:12I was talking to our expert on this, Julian Hemming, earlier.
15:16And he said that if all the developing areas across the Pacific east of the Dateline become tropical cyclones in
15:27the next few days,
15:28then there'll be four concurrent tropical cyclones east of the Dateline.
15:32The record is five back in 1974.
15:35But I've talked before about the activity in the Pacific.
15:40Maybe you get a sense of it from the fact that we're on P for polo.
15:45But it's been a very, very active season so far.
15:48You can pick out a few here.
15:51Or Dallas there.
15:52Tropical storm.
15:53And polo there.
15:56Another depression that may develop into something that could bring some very heavy rain across Hawaii over the next few
16:05days.
16:05So all these systems are developing because during an El Nino year, particularly in an extraordinary El Nino year like
16:13this,
16:13we've got the high sea surface temperatures providing the energy.
16:16We've also got lower wind shear that helps to keep these systems organizing rather than blowing them apart.
16:23A contrast to the Atlantic.
16:25More on the Atlantic in a moment.
16:26But while we're talking about these developments, there are other developments on the other side of the Pacific.
16:34Something that's likely to develop into a typhoon.
16:37Moving away from Japan.
16:39Lots of things going on.
16:41But here's an exception to the rule.
16:44Now we've talked about the above average activity in the Pacific because of El Nino.
16:50What you'd normally expect around the Bay of Bengal, India, is suppressed activity from cyclones and from heavy rain and
17:01so on.
17:01And that has been the case so far this year.
17:05The Indian monsoon starts in June and up to this point there's been a deficit on average across India of
17:1115%.
17:1215% less rainfall than normal.
17:15And in some regions of India, 40%.
17:19Now 15% might not sound like much.
17:2140% certainly a lot higher.
17:23But that's already a significant deficit in terms of causing serious problems to do with agriculture.
17:31And of course that can impact food production and, you know, ramifications as a result on the global food supply
17:40chain.
17:40So, this is an exception to the rule.
17:45We've talked about it being dry and you'd normally expect that with El Nino.
17:49But here's a depression that's actually developing in the Bay of Bengal and is expected to intensify.
17:55It's not going to spend too long over open waters.
17:57So, that will limit some of its development.
18:01But it may well develop into a tropical cyclone.
18:04And here it is pushing into India and bringing some very heavy rainfall as it crosses from the southeast and
18:12pushes northwestwards over the next few days into the weekend.
18:15How much rainfall are we expecting?
18:17Let's go back onto that rainfall graphic.
18:21In fact, if I play this, I'll zoom in a bit.
18:24You can see how the rolling rainfall totals build up over the next few days.
18:29So, already Wednesday, very wet around the coast there of eastern parts of India.
18:36And then as we skip forward, some of these reds are starting to appear.
18:40200, 250 millimetres.
18:43Quite widely, 250 millimetres or more.
18:46Widely, 300 millimetres developing over the next few days.
18:49And then those very heavy rains push northwards.
18:53So, yeah, like I say, that's an exception.
18:56Another exception to the rule, as far as El Nino is concerned, is this enhanced rainfall across parts of Thailand
19:03and Cambodia over the next few days.
19:05So, some wet weather around in those areas where you typically get less rain.
19:10But on average, so far, India has followed the theme of drier-than-average conditions.
19:17As has Indonesia, where I read one region in Indonesia has now gone 131 days without rain.
19:27131 consecutive days without rain.
19:30It doesn't happen often in Indonesia.
19:32It is a wet part of the world.
19:34Lots of thunderstorms normally take place.
19:36So, all sorts of things happening around the globe at the moment.
19:41One thing that's not happening, Atlantic hurricanes.
19:44We haven't seen a single one and we've now gone past the peak as far as Atlantic hurricanes are concerned.
19:52The peak, of course, earlier in September doesn't mean there won't be any.
19:57But there are no signs in the next week or so of anything intensifying across this part of the Atlantic.
20:05There is a tropical storm, Faye, that developed just to the south of the Azores.
20:12Here it is.
20:13It's now going to peter out.
20:15It's not going to develop into a hurricane.
20:17We've seen a few tropical depressions, tropical storms.
20:19But what happens in an El Nino year, and that's certainly been the case this year, is you get enhanced
20:25wind shear.
20:26That means that's the difference between the wind speed and or direction at the surface and higher up.
20:32And, of course, if you've got more of a difference in wind speed and or direction, then these hurricanes can
20:38be torn apart before they get a chance to develop.
20:41So, that's certainly the theme with El Nino.
20:44And this year, we've gone past September the 11th, which in the satellite era was the date for the latest
20:52named hurricane.
20:54So, we've gone past that.
20:55When you look further back, we've now gone past the date, which was, I believe, September the 21st or September
21:02the 22nd for the latest hurricane in the non-satellite era.
21:07Although there were two years, 1907 and 1914, in which no hurricanes in the Atlantic were named.
21:16But, of course, that's going so far back that data was sparse.
21:20So, we don't really know for sure whether or not that happened.
21:24There are some reanalyses that suggest that there would have been hurricanes then.
21:30But, you know, we didn't have satellites, we didn't have the monitoring that we've got in the modern day.
21:34So, in terms of the reliable record, it is now the latest and, you know, keeps on getting later for
21:41the first named hurricane in the Atlantic.
21:43There is some signs of an African easterly wave coming off Africa and could develop into something.
21:51But no models at the moment strengthen that into anything significant.
21:56One thing, again pointed out to me by Julian, that is interesting to monitor later this week and into the
22:04weekend,
22:04is a developing low off the coast of North America, about 35, 40 degrees north.
22:14So, quite far north. Here it is.
22:16And this system could become really quite deep, as you can see, and bring some impacts to New York, New
22:25England,
22:26in terms of rain and wind, some very stormy weather.
22:30But there's an outside chance that this system, at the same time as becoming strong enough to be hurricane force,
22:38off the coast of North America, could just about develop some tropical characteristics
22:43and become what they call an instant hurricane.
22:46So, it's, you know, strong enough to be a hurricane, but not a tropical storm.
22:51And then it develops some tropical characteristics, like a warm core as opposed to a cold core, that sort of
22:57thing.
22:58And then suddenly it's a hurricane.
22:59So, if that happens, then, you know, the first named hurricane could, and it's an outside chance,
23:06but could be this system, which is well away from the tropical Atlantic.
23:10One to watch, if nothing else, because of the impacts from rain and wind that are likely to happen to
23:17North America.
23:19And, just ahead of my discussion about the UK's weather, as that system develops,
23:25let's take off the rain and put on the temperatures.
23:27As that system develops, all this warmth that it generates, and there's a little bit of a branch of a
23:34jet stream down here,
23:36but at the same time, there's a much stronger jet stream further north.
23:39Now, if that warmth gets pushed north, all of that energy associated with that developing area of low pressure
23:46colliding with the jet stream, and colder air coming down from Greenland,
23:52that may serve to strengthen the jet stream over the Atlantic,
23:57which then subsequently going to next week could have impacts on the UK's weather.
24:02And I'll cover that at the end.
24:04But, for now, that is definitely an area of low pressure to watch for several reasons.
24:10One final thought on El Nino is this rainfall forecast, this precipitation forecast for the next three months.
24:22And it shows a lot of the kinds of things you'd expect with an El Nino.
24:28But every El Nino is different.
24:32So, they don't all follow the same rules for different parts of the world that you might expect from previous
24:40El Nino's.
24:41And this is the precipitation forecast, issued September 2026, for October, November, December.
24:46Just to point out a few regions, I mentioned Ecuador there, above average rainfall, Chile as well.
24:53Here's another place where above average rainfall is likely, Uruguay, Paraguay.
24:56But these reds here, these intense reds across parts of Central America into Brazil,
25:02so a drying up of the Amazon, that's what you'd expect with El Nino,
25:06and that is currently projected for the next three months.
25:09Also, some wet weather pushing into California, New Mexico, other parts of Mexico as well.
25:15Meanwhile, on the other side of the Pacific, a very notable dry signal there for Indonesia.
25:22Again, what you'd expect.
25:23Very wet there off the Horn of Africa.
25:26Another thing you'd expect, drier for India.
25:29Parts of Southern Africa, drier.
25:31That's another telly connection to do with El Nino.
25:35And closer to home, this blue area just to the southwest of the UK.
25:41Compared with these other wetter than average areas, it's not quite as strong.
25:44And of course, with the UK, El Nino is only one of several impacts that can determine the UK's weather.
25:53Because we're not bordering the Pacific, we're bordering the Atlantic.
25:56So we don't have such a strong association with El Nino as coastal parts of Western South America,
26:05Western US, Indonesia.
26:06There's not that really strong correlation, but we do have impacts.
26:11And one of the impacts is that because of this redistribution of sea surface temperature, warmth and thunderstorms over the
26:18Pacific,
26:19you tend to get an energetic jet stream running across the Pacific into North America,
26:25and then subsequently having downstream impacts on the UK, which can lead to lower than average pressure to the west
26:31of the UK or the southwest of the UK,
26:33and above average rain, increased chance of storminess during this period, October, November, December.
26:42Now, this isn't, and don't let anyone tell you, this is definitely going to happen because of El Nino.
26:49Like I say, it's one influence on the UK's weather when you've got a whole globe's worth of influences competing
26:59with El Nino on the UK's weather.
27:02Another thing that we are seeing that increasingly influences the UK's weather, of course, is the average warming of the
27:08planet that causes a greater chance of wetter winters.
27:14So, that El Nino influence loads the dice for the UK towards wetter than average weather, October, November, December.
27:24So does climate change.
27:25But then there are other, obviously, other influences.
27:29There's random variability, season to season, every season different and so on.
27:33The position of the jet stream varies each season.
27:36The strength of the jet stream, the storm track of the lows.
27:39All those things vary.
27:42All I'm saying is that El Nino loads the dice in favour of wetter than average spell, October, November, December.
27:51It does not guarantee it.
27:52Likewise, when I've done videos on El Nino in the past, I've seen in the comments that people have said,
28:00oh, El Nino means we'll get snow at the end of winter.
28:03It doesn't mean that El Nino increases the chances of sudden stratospheric warming events later in the winter.
28:13It, again, loads the dice in favour of sudden stratospheric warming events later in the winter,
28:19which subsequently can increase the chances of colder weather for the UK.
28:25But it doesn't guarantee them by any stretch of the imagination.
28:30You know, when you look back at 2015, 2016, the strongest El Nino on record, we didn't have a particularly
28:37cold end to winter.
28:38It was kind of wet and mild throughout December, January, February.
28:43So increasing the chances of something doesn't necessarily guarantee it.
28:47Our weather in the UK is affected by many things.
28:52And if you're confused by what I meant by sudden stratospheric warming, we've done a really good explainer video on
28:58that.
28:59It's essentially the disruption of a circulation of winds in the polar stratosphere.
29:04And when we get that disruption, then it can have downstream impacts on the strength of our own jet stream
29:10and increase the chances of easterlies or northerlies in the UK.
29:14But again, increasing the chances doesn't mean these things are guaranteed.
29:19So, yeah, anyone who says El Nino will cause this or will cause that or definitely means this or that
29:26for the UK, don't listen to them.
29:29And it increases the chances of these things rather than guarantees them.
29:35But for the UK itself at the moment, never mind cold, it's been really quite warm.
29:40At the time of recording, the highest temperature so far today has been 26 Celsius, but it's expected to go
29:46a little bit higher into the afternoon.
29:48These are temperatures that would be slightly above average for July, never mind the end of September.
29:54And the fact that we've got the autumn equinox tonight, five past midnight GMT, the northern hemisphere starts to tilt
30:01increasingly away from the sun.
30:03It's not that common to get those kinds of temperatures at this time of year.
30:09And we've got a lot of warm weather across the south and southeast of the UK.
30:13But at the same time, we've got increasingly wet weather into the northwest of the UK.
30:17And I just wanted to touch on that for now because it's quite interesting, this weather front.
30:23It's initially a weaker fare because it's running into high pressure.
30:29But overnight, gone a bit far, overnight, that's going to intensify.
30:35It's going to bring some heavy and prolonged rain to central and western Scotland, northern Ireland, a few showers ahead
30:41of it.
30:41Here we are during the early hours. Expect some noisy rain on your bedroom window overnight across central parts of
30:51Scotland into the south of Scotland.
30:52Some showers into northern England. Rain clearing northern Ireland at this point.
30:57But by the start of Wednesday, a tricky rush hour, I think, for eastern and southern Scotland, northern England, as
31:04well as north Wales.
31:05Some heavy rain and some showers just ahead of it there into central parts.
31:09And what's happening is that although that front is pushing into an area of high pressure at the surface,
31:16we need to look higher up at the jet stream for what's going on that will allow the rain to
31:23turn heavier for a time.
31:25And it's this sharpening upper trough, this area of low pressure higher up in the atmosphere that causes rising air
31:33despite high pressure at the surface.
31:35And it's that sharpening upper trough that comes along overnight and interacts with the rain to cause heavier rain to
31:44develop.
31:44And we're talking about, you know, during Wednesday morning, 25 millimetres fairly widely, the south and east of Scotland, 35
31:52millimetres in a few hours in places.
31:55And as I keep playing through the morning here, what you can see by the middle of the morning, some
32:02quite angry colours there as the rain pushes into parts of Wales and northern England.
32:06But at the same time, there's likely to be some really quite lively showers.
32:11Just pick the right moment because it all happens quite quickly.
32:14Late morning, really quite lively showers ahead of that.
32:17Here's the jet stream diving to the south.
32:20We're in this peak upper trough zone across parts of northern and eastern England.
32:27And these heavy showers that happen just ahead of the cold front.
32:31There's the cold front associated with the rain.
32:34Well, they are likely to be associated with frequent lightning, two centimetre hail, 20 millimetres of rain in an hour
32:41or so.
32:42So, not going to happen everywhere.
32:44So, hit and miss, but across parts of Lincolnshire, perhaps Norfolk into parts of Yorkshire, the North Midlands.
32:53You can see how that does move through quickly, but could bring some impacts because the intensity of that rain
33:00as it moves through.
33:02By the middle of the afternoon, most of the UK turning drier once again.
33:06A little bit fresher, not as warm as today.
33:09Still, most of the south of England, South Wales, largely missing the rain.
33:15And with some sunny spells, low towards mid-20s, 23 Celsius also.
33:22But the cold front is bringing fresher air in and high pressure builds in behind that.
33:27Just a few showers for the north of Scotland.
33:28And with that high pressure in place, as we, you know, appropriately enough, go through the autumn equinox,
33:37it's going to be a chilly night fairly widely across the UK.
33:40We're talking about high to mid-single figures widely, perhaps low single figures,
33:45or even a touch of air frost for sheltered parts of Scotland, low single figures for sheltered parts of northern
33:50and central England, as well as Wales.
33:52So, yeah, a much colder start to the day tomorrow compared with what we've been used to recently.
34:01But lots of sunshine around first thing.
34:03And as a result, temperatures rising fairly widely into the afternoon.
34:07Only ahead of the next system, though, which by the afternoon is already bringing increasingly strong winds into the west
34:13of Scotland,
34:13Northern Ireland and some heavy rain.
34:16And this is the way it continues over the next few days.
34:19We're going to see it turn warmer once again in the southeast of England.
34:22If I skip forward to Friday, Friday is another day where we're likely to see temperatures reaching the mid-20s
34:28in the southeast.
34:28But at the same time, we're going to see more changeable weather increasing the effect of the north and west.
34:32Fronts moving in, followed by showers.
34:35Likewise into Saturday, mostly dry in the southeast.
34:39Fronts, gusty winds, showers coming into the northwest.
34:42Sunday, again, we've got these fronts moving in.
34:45Heavy rain at times, followed by showers, but mostly dry and sunny towards the southeast.
34:50And where we get that warm sunshine, even if it is getting increasingly weak at this time of year,
34:56still the potential for low to mid-20s at times in the southeast.
35:00So, more of the same, essentially.
35:03Very changeable in the northwest.
35:05Autumnal, fresh, gusty winds here with showery rain at times.
35:09But warm, early autumn weather in the southeast.
35:16Now, I did mention earlier that that low pressure off the coast of North America could influence the UK's weather
35:23by firing at the jet stream early next week.
35:26And there's some uncertainty at the moment, as is actually the case when looking that far ahead,
35:32in terms of where any low pressure will end up.
35:36Actually, a good way of looking at that is to look at every single run of the European model.
35:43It's run 51 times.
35:44And these are all represented here.
35:46This is Tuesday, the 22nd of September, 1 o'clock.
35:49Time of recording.
35:50But if we go forward to the following Tuesday, I'll go back a little bit there.
36:00This is 4 o'clock next Tuesday.
36:02So, we're looking ahead a week.
36:04So, naturally, there are differences when you look at all these different computer model runs.
36:09Why did we run it 51 times?
36:10Because of chaos theory.
36:12The idea that as you go increasingly further ahead into the future,
36:16subtle changes at the start of the forecast can escalate quite significantly into the future.
36:19And if, looking seven days ahead, most of the models are saying a similar thing,
36:26we can be confident that that's likely to happen because those subtle changes at the start
36:30aren't causing big differences into the future.
36:33And looking at all 51 of these runs for next Tuesday, there are commonalities.
36:40Most of them have some form of low pressure close to the UK.
36:44And where there is a low pressure close to the UK, most of them have it just the west of
36:49the UK.
36:49There are some really quite deep lows coming through.
36:53For example, this member here and this one here, here would bring very strong winds to Northern Ireland, Western Scotland.
37:03Some of them have the low over Scotland, for example, here and here.
37:09But most of them have some form of low pressure over or more likely just to the west of the
37:17UK.
37:17But there are some really quite deep areas of low pressure.
37:20I'm just going back onto this and selecting the control run.
37:24And again, going to Tuesday.
37:29Here's what the control run of the European model would suggest.
37:32The control run, by the way, is where it's fed the best possible information at the start.
37:37But all the other runs have that information slightly tweaked.
37:40And they may act as a guide in terms of how those subtle differences change into the future.
37:47But look how deep that is.
37:48Loads of isobars surrounding it.
37:51Thankfully, keeping the strongest of the winds, which would be around here, just to the west.
37:56But yeah, it would bring some wet and windy weather for sure, Tuesday.
38:00And as I mentioned, that's a result of the jet stream being fired up over the Atlantic and developing an
38:07area of low pressure like this really quite quickly.
38:10But what we can do here at the same time is to put on all the tracks from all of
38:15those different computer simulations.
38:17And you can see they're all over the place, but they're mostly to the west of the UK.
38:22So quite a cluster of them to the west of the UK.
38:25Not many over the UK at this point.
38:26That does increase slightly if I move it forward.
38:30But yeah, most of these tracks take it between Scotland and Northern Ireland.
38:36So just flagging it for now, it is seven days ahead.
38:39Naturally, there's some uncertainty in terms of the track, the depth and the location of that area of low pressure.
38:44But there is the potential for a wet and windy spell as a result.
38:48And the greatest risk of strong winds and impacts from the winds and the rain would be towards the northwest
38:54of the UK rather than towards the southeast.
38:57So certainly one to monitor.
39:00And an active jet stream and deep areas of low pressure to the west of the UK, of course, one
39:04of those things that can be linked to El Nino.
39:08But it would be too early and too small a sample size to directly link this area of low pressure,
39:16of course, to the developing El Nino because we get lows like this all the time in autumn.
39:21So yeah, just to flag it for now.
39:23And we'll be keeping an eye on it very closely.
39:25But for now, that's all from me here in the Met Office this week's Deep Dive.
39:31Hope you enjoyed it.
39:32Do let me know if any of it didn't make sense.
39:35I'll try and explain or answer any questions in the comments, should you have any.
39:42But for now, that's all for me.
39:44Bye bye.