Deep Dive 06/08/2024 – Hurricane Debby could influence the UK – Met Office weekly weather forecast UK
This is an in-depth Met Office UK Weather forecast for the next week and beyond. Could the remnants of hurricane Debby mix the weather up across the Atlantic and generate some hot ait for parts of the UK next week. Bringing you this deep dive is Met Office meteorologist Alex Deakin.
Category
🗞
NewsTranscript
00:00Have we got a deep dive for you today?
00:03And I say we, I'm not just talking about me
00:05and Rich who's recording it next door.
00:07There's gonna be four of us talking you through the weather
00:10and some other interesting features of meteorology
00:13over the next half an hour or so.
00:16Welcome along, my name's Alex Deakin,
00:18I'm a weather presenter here at Met Office HQ.
00:21This is the deep dive, we do it every Tuesday
00:24and we really appreciate and love your feedback
00:26and your comments, so do please keep them coming in.
00:29Hit that like button as well
00:31and if you're not already subscribed,
00:33make sure you do because this is the only place
00:35that you can catch our deep dive every Tuesday,
00:38so do hit subscribe to our channel as well.
00:41That would be fantastic, as I said, plenty to get through.
00:45Coming up later, we have a very special interview
00:48with a ballooning expert.
00:51I'm also gonna be joined by a deputy chief meteorologist
00:54because the heat is likely to return.
00:58I know some parts of the UK haven't seen much heat at all
01:01so far through this summer, but some areas have
01:04and it's gonna be similar areas
01:06that potentially have some heat coming back
01:07for the early part of next week,
01:09so we'll be going in depth talking about that
01:13and we'll also be looking at Storm Debbie.
01:16What was Hurricane Debbie is bringing devastating floods
01:20to parts of the United States
01:22and what happens to Debbie next?
01:24Could it influence our weather in some way?
01:28We'll be going into the detail of that as well.
01:31So as I said, plenty to talk about.
01:33Let's start off with the satellite image.
01:35Here's what's going on at the moment.
01:37You can see the swirl, that's an area of low pressure
01:40and this is a line of cloud, a trailing weather front
01:43that's just trickling its way across East Anglia
01:45and the Southeast of England at the time of recording.
01:48You can see that swirl up there,
01:50that's the low pressure system
01:52which is bringing us the wet weather.
01:54The jet stream is on here.
01:56These are the winds high up in the sky
01:58where the aeroplanes fly,
02:00but the jet's in a bit of a mishmash at the moment.
02:02There's no strong pink colors, the core of the jet.
02:06So the jet's not particularly strong.
02:08It's in a bit of a mishmash,
02:09but it's just helping to keep this low pressure
02:12anchored up to the Northwest of the UK
02:14and that's what the situation is really
02:16for the rest of this week.
02:18The closer you are to the low pressure,
02:20the more showers you are likely to see.
02:23So yes, there is some rain crossing the Southeast
02:26on that weather front at the moment,
02:28but once that's out of the way,
02:30actually much of the South and East become dry.
02:33You can see now, look at the rainfall projections.
02:35Actually, the rain's gonna pep up tonight
02:37across Western Scotland,
02:39quite gusty conditions here as well.
02:41And if we just play through what's likely to happen tomorrow
02:44it's a day of showers,
02:45plenty of wet weather across Scotland,
02:47some showers further South across Wales,
02:50Northwest England and Northern Ireland.
02:52But the closer you are to that low,
02:54the more frequent the showers are gonna be.
02:56So quite a wet day in Western Scotland,
02:58whereas further South, it's gonna be dry.
03:00Another way to look at that is to put the totals on,
03:02the rainfall totals.
03:04Let's do the, let's fast forward through today
03:08and look at the rainfall totals for tomorrow.
03:10If we put the 12 hour totals on through tomorrow,
03:14you can see, and if we just tilt the map
03:17because we like the spikiness of it,
03:18you can see where the showers are coming in tomorrow.
03:20There's spikes showing where the showers are
03:22and it's Northwest Scotland closest to the low pressure
03:25where we'll see the most frequent showers
03:27coming and going throughout tomorrow.
03:28Whereas much of Eastern England and the South
03:31will actually probably stay dry tomorrow as a result.
03:35So it's a showery day tomorrow
03:36with the showers focused on the North and the West,
03:38much of the South and the East will be dry
03:40and fresher as well.
03:42We saw earlier that weather front that's moving through,
03:44it's a cold front.
03:45So behind that, we do actually have fresher air moving in.
03:49So the nights are going to be cooling off.
03:51It's going to be a good deal more comfortable
03:53as this cold front pushes its way through,
03:56but still it'll be quite warm in the sunshine tomorrow
03:59across parts of the Southeast.
04:02Temperatures could still get up to 23, 24 degrees
04:05across the Southeast,
04:06whereas temperatures elsewhere will be high teens
04:09or low twenties.
04:10So turning cooler, that's today, isn't it?
04:12Let's look at tomorrow.
04:13Similar though, although not as warm
04:15because the cold front has gone through.
04:16So 22, 23, so pretty much close to average
04:19across England and Wales, a little below average,
04:21particularly when those showers come into the North
04:24and the West.
04:25So it's a showery day on Wednesday.
04:27And then what we're looking at
04:28is weather systems out in the Atlantic, steadily moving in.
04:33So that low kind of fizzles out, pushes up,
04:35but another one takes its place.
04:37But then further South, we've also got this complication
04:39of weather fronts trickling in for Thursday.
04:41So that's going to bring more cloud and rain
04:43generally in from the West.
04:45So with the winds coming in from the West,
04:47that's where our influence is for the rest of this week,
04:51which means Western areas are going to see more cloud,
04:53more outbreaks of rain.
04:54Eastern areas are going to be driest.
04:57And just take it forward a little bit further
04:59because this position of this low
05:01is quite important for Friday.
05:03That could generate some fairly strong winds.
05:05Actually, if we zoom in,
05:06could get quite gusty across Scotland on Friday.
05:11With those isobars squeezing together,
05:13and particularly as the winds bounce over the mountains,
05:19could generate some lee gustiness.
05:20So we could see some quite strong gusts,
05:22particularly for the time of year
05:23across parts of Scotland during Friday.
05:25In fact, for the next few days,
05:27there's plenty of isobars across the North.
05:28So always quite breezy across the North,
05:30but in particular on Friday,
05:32with the winds just orientated,
05:33going perpendicular across the mountain ranges,
05:36that could generate some fairly brisk bounciness
05:39and some lee gusts,
05:40which we've talked about those before.
05:43So yeah, that's the weather for the UK
05:44for the next couple of days.
05:46As I hinted at,
05:47there are some signs of heat returning
05:49into the end of the weekend, early part of next week.
05:53Talk about more of that in a second.
05:54But first of all,
05:55let's go to the other side of the Atlantic
05:57because these things are not completely unrelated.
06:01Take the winds off.
06:03And yeah, we're going to be talking about this.
06:07This is Storm Debbie.
06:10It was a hurricane as it made landfall yesterday
06:13across the Northern parts of the Northwest of Florida.
06:16And now it's kind of just hanging around.
06:19It's drifting back out to sea,
06:21but it's moving very slowly.
06:23And if you put the jet stream on,
06:24you can see where the jet is at the moment up there.
06:27There's a long way,
06:28a long separation between this low pressure,
06:31this storm, this tropical storm,
06:33and the jet stream.
06:34They're not really interacting at this stage,
06:36but they are going to get closer
06:38and that's going to complicate things
06:39over the, towards the end of this week for sure.
06:42But for the time being,
06:44there's nothing to really shift this storm
06:47and it is dropping a lot of rainfall.
06:50When it hit, it arrived as a category one storm,
06:53gusts I think highest at 80 miles an hour, I think I saw,
06:55but it was still providing plenty of impacts
06:59as this video will show.
07:01I mean, it's,
07:03what did we do before we had trampolines
07:04showing how windy it was?
07:05But this video from TikTok from Live News
07:08showing some of the impacts from Florida,
07:10from Debbie, from yesterday.
07:11So torrential rain,
07:13there was also a big storm surge,
07:15which is where the storm literally picks up the water
07:17and raises the sea level effectively
07:19and floods the coastal areas.
07:20A lot of heavy rain,
07:22and it is the rainfall and the storm surge
07:25causing the biggest issues from this.
07:27So it's really a flooding problem from storm Debbie.
07:32The winds, yeah, pretty lively,
07:33but you know, it was a category one storm.
07:36The wind's not doing huge amounts of damage,
07:38but nevertheless, that rainfall, which will continue,
07:41and it's the slow moving nature of this storm
07:44that's gonna cause the issues.
07:46These are some of the rainfall totals we've already seen.
07:49So these are in Florida where the storm hit.
07:53That's in inches.
07:54So 16.56 inches,
07:56which is over 400 millimeters of rainfall.
07:59And quite widely,
08:00we've had two to 300 millimeters of rainfall already
08:03across parts of Florida.
08:05So for context,
08:06Essex gets less than 600 millimeters of rain in a year,
08:11and London's a bit more than 600 millimeters of rainfall.
08:15So yeah, we're talking at 400 millimeters already fallen,
08:19but the projections, okay,
08:21this was from yesterday
08:22and they've been toned down a little bit,
08:24but in this part of the world,
08:25as the storm slows down,
08:27we could easily see 20 inches of rain
08:29and the National Weather Service still highly think
08:31there is the potential for 30 inches of rain
08:33in some locations.
08:35So we could see 600 millimeters,
08:36maybe more in one or two locations.
08:38And again, just for equivalence,
08:41Essex received 600 millimeters throughout its entire year.
08:45So it is dropping a lot of rainfall.
08:47Slow moving storm is likely to cause some further flooding.
08:52Just want to highlight this tweet as well
08:54about the storm Hurricane Debbie.
08:55It made landfalls yesterday morning across Florida,
08:58making the fourth hurricane since,
09:00well, this century to make landfall in Florida.
09:03I thought this was interesting, Katrina 2005,
09:06because everyone associates Katrina with New Orleans
09:08and the devastation that that very powerful storm
09:11caused there with over a thousand deaths, I think,
09:14and billions of pounds worth of damage.
09:16But of course, before it got to New Orleans,
09:17it did cross over Southern parts of Florida
09:20near the other two other storms that actually,
09:23or hurricanes that made a landfall in Florida this century.
09:28That's not the only storm
09:30that we're talking about at the moment either.
09:32It's the only one that's really impacting land,
09:34but I thought I'd show you this satellite picture,
09:36which was tweeted by Met Office Storms.
09:40You should follow that Twitter feed as well
09:43if you're not doing it already.
09:44Obviously, follow the Met Office one,
09:45but we also have a Met Office Storms
09:46that Julian Hemming runs.
09:48And this was a satellite picture he posted earlier,
09:51because that is going down into, that's Mexico there.
09:55And this on the other side, so away from Debbie,
09:57but in the Pacific,
09:58actually had four storms going at once.
10:01I think this image was taken from yesterday.
10:02So very stormy in that part of the world at the moment
10:07with those tropical cyclones,
10:09tropical storms in the Pacific,
10:11and of course, Storm Debbie,
10:14which is potentially bringing huge amounts of rainfall,
10:18clearing away from Florida perhaps,
10:19but Carolinas in particular, South Carolina,
10:23gonna see devastating amounts of rainfall
10:26over the next 20 to four to 48 hours.
10:28It's a big, big news story, that one.
10:31And we'll continue to dominate the weather news,
10:34certainly for the next couple of days.
10:37What happens next?
10:38There is a bit of uncertainty about the path of Debbie,
10:41but it is gradually shifting its way northwards
10:44and may well interact with the jet stream.
10:47And that could, though not directly affect the UK,
10:50but it could certainly influence things for our weather
10:55as we go through the weekend
10:56into the early part of next week.
10:58For more on this,
10:59I spoke to Deputy Chief Meteorologist, Nick Silkstone.
11:04He joined me earlier on to discuss more about Debbie
11:07and its potential impact.
11:09Nick Silkstone, thank you so much for joining us
11:12here on the Deep Dive.
11:13You are a Deputy Chief Meteorologist
11:15here at the Met Office.
11:16Do you wanna give an overview of exactly what that entails,
11:19what that involves?
11:20I do a variety of positions.
11:22Today, I'm working on our sort of UK medium range bench.
11:26So I basically help narrate the main theme
11:29of the weather story for the UK
11:30from days three to days 30, in theory, into the future.
11:34Something I also do is I work on our global bench as well,
11:37as I have been doing over this past weekend.
11:39So that was the shift you were on yesterday,
11:42which kind of ties in,
11:42it all ties in nicely then with what we're gonna talk about
11:45because we're gonna be looking at
11:47what is now Tropical Storm Debbie
11:49and how that could be influencing our weather
11:52and potentially generate some heat
11:53for the UK for next week.
11:56Got quite a few complicated graphics to get through,
11:58which you're gonna guide us through expertly, no doubt.
12:00We'll start with this one,
12:02which is kind of the scene setter, isn't it?
12:05So this is the United States
12:07and talk us through what all the lines
12:09and the colors are here.
12:10Brilliant, so we're starting here,
12:12I should say this snapshot is approximately on Friday.
12:15Okay.
12:16So at some point on Friday,
12:17I can't remember the exact time of day.
12:18And I've got mean sea level pressure
12:20that people might know,
12:21pressure they expect at sea level,
12:22so it shows highs and lows.
12:24And this is our global model,
12:25a very coarse representation
12:26of the remnants of Hurricane Debbie
12:29in the mean sea level pressure field.
12:30On top of here, I've got the jet stream superimposed,
12:33the upper levels is what we call ice attacks
12:34of these color shades.
12:36And they're basically the further up the rainbow it goes,
12:38so towards orange means a stronger jet stream.
12:40And you can get the orientation of it approximately
12:42by following the peak in the contours.
12:44And then something called irritational winds.
12:46This is seen at very high in the atmosphere.
12:48This is where the wind is purely divergent
12:51or purely confluent.
12:53And that is represented the various vectors
12:55that you can see upon this image.
12:57Divergent obviously means the winds are going apart
12:59from each other.
13:00Convergent would be all coming together.
13:01So this is showing where the winds are kind of divergent,
13:04going away from each other.
13:05And this is high up in the atmosphere.
13:07So this is Debbie down at the surface,
13:10but the black arrows and the jet stream core here,
13:14that's all happening high up in the atmosphere.
13:16Absolutely.
13:17So the importance of this image,
13:19what it shows for us is,
13:21the exact location of the center of Debbie
13:22is probably not a primary importance actually
13:24in this event because it will have pumped up wherever it-
13:26And there is some uncertainty about exactly where Debbie goes.
13:29Absolutely.
13:30It will have pumped up lots of warm air
13:31on its eastern side against this tropical ridge.
13:34And then we have this trough,
13:35which you might just as well see
13:36as a little dip in the jet stream,
13:37which is already formed across Canada,
13:39which is gonna swing its way south and then eastwards.
13:41And that will start to pick up on Debbie,
13:44the remnants and all the tropical air
13:46is dredged up to the east.
13:47Once you have warm tropical air,
13:50something forward of a trough that causes ascent,
13:52you're gonna get basically lots of upwards motion
13:54in the atmosphere,
13:55leading to this strong upper level divergence
13:57that you can see as these vectors spreading out.
13:59So the air at the top of the atmosphere,
14:01or the top of the lower level of the atmosphere
14:03is basically just spreading out.
14:06Yes.
14:07And that impacts the jet stream.
14:08Absolutely.
14:09So in this case here,
14:10we've got already a reasonable thermal gradient.
14:12People might be able to see this little low
14:14in the northeast of the chart,
14:15which means fairly cool air coming down
14:17across Arctic Canada and Greenland.
14:19But this sort of mixing up a very warm tropical air
14:21to the top of the atmosphere,
14:22spreading it all out,
14:23is gonna basically increase the warmth
14:25in this part of the atmosphere.
14:27That will strengthen the jet stream
14:29because it feeds off temperature contrast,
14:31strong temperature contrast, strong jet stream.
14:33And it will also cause it to buckle or veer.
14:35And so the jet stream will become orientated
14:37from the northwest down towards the southeast.
14:39And that's gonna basically extend what we call a trough
14:42into the central Atlantic.
14:44So we can have a look at what we're expecting to happen.
14:47So this is now looking at just the jet stream
14:50and the surface pressure.
14:51By this stage, Debbie's kind of a diffuse mass
14:54and not as important anymore.
14:55But the key here is that change
14:57in the orientation of the jet stream.
14:59Exactly.
15:00That little bit of energy,
15:01the process is still going on at this stage,
15:03I should say.
15:04It's a Sunday, yeah.
15:05It's midnight into Sunday.
15:05Midnight onto Sunday.
15:07And here is our outflow.
15:08It's length in the jet stream,
15:09increased this thermal gradient,
15:10and our jet's up to 140 knots, so.
15:13Strengthening the jet stream and creating that.
15:16Yeah, northwest to southeast.
15:17So it digs down into the central Atlantic
15:19and creates a dip in the jet stream here.
15:21But of course, there are downstream consequences of that.
15:24Downstream effects.
15:25So we're over here, this is the UK,
15:27and that is likely to dip down and then push up there,
15:31which allows the UK to tap into.
15:34That's it.
15:35As this happens in this location now,
15:36this builds what we call a ridge forward of the feature.
15:40The ridge is gonna cause descent or subsidence
15:42of the air mass down across to the south of the UK
15:46and induce a slight southwesterly flow.
15:48All this means that it's opening up a larger area
15:51for some fairly hot, or even perhaps very hot conditions
15:54to develop across the southeastern part,
15:56at least the southeastern part of the UK,
15:58and the near constant later in the weekend
16:00into the early part of next week.
16:01It's a little bit like giving a flick to a rope
16:04and how that moves downstream.
16:06And the events that take place across the eastern seaboard
16:09of the United States over the next two or three days
16:12could bring us a shift.
16:14Absolutely, so these things,
16:16we actually, another complicated word,
16:18a roll of speed wave energy packet,
16:21but these can move around 30 degrees of longitude per day.
16:25So they can move very, very quickly,
16:27quickly through the pattern.
16:28So the influence here, this is only, you know,
16:30around about 75 west.
16:32You know, that can reach the UK in less than three days.
16:35As you say, it's whipping a rope.
16:36The actual things of the rope don't have to move,
16:38but the wave can travel faster
16:39than the individual elements.
16:41Absolutely fascinating.
16:42Okay, so we could, therefore,
16:44tap into some heat, potentially.
16:48And what's this showing here?
16:51So this is a projection.
16:53So this is for Canterbury, Kent,
16:55so very much the southeastern corner of the UK.
16:59And we're looking at this top one,
17:00which is an ensemble simulation,
17:01so multiple solutions.
17:03They have got what we call our perfect member
17:05who are in slightly more bold colors.
17:08This is the high res and then the control member.
17:10And then there's the spread.
17:11So subtle differences in the starting conditions,
17:14subtle different random things
17:15that happen during the run,
17:16sort of allows them to sort of gain things through height.
17:18So this is running the model many, many times.
17:20We've talked about ensembles before
17:22when it runs this ensemble picture of that.
17:24So you get all the different dotted lines
17:26or a different potential outcome,
17:28but they're all kind of showing the same thing in this.
17:30I hear.
17:31And this is showing the temperature at 850 hexapascals
17:33or roughly 1.5 kilometers up above the surface
17:37for Canterbury and Kent.
17:38And you can see that there's this jump that happens
17:41once you start to go through Saturday onwards.
17:43Probably this time of year,
17:44average is probably around this sort of 12, 14 degrees
17:48marked for the Southeast,
17:49because here suddenly we start to get
17:50this very warm temperatures.
17:52So these are the temperatures at 1.5 kilometers up.
17:55So there's 20 to 25 degrees on there.
17:57I'm not sure if you might be able to pick that up.
17:59And that's 1.5 kilometers up.
18:01So that's-
18:02Midsummer, as a rule of thumb,
18:03if everything's perfect,
18:04so no cloud, dry ground, light winds,
18:07inland from the coast,
18:08you can add approximately 15 degrees to this
18:11and that will give you an approximate maximum temperature.
18:14So once we're starting to see, you know, 20 degrees,
18:17it's giving us the chance.
18:18I should say UCMDF is the keenest solution on this so far,
18:21but it's given us the chance of reaching the mid 30s
18:24in parts of the Southeast next week.
18:26Okay.
18:27Early next week.
18:28Early next week, long way off,
18:29just a possibility at this stage.
18:30And there's quite a few of them that are, you know,
18:32a little bit lower than that,
18:34but it does show quite a strong signal
18:37that we're going to get some warmer air,
18:38at least across the Southeast.
18:40I'd say many of the features driving this,
18:41we've looked back on,
18:42and they all exist at the present time.
18:44You know, there's nothing too small scale,
18:46nothing too super complicated that's going to happen.
18:48So this signal has emerged quite a lot
18:50in the last 24 hours.
18:51I think we've probably followed it by like,
18:53we've probably gone like two thirds to all of this.
18:56So, you know,
18:56we're not coursing the absolute extreme extremes
18:58in our guidance and output,
19:00but we're now saying that, you know,
19:02reaching 30 degrees is more probable
19:04than not in this period.
19:05So there's a good chance of reaching 30 degrees
19:08early part of next week across the Southeast.
19:11That's, this is something interesting in itself.
19:13So this is kind of a similar thing.
19:15I just wanted to highlight this
19:16because this was,
19:17talk us through what's going on here,
19:18because I thought this was fascinating.
19:19Exactly.
19:20So exactly what we've just looked at
19:22with a few of the fields beneath it.
19:23This is run from ECMWF's analysis.
19:25This is what we call like a dynamical model.
19:27It runs through physics.
19:28It actually does equations to solve them.
19:31This is-
19:31Old school.
19:32Old school.
19:33This is the new kid on the block.
19:34So this is an AI version.
19:36Right.
19:37Which works, it's been trained on pattern recognition.
19:39So it's been given patterns in the past
19:41from ECMWF's past three analysis.
19:43And then it sees where those patterns have evolved,
19:46you know, in future in time.
19:48And this has been given the same analysis.
19:50So doing nothing physical, no equations,
19:52but just taking patterns forward.
19:53It has produced the forecast from that as an ensemble.
19:56Remarkably similar.
19:57So the AI forecast is very similar
19:59to the traditional forecast.
20:01Exactly.
20:02Other than the starting point, which is the same,
20:04the methods of getting there beyond
20:05are completely different.
20:06And they both end up with this, you know,
20:08hot spell in the South East,
20:10centred upon next Monday.
20:12Really interesting stuff there.
20:13And we don't want to leave everyone out.
20:15You said that it looks like the heat
20:16is going to be focused across the South East
20:19and potentially East Anglia,
20:20but perhaps a little further North as well.
20:21But this is showing what's happening in Western Scotland.
20:25So this is Stornoway.
20:27Unfortunately for the people-
20:28Well, maybe fortunately.
20:29Most people don't want 30 degrees.
20:31So maybe fortunately, but-
20:34Depends or not on your love of summery weather.
20:36But no, as we talked about the mid-Atlantic dredges
20:39of the warm air, the warm air will likely get
20:42into South Eastern parts of the UK.
20:43There's going to be a boundary.
20:45Unfortunately, if you live along that boundary,
20:47that's going to be what we call the frontal zone.
20:48Cloudy, outbreaks of rain running along it.
20:50It will meander, so it might not be stuck
20:52exactly over the same point every day.
20:55But the hints of warm air you get here,
20:56this is a very different scale
20:57as before the top of the scale was 24 degrees.
21:00Now it tops out at 15.
21:02And I see it's close to 10.
21:05Exactly.
21:05In high-rise.
21:06And for people, for people in Northwestern Scotland,
21:08not for, for people in Northwestern Scotland,
21:11this would likely be associated,
21:13the warm air there would be shelving over the cold air.
21:15It'd probably be cloudy, it'd probably be rainy.
21:16So this, you're not going to add 15 degrees on this
21:19and reach that at the surface, you know.
21:20This is going to be a muted mid to high teens.
21:22So there's a strong signal that the Southeast
21:25is going to see some heat early next week,
21:27but it's not going to be widely,
21:29well, it could be quite wide.
21:32The boundary is a big question mark, I guess,
21:33but it looks like the Northwest of Scotland
21:35isn't likely to see that kind of heat.
21:37We're not sure how far Northwest it's going to extend,
21:40but we're pretty confident.
21:41It's not always about as far Northwest as you can get,
21:43but it's not going to extend there.
21:45That's true.
21:45Okay, so that's good to show.
21:47And it just, actually I'll go back to that.
21:48Oh, where was it?
21:49Just to show that the AI model was also,
21:53also in pretty similar agreement there as well.
21:55So that's how things are progressing.
21:58Okay, so the potential for some heat
22:00and there is a bit of uncertainty, isn't there?
22:04Always is.
22:05We talked about how Debbie is going to impact things.
22:07That adds, if anything,
22:09a bit more uncertainty into the projections.
22:12This is quite telling, isn't it?
22:14Yeah.
22:15If people model watch,
22:16they'll have seen that this signal has jumped a lot
22:18in the last 24 hours as various things have come together.
22:20But I say we can map every feature where it comes from.
22:23They all look fairly well modeled now
22:25and everything, even the list from our model
22:27has gone in that direction.
22:28So we're fairly happy with it.
22:30This is ECMDF's ensemble.
22:31Again, we're looking up at 500 hectopascals here,
22:33so about six kilometers above.
22:35And we're looking at this broad area of troughing
22:37or this dip in the jet stream that's in the mid-Atlantic.
22:40And then this is the ridging.
22:41You can see that's across ourselves.
22:43Here I'm looking at midnight on Monday.
22:45And the colors here show, like normalize,
22:48how spread it is.
22:49So is the consistency within the ensemble more,
22:52or is it more consistent, less spread than normal?
22:55There are good bits that are in green.
22:56Or is there more spread or less confidence than normal?
22:59Yeah, bits that are in purple.
23:00It's almost a bit like confidence.
23:02We talked about confidence before as well.
23:03When there's more spread or more divergence,
23:05then you've got the purple,
23:06so it'll be less confident in what's going on here.
23:09But actually in this greener zone,
23:12you'd have more confidence in the forecast.
23:14Perfect.
23:15This is when the peak heat,
23:15our peak heat around Monday would get to us.
23:18And you can see that through this ridge axis
23:19where this is placed,
23:20there's at or even in places slightly greater
23:22than normal confidence in this zone.
23:25So, you know, a big part of the ensemble
23:28almost moved as one in small steps over 24 hours,
23:31but it's moved to quite a different solution
23:33from what we had 24 hours ago.
23:34But yeah, different modeling centers agree with each other
23:37that this is the most probable outcome.
23:39I said the actual thermostatic ECMDRF
23:41has gone even a little bit warmer.
23:43We've not quite gone that far yet.
23:44So it's putting all those things together.
23:46You know, we're now confident.
23:47Reasonable, just whereas 24 hours ago,
23:49there was a lot of uncertainty
23:51and Debbie was playing into that as well,
23:53as you'd expect.
23:54But actually it's quite remarkable
23:55how things have changed in 24 hours.
23:57It is that subtle difference of this pattern
23:59just being a little bit more amplified
24:01rather than being more zonal
24:02makes a difference between unremarkable temperatures
24:04and the chance of getting towards them
24:06or beyond them.
24:07Of course at this time of year,
24:08you know, extremes of temperatures
24:09are going to be particularly high as well,
24:10but it's because of the time of year.
24:13You've just literally sent me this
24:14before we came into the studio.
24:16This is a really interesting,
24:18you love focusing on this kind of thing,
24:20particularly when we get hot weather.
24:22I think it's really interesting
24:23because when we get hot weather,
24:26maybe I'm guilty of it as well,
24:27but the media often focus on
24:28where's the hot air come from.
24:30And we always say,
24:31it's come from the South,
24:31come from Spain, North Africa,
24:32but this is showing that this air
24:34isn't coming from there.
24:36What are we looking at here?
24:37So there's been a series of really good papers
24:39in the last 10 years
24:40that have really beyond all that
24:41conclusively proved that for most heat waves
24:45in Northwest Europe where we're situated,
24:48the sort of source of the heat
24:50comes not from warm air being advected in from Africa,
24:53but actually being compressed
24:54and squashed down to the surface.
24:56You can imagine it's like,
24:57almost like a bicycle pump.
24:59You know, when you compress the air within it,
25:01it gets warmer.
25:02This air that's been sitting around
25:03high up in the atmosphere,
25:04this is, these two lines equal
25:06the air that ends about 500 metres above Sussex
25:10early on Monday and 1,500,
25:12and then taking their trajectories back in time
25:13five days to where they are
25:15at the start of Wednesday.
25:15It's going back in,
25:16so it's now Monday,
25:18which is likely to see the peak of the heat
25:19across the Southeast.
25:20Where has that air come from?
25:22The air that is at 500 metres above the surface
25:27is in red, where it ends up at five,
25:29and the blue one is at 1,500 metres,
25:31so you can see where the air has come from,
25:33and the red, so that's what,
25:35five days before, so that's the kind of,
25:37the air has come from just off the coast of Canada there.
25:40Yeah, I ran these even further back,
25:43and the air remains in the mid-latitudes
25:45coming across parts of Canada
25:47and the eastern US,
25:48but the important bit here is that
25:50you can see all these little stars
25:51correspond to 12-hour gaps along the line,
25:53as you can see in the bottom here,
25:55but this warmth is effectively coming from subsidence,
25:57so that air that starts off is being compressed.
26:00Imagine if you compress, get lower in the atmosphere,
26:02there's more air sat on top of you,
26:03so the molecules move closer together,
26:05they vibrate more, that's temperature, yes,
26:07and this provides,
26:09this subsidence all happens across Biscayne and France.
26:12You can see at least two and a half
26:13or more kilometres of subsidence,
26:16and if that were to happen,
26:17a word that we,
26:18I never fancy a word, adiabatically.
26:20We're learning all the words to that, aren't we?
26:22It seems nothing mixes in, nothing mixes out,
26:24nothing leaves the system,
26:25so a closed system,
26:26that would be the equivalent of around about 25 degrees
26:29worth of warming for this parcel of air,
26:31and it's descent from the cold mid-troposphere.
26:33Right.
26:34Yeah, so this effectively puts a lid on the atmosphere,
26:37it produces warm air at very low elevations,
26:39meaning that when the sun comes out in the day,
26:42the sun only has to concentrate its heating
26:43on warming a very shallow layer of the air at the surface,
26:46whereas normally,
26:47when you see white, fluffy convective clouds,
26:49its heat's been concentrated over a much greater depth,
26:51and that allows basically more bang for your buck
26:53with the sun.
26:54You get more, higher temperature
26:56for the same input of energy.
26:57Exactly, and there is gonna be a little bit of mixing.
26:59This air is very warm itself,
27:01so this air will also mix into the surface air
27:03to some degree,
27:04but that's a good way of thinking it.
27:05It's almost like putting a lid on the pan,
27:07a very strong, well-sealed lid on the pan,
27:09and concentrating that warming down at the surface,
27:11so in this case, subsidence and the compression.
27:14Sure, you might not be able to pick it up,
27:15but there's lots of stars in there,
27:17so that's the crucial fact,
27:18so that's the point at which it's really heating up,
27:19is it's over France and Biscay,
27:21because that's the time period
27:24where it's getting lower and lower,
27:25and also heating up and moving across over those five days,
27:30but it's concentrated there for a couple of days.
27:32Exactly, the last three days,
27:34you could probably say to the right of my hand,
27:36that's where all this subsidence
27:38in the last three days from there
27:39is happening across the Bay of Biscay, France,
27:42and then just in the last 12 hours,
27:45wafts up to ourselves in the UK.
27:47Right, yes, actually that's interesting,
27:48it's that last 12 hours where it does move northwards,
27:51so really fascinating stuff,
27:53how that heat is likely to build,
27:56and the air isn't coming from Spain or North Africa,
27:59it's coming from off the coast of Canada,
28:01which is slightly counterintuitive,
28:03and then, I guess the next question is,
28:06how long's it gonna last,
28:07and this chart would suggest perhaps not that long,
28:10so what are we looking at here?
28:11So by this point, I just have to check the date,
28:13I think we're through to next Tuesday.
28:15Yeah, Tuesday night, Wednesday morning.
28:16Perfect, next Wednesday, so by this point,
28:18the dip in the jet stream
28:19that was originally in the mid-Atlantic
28:20is migrating its way eastwards,
28:22and you can see where it's quite strong,
28:23what we call zonal flow,
28:24this is 100 plus knots on its southern side,
28:27this basically means that we're likely
28:28to displace the hot air eastwards,
28:31couple where this would be Atlantic frontal zones,
28:33rain, you know, some relatively deep areas
28:35of low pressure are possible
28:36in the middle part of next week,
28:37so that would be all shunted eastwards,
28:40exactly how long it lasts,
28:41I think certainly Monday looks like the peak of the heat,
28:43could last into Tuesday,
28:44but once you get to Wednesday and beyond midweek,
28:46the sign is that the heat will be very much displaced
28:48away to the southeast,
28:49and it'll become cool, unsettled, rain.
28:52Back to the summer that we've got used to,
28:57and just one final chart, that's this one,
28:59that's kind of showing the same thing,
29:00although, as we saw earlier,
29:02there's more purple on this,
29:04suggesting we're less confident in the position of it,
29:08but you'd expect that
29:09because it's further ahead in time as well.
29:10Yeah, they normalise it,
29:11so it shouldn't change too easily,
29:13but you can see that even upstream
29:14where there's normal or even high confidence,
29:16this is what we call a very zonal pattern,
29:18you know, these geopotential height lines
29:20are running east to west along the lines of latitude,
29:24so this suggests to me that this pattern
29:26is going to progress, you know,
29:27and there's confidence in this part of it
29:28that it will progress,
29:30and if that progresses, it all gets swept out of the way.
29:32It all gets shifted up,
29:33and the heat is gonna be located more,
29:36shifted into more central parts of Europe,
29:38that's the more likely scenario,
29:40so a hot spell is quite likely,
29:44certainly, almost certainly
29:45across the south-eastern East Anglia,
29:47where the boundary is open to doubt,
29:50and that's not unusual at this kind of time range,
29:53then it probably won't last into the middle of next week.
29:57Yeah, the humidity will pick up
29:59probably on Sunday across southern parts,
30:00so probably first quite a lot of low cloud,
30:02but the substance I've mentioned
30:03will make the cloud layer ever shallower,
30:05which will let the sun get to work and break it up,
30:07so Sunday's probably the first chance
30:09that we're gonna get,
30:10you know, when it brightens up inland,
30:12high 20s, and a small chance of reaching 30.
30:15Monday, then, once we've got the stuffy flows
30:17we saw with those backwards trajectories,
30:19which come from the continent,
30:20or expect to come from the continent,
30:21that air mass is gonna have a somewhat drier source,
30:23so we should have less low cloud,
30:25less low clouds to the start of Monday,
30:27and that's more probable, then,
30:28that we'll heat up quicker,
30:30as well as having that hotter lid on.
30:33Okay, well, some people will be quite upset
30:37that the heat is gonna come back.
30:38I know a lot of people don't enjoy the heat,
30:40and this could be, you know,
30:42some of the highest temperatures
30:43that we've seen over the summer.
30:44Still a lot to play for.
30:46Obviously, the developments of Debbie,
30:48you know, still add some uncertainty,
30:50even though confidence has grown over the past 24 hours,
30:52so certainly something we'll be keeping an eye on.
30:54Yeah, and just the one final thing to play for,
30:56when the heat breaks down as often as the case,
30:58thunderstorms will be a word.
31:00As we saw last week, yeah,
31:02that could be a crucial factor, as well,
31:04so an awful lot going on.
31:06Nick, thank you so much for joining me and us here today.
31:11I know you're a busy guy,
31:12so thank you very much for taking your time
31:14to come and join us on today's Deep Dive.
31:16Huge thanks to Nick for joining me earlier.
31:19Very, very busy, as well as a very,
31:21very clever chap here at the Met Office.
31:23Now, he is not the only guest
31:25that we've got on this week's Deep Dive,
31:27because last week, we were visited by Clive Bailey,
31:30who is the flight director for the Bristol Balloon Fiesta,
31:34and a very experienced balloon pilot.
31:37He came to the Met Office,
31:38so we needed someone to talk to him
31:41who knew a thing or two about hot air.
31:43So, Aidan had a really interesting interview with Clive.
31:47There's a full-length interview available on YouTube.
31:51We'll put the link up in a moment,
31:53but here's a little snippet
31:54from Aidan's chat with Clive Bailey.
31:57One thing I noticed when I went ballooning,
32:00it was the first time I'd seen a balloon up close,
32:02you know, because normally people see them from a distance.
32:05You don't often get the opportunity to see them up close,
32:07and what surprised me was how big they are.
32:11So, a big balloon that takes pilot plus 16 people
32:14is the sort of biggest passenger rise balloons
32:17we have in the UK.
32:19That balloon's about 90 to 100 feet high
32:22and about 70 to 80 feet wide
32:24and holds 400,000 cubic feet of air.
32:28Maximum temperature at the top of the balloon
32:30you can get into is 120 degrees.
32:32Wow.
32:33And then we do a calculation.
32:34So, the weight of the balloon, the weight of your fuel,
32:37your weight of your pilot,
32:38the weight of all your passengers.
32:39For a big balloon of 400,
32:41it's going to come out round about two tonnes.
32:44That sort of figure.
32:45It might be 1,700, it might be 2,200 kilos,
32:48but about two tonnes.
32:50Now, what happens when the temperatures go up?
32:54So, the cutoff point really is 25 degrees,
32:58and then you have to start seriously looking
33:00at your load calculations,
33:01because once you get up to 28 degrees,
33:03instead of taking 16 passengers,
33:06you might have to drop two passengers,
33:07because bearing in mind,
33:09we're working on the internal temperatures
33:11versus the outside temperature.
33:12So, the hotter it is outside the ambient temperature,
33:15the hotter we've got to get the balloon.
33:17Would you say that that is the most dangerous thing
33:20that you might face as a balloonist?
33:21It's the rising air currents?
33:24So, the things that we look at in a forecast,
33:28apart from your winds,
33:29if it's too windy, you're not going to take off.
33:30If the wind picks up when you're flying,
33:33you're just going to have a faster landing
33:35and you'll have a dragged landing.
33:36Well, most pilots can take that.
33:38The one that we don't like is instability.
33:41So, generally, if there's a thunderstorm in the forecast,
33:45even a prop 30 of a thunderstorm,
33:47we don't go flying,
33:48because that's an indication it's unstable
33:50and what could happen.
33:52One of the biggest challenges must be,
33:54you know, in this country, precipitation.
33:56Yeah.
33:56So, would you never fly if there's the chance of rain?
34:01Is that how it...
34:02The trouble is, it's pretty miserable
34:03putting a balloon away when it's wet.
34:06It doesn't do the fabric any good
34:06because you'll be almost boiling the water on the fabric.
34:09And then it's twice the weight.
34:11You try putting a wet balloon away, it's just not fun.
34:13And then also your visibility goes down.
34:15So, rain really, for us, is a no.
34:17If you get caught out in a shower,
34:19it's not the end of the world.
34:20It's fine, but it's just not quite as pleasurable.
34:23I have been in a balloon in Wales
34:25and we got caught out
34:26and we all had a hot shower in the balloon
34:28because the top of the balloons are flat
34:30and the water sits and sits and sits.
34:32And then the parachute valve,
34:34which is a big valve at the top of the balloon
34:35that you can let the air out with,
34:37just leaks and it just tumbles inside.
34:39So, it's warm.
34:40So, it's quite pleasant.
34:42Put all your bags away, put your instruments away.
34:45You know it's coming.
34:46We touched on the wind and how that varies with height.
34:49And you, first of all,
34:53when you're taking off from the surface,
34:55you need the winds to be a certain strength, don't you?
34:57What's your kind of upper limit at the surface?
34:59Well, the legal certification for balloons
35:03is 15 knots on takeoff.
35:06Most balloons you wouldn't get in the air at 15 knots
35:08because it'll be dragging the vehicle
35:10that you're tied down to and all the rest of it.
35:11So, really, calm on the surface is absolutely ideal.
35:16Up to five knots is fine.
35:18Six or seven knots gusting 12 is very difficult
35:21and you've got a bit of a handful.
35:23Would that, if you're going up
35:24and you've got such a pronounced wind shear,
35:27your balloon is tall, right?
35:29You said 100 feet or so.
35:31It literally starts to tilt.
35:32It starts to tilt, yeah.
35:34And balloon pilots don't like wind.
35:35You don't like wind in your face
35:36because you know you're entering something.
35:39And then generally you go up through that level of fast wind,
35:42go up above it and it stops.
35:44And you get the opposite,
35:45knowing you've got to come back down again.
35:48Yeah, yeah.
35:49So, it's not so bad if it's at 800 feet,
35:53but if it's at 200 feet above the surface,
35:56then you've just got to be a bit careful
35:57coming back down through it
35:58because very often it's going to knock a lot of your hot air
36:01out of your envelope.
36:02So, you're going to come down underneath.
36:03But you use the variation of the winds,
36:06as we've already touched on,
36:08to help steer a balloon on a route out.
36:11That's right.
36:12We've got, from Ashton Court in Bristol,
36:14which is the sort of centre of ballooning in this area,
36:17we've got farms out between Bristol and Bath
36:21that we know are extremely friendly.
36:23And if we can get those fields,
36:24those are the ones we're going to aim for.
36:26As soon as we take off, off we go.
36:28And we've got quite a few farms in Bristol
36:31that we've done that to over the years.
36:32And the farmer said,
36:34you know, can I have a break for a year
36:35because you keep waking me up at eight o'clock
36:37or six o'clock in the morning
36:38and I just want to have a break.
36:39So, yeah, of course you can, that's no problem at all.
36:41Yeah, he's sick of getting champagne at six in the morning.
36:45Or doesn't drink it.
36:48And there is loads more in the full interview with Clive,
36:52including a solar-powered balloon expedition,
36:56also his trip across the Atlantic in a balloon,
36:58and some interesting techniques for measuring the winds
37:01while you're in a balloon as well.
37:03You can watch the full video here.
37:05And also, last week, did you know it was our birthday?
37:09170 years of the Met Office,
37:11and there's more about that in this video here.
37:14Thanks for watching this week's Deep Dive.