Deep Dive 08/10/2024 - Latest in-depth look at global and UK weather
This is an in-depth Met Office UK Weather forecast for the next week and beyond. A major hurricane is heading towards Florida whilst an ex-hurricane affects Europe. Bringing you this deep dive is Met Office meteorologist Aidan McGivern.
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00:00Hurricane Milton transformed from a tropical storm on Saturday to a Category 5 hurricane on Monday.
00:08It was the second fastest intensifying Atlantic hurricane on record and is now expected to hit Florida as a major hurricane.
00:17The second major hurricane to hit Florida in less than a month.
00:22Meanwhile, ex-hurricane Kirk slams into Europe, avoids the UK, but leads to colder weather as it clears away across much of the country.
00:33And how's it looking into the weekend and next week?
00:38Plenty to cover in this week's Metal Fist Deep Dive, exclusive to the Metal Fist YouTube channel.
00:43If you haven't already done so, please do hit subscribe so you never miss one of these updates.
00:47They come out every Tuesday and they are our regular in-depth look at meteorology in the UK and around the world.
00:54There's plenty to talk about around the world at the moment.
00:58And eagle-eyed viewers will have noticed that I've swapped sides.
01:03We used to present these on that side. That's where the buttons were.
01:07We've switched the buttons to put them on this side.
01:10And there's a slightly new interface, a slightly new design, which will, currently, very much work in progress,
01:17but which will hopefully in the next few weeks and months allow us to do even more, show you more things and be even more interactive.
01:25And, well, let's just say it's the first time I've been using it in this kind of presentation.
01:31So anything could happen. It's worth staying tuned just to see if anything does indeed go wrong.
01:37Now, first of all, Hurricane Milton. This shows the satellite imagery from Saturday to Tuesday morning.
01:45And it shows the speed of intensification.
01:49Truly powerful system by the time it reached the Yucatan Peninsula on Monday evening.
01:57At that point, sustained winds were 180 miles an hour and the central pressure was 897 millibars.
02:06And that central pressure made it the fifth strongest Atlantic hurricane on record by pressure.
02:12It was also the joint sixth hurricane in the Atlantic on record for wind speed and is now expected to move northeastwards
02:24and weaken slightly but still hit Florida as a very powerful major hurricane.
02:31This is the official track from the National Hurricane Center.
02:34And worryingly, it does take Milton into Florida as a Category 3 hurricane.
02:42Sustained winds on landfall of 125 miles an hour.
02:47It then crosses the Florida Peninsula as a hurricane and leaves the other side, clears the east as a Category 1 hurricane
02:55before weakening quickly as it moves into the Atlantic and moves towards Bermuda.
03:01But, yeah, it's at the moment oscillating between a Category 4, high-end Category 4, low-end Category 5.
03:09So it's a very, very powerful hurricane.
03:12And it was the above-average sea surface temperatures in the Gulf that led to this very rapid intensification that we saw throughout Monday.
03:2024 hours it went from Category 1 to Category 5 and that's what made it the fastest intensifying,
03:27or the second fastest intensifying hurricane on record in the Atlantic area since, second fastest intensifying,
03:36got to get my facts right here, second fastest intensifying hurricane on record.
03:41The fastest being Hurricane Wilma in 2005.
03:45So truly a very, very powerful storm.
03:49And not only will the winds be destructive, but there's going to be the risk of widespread flash flooding as a result of the rainfall.
03:58This is the expected rainfall from the National Hurricane Center.
04:02And it shows areas of 300 to 400 millimeters of rain.
04:07They're showing it in inches.
04:09That's the scale there if you can see it.
04:12Obviously the really heavy rain out in the sea there, but still over Florida,
04:17300 to 400 millimeters of rain in just a day or so leading to widespread flash flooding, river flooding, and so on.
04:25And although the winds will weaken slightly, so it will go down from Category 4, Category 5 to Category 3,
04:34it's expected to grow in size.
04:36And when these hurricanes get larger, the risk of storm surge is greater.
04:42They churn up even more water.
04:44And we saw that with Hurricane Helene, of course.
04:47That hit the Big Bend area of Florida.
04:49This area came up from the south, so a slightly different track, but still hit this area with a storm surge of 10, 15 feet.
04:57And expecting similar storm surge there for the Tampa Bay area, 10 to 15 feet.
05:02That's where the hurricane is expected to move through on Tuesday, well, no, Wednesday night, I beg your pardon, early Thursday.
05:12So, yeah, 10 to 15 feet.
05:15Really worrying impacts for Florida and just the second major hurricane to hit Florida in less than a month.
05:24So all the official updates, you can get those through the National Hurricane Center.
05:29They are the authority on hurricanes in this part of the world.
05:33And, of course, we'll be monitoring it as well here at the Met Office and keeping you updated.
05:38Now, later, I'll mention how ex-hurricane Milton next week could cause some uncertainty with our own weather.
05:47But for now, we've got another ex-hurricane to think about.
05:51And that is ex-hurricane Kirk.
05:54And what I did last week was I saved the model data from hurricane Kirk because I thought it showed a really interesting transition from a hurricane to an ex-hurricane.
06:04And this is what's playing on the screen at the moment.
06:07There are a number of differences from hurricanes to ex-hurricanes.
06:11And so I did a video that you can find on the Met Office YouTube channel explaining these differences between tropical cyclones and extra-tropical cyclones.
06:20Extra-tropical cyclones are those cyclones that occur outside of the tropics.
06:26Hurricanes are tropical cyclones.
06:29And there are a number of differences in terms of where they get their fuel from and how they are structured.
06:34So I went through those in this video that you'll be able to find on the Met Office YouTube channel.
06:39But this shows one of the differences really well.
06:43And that is the temperature gradient around the storm.
06:48Now, in hurricanes, as they form in the tropics, there's little horizontal temperature gradient.
06:53It's warm across the whole area.
06:57But as hurricanes move into the extra-tropics or the mid-latitudes, they increasingly develop a temperature gradient.
07:06Now, we are familiar with temperature gradient in areas of low pressure ourselves because we call them weather fronts.
07:13When you get this steep temperature gradient from one area to another area, two different air masses colliding, we mark the boundary with a weather front.
07:23So we are familiar. Virtually all the low-pressure systems that we come across in the UK have some kind of weather fronts.
07:30Cold fronts, warm fronts, occluded fronts.
07:32So we're always banging on about weather fronts.
07:34Hurricanes don't have weather fronts. They don't have that horizontal temperature gradient.
07:38But as they move north, they encounter cooler seas.
07:41They weaken unless they move over areas where there is a sharp temperature gradient and or a powerful jet stream.
07:50And it's those things that can cause additional energy.
07:53Those things fuel mid-latitude areas of low pressure.
07:57So hurricanes fuelled by very warm seas in the tropics.
08:01As hurricanes move north, they move over cooler seas and they weaken significantly.
08:06But the kinds of lows that we get at our latitude, they're fuelled by the jet stream and they're fuelled by temperature differences.
08:14And what you're going to see is as Kirk moved over cooler seas, it increasingly developed this temperature gradient.
08:22And on Monday, it went from officially being a hurricane to an ex-hurricane as it developed a different kind of structure and weather fronts.
08:32And it's those weather fronts that are moving into Spain, Portugal and France over the next couple of days.
08:37Really, you've got cold air. You've got all this warmth pushed north.
08:43And then you've got cold air coming in from the north and west.
08:48And that develops a cold front and you've got the warm front with the higher humidities that are from the tropics.
08:55And you get this enhanced temperature difference.
08:57So one of the key differences is the temperature gradient across the storm.
09:03That's what marks the difference between a hurricane and an ex-hurricane.
09:06Another key difference is the spread of the winds.
09:10Hurricanes, as you can see, this is the wind gust graphic.
09:13And the darkest colour, the strongest wind gusts in the hurricane, are focused right next to the eye of the storm.
09:21So you get a very small area of very intense hurricane force winds.
09:28Now in Milton at the moment, I think it's around 30 miles, or at least it was on Monday night, 30 miles of hurricane force winds surrounding the eye.
09:37But it can be a very narrow area surrounding the eye of very intense winds.
09:42As hurricanes move north and they transition to the ex-hurricanes, what's more typical of mid-latitude lows is that those winds get more spread out.
09:52So you get stronger winds over a larger area.
09:54The low pressure system itself expands, but the winds aren't as intense.
09:59And they're not necessarily focused around the central low pressure.
10:02And they're more asymmetrical.
10:05So in a hurricane, you've got much greater symmetry around the eye of the storm.
10:10Then as those winds spread out, they can be a lot more asymmetrical.
10:14Typically, with these mid-latitude lows, you get the strongest winds on the southern flank of the low.
10:20And that's what we're seeing.
10:22So how is ex-hurricane going to affect...
10:27Let me just get the right graphic here.
10:30I told you it would be a learning experience for all of us.
10:33How is ex-hurricane Kirk going to affect Europe?
10:37Fortunately for the UK, at least, it is taking a southward shifted track.
10:42The jet stream is very south shifted at the moment.
10:45That is carrying Kirk our way.
10:48Now what I'm going to show you here is the accumulated wind gusts.
10:52This is the maximum wind gust as you go through Tuesday into Wednesday and Thursday.
10:59So you can see basically the trail of strongest wind gusts as Kirk moves into Iberia and France.
11:08There's Kirk.
11:10And at the time of recording, just moving north of the Azores.
11:15And then if we just move this forward, and you can see the strongest winds moving through during Wednesday.
11:24And then weaken considerably as this low pressure system moves into central parts of Europe.
11:31Still has a fairly deep low, still with some heavy rain in places.
11:35But here's the strongest sway of the wind.
11:37So these are the 50, 60, and in some places, so northern parts of Spain, parts of Portugal, 70 mph wind gusts during Wednesday.
11:47So yeah, that's the sway, the very strong winds.
11:51There was a risk looking at some of the different tracks from the model output this time last week.
11:57There was a risk that those winds would affect southern parts of the UK.
12:00But thankfully for the UK, it's France, Spain, Portugal that will bear the brunt of the strongest winds.
12:07And that's why Meteo France have named this.
12:12They've named it Storm Kirk.
12:14When these things come across as ex-hurricanes, they typically keep their name.
12:18So Meteo France have named it as Storm Kirk.
12:21No longer a hurricane, of course, but still has a very wet and windy system.
12:26And expected to bring some very heavy rainfall in places as well.
12:30Now this is a similar thing I'm going to show you.
12:32And it's accumulated rain.
12:36So how the rain builds up, basically, during the next few days.
12:40And as Kirk arrives during Wednesday, you can see this area, this swathe of heavy rainfall.
12:4850-100 mm across northern France.
12:51And more than that across the south of France, northern Italy as well, over the mountains of course.
12:55Parts of Portugal and Spain.
12:58So more than 100 mm, up to 200 mm perhaps over the mountains as Kirk moves through.
13:04So the UK has been spared because of that south shifted track of Kirk.
13:09The very worst of the wet and windy weather.
13:11However, the UK won't be completely unaffected by Kirk because there will be impacts on our own weather.
13:18So I'm going to take you through the jet stream at the moment.
13:20It's quite an interesting setup.
13:22There's two streaks of the jet stream there at the time of recording.
13:26There's one that's south shifted compared with normal.
13:29We've talked a lot about south shifted jet streams recently.
13:32And that's because a climatological position or a more typical position for the jet stream is somewhere just to the north-west of Scotland.
13:40But frequently we've seen the jet stream much further south than that.
13:43And that's what we're seeing at the moment.
13:45That's why, at the time of recording, we've got low pressure sitting across the south-west of England, south Wales as well.
13:52And some very lively heavy showers moving in around that low.
13:57Slow moving, thundery downpours, hail in places during the rest of Tuesday.
14:02More details on that in our short-term forecast, of course.
14:05There's no point in me talking too much about that because by the time a lot of you watch it, it will be all over.
14:11But there is a weather warning in force.
14:13And so, yeah, full details on our YouTube channel for all of that.
14:17But that's all caused by this south shifted jet stream.
14:22Then looking out in the Atlantic near the Azores, which are there, an even further south shifted jet stream.
14:28And that's what's picking up Kirk and taking it during Tuesday into Wednesday on that track that mostly avoids the UK.
14:42But, and here's the important thing, because the jet stream is quite far to the south, as Kirk moves away, it opens the door to Arctic winds.
14:55And you can see that temperature plunge through Thursday.
14:59So let's turn on the maximum temperatures for Thursday.
15:01Thursday is the coldest day widely across the UK.
15:05There will be some sunshine out there, just a few showers across the north and east of the UK.
15:09But you can see how high those temperatures are, 9 to 12 Celsius widely.
15:13And feeling even colder when you add in the effect of the wind chill.
15:16So let's take a look at the wind chill.
15:18Let's go forward to Thursday there.
15:21And Thursday afternoon, you can see, what, 6, 7 Celsius or so.
15:28That's what it's going to feel like.
15:30Not only that, but overnight temperatures are going to drop as well.
15:34So this shows the minimum temperatures for Edinburgh.
15:38Edinburgh, that's the minimum temperature trend through the next few days, down to the low single figures.
15:43Glasgow, for example.
15:45Stormwake. Temperatures are a bit up and down as we head into the weekend.
15:50And that's because there's a little bit of a complicating factor emerging.
15:56Now, we start off Thursday with those northerly winds.
16:01So sunny spells, showers, those showers pushing into the north and the east, as well as northwestern parts of the UK.
16:09The showers will be turning wintry over the Scottish mountains.
16:12So we can expect some sleet and snow, even down to 300 or 400 metres.
16:16But mostly any lying snow will be 500 or 600 metres and above.
16:20Still, though, some significant snow expected during Thursday into the start of Friday over, for example, the Cairngorms.
16:28So above 500 or 600 metres, you can expect 5 to 10 centimetres of snow.
16:33Really significant for the start of October.
16:36At lower levels, of course, it will be rain, perhaps some hail showers.
16:40But by Friday, some mild air is on the way.
16:44Because what happens is this slice of jet stream emerges in the Atlantic and starts to move towards northern parts of the UK.
16:54Now, in the south, it stays relatively chilly on Friday.
16:59But further north, we've got this slice of less cold air arriving.
17:04And by Saturday, that's also going to lead to some showery rain across parts of Scotland, for example,
17:12perhaps fringing later on into northern parts of England and Northern Ireland.
17:17This slice of jet stream, though, is causing a few issues in the computer modelling, some uncertainty.
17:23Now, in the Met Office output, it just leads to some showery rain.
17:27But there are some computer model simulations that cause this slice of jet stream to spin up a relatively deep area of low pressure
17:37and cause more widespread wet and windy weather across northern parts of the UK on Saturday.
17:41So that's something that we'll keep a close eye on.
17:44Further south, we keep a ridge of higher pressure, although, again, a fly in the ointment is this low pressure,
17:50which some computer model simulations push a warm front up into southwestern parts to give some cloud and patchy rain.
17:58So, yeah, a few details to iron out for Saturday.
18:02There's the chance of showery rain in northern parts of the UK, especially Scotland,
18:07and the smaller chance, the lower likelihood of more widespread wind and rain in the north and northwest.
18:15Meanwhile, in the south, it's most likely going to be a fine day on Saturday,
18:19but there is that chance of a warm front emerging to bring some cloud and patchy rain.
18:23By Sunday, no matter what happens with those systems, there's good confidence that a ridge of higher pressure will build across the UK, settling things down.
18:33Meanwhile, out in the Atlantic, these areas of low pressure, it gets messy, basically.
18:42And this is an increasingly strong jet stream.
18:47So we've got 130 to 140 mile per hour wind speeds on that jet stream.
18:53Within it, we've got these areas of low pressure.
18:56But meanwhile, this is, by this stage, ex-Hurricane Milton, weakening considerably as it moves over the cooler waters of the Atlantic.
19:07And down here, we've got ex-Hurricane Leslie.
19:11So Leslie also weakening as it moves north.
19:15And those two ex-tropical systems are likely to bump into the jet stream, this powerful jet stream,
19:22and just add to the uncertainty for next week's weather.
19:25Because how they interact with the jet stream and how the jet stream interacts with those
19:30will determine how the jet stream affects the UK's weather through next week.
19:36Now, there are a lot of model simulations that have low pressure sitting just to the northwest of the UK, to the south of Iceland.
19:46And this is the most likely weather pattern for Tuesday, next week, so a week's time.
19:52The second most likely weather pattern for the same day has that low pressure sitting slightly further south.
19:59And rather than southwesterlies, we've got more southerlies for the UK.
20:05Still the wettest and windiest weather to the west of the UK and the northwest, drier to the east.
20:12And you can see these plus 0.7, plus 0.8 numbers on the map, indicating that it's going to be warmer than average.
20:20But those subtle differences in the two most likely weather patterns,
20:24remember these weather patterns are the result of all the different computer model simulations from the European model,
20:32the American model, the Met Office model, and those simulations are summarised in those two most likely weather patterns.
20:40But when we look at the detail, this is from the operational run of the European model,
20:46and it shows something a little bit differently.
20:48So this is from the higher res run rather than all the different lower resolution simulations that we see.
20:55This shows lower pressure further to the west, much more of a direct southerly wind,
21:01and the rain in the west staying away from the UK.
21:03So this is the UK here, if you can't see it that clearly in the camera.
21:06And this plume of wet weather moving into the southeast because you've got this southerly flow.
21:14And in this simulation, we've got higher pressure exerting itself over Scandinavia.
21:20Meanwhile, the main run of the American model shows something similar.
21:26The rain largely kept to the west of the UK.
21:28Again, this is Tuesday of next week.
21:30And these continental plumes are more of a southeasterly airflow rather than a southwesterly.
21:35So many parts of the UK dry, higher pressure over Scandinavia again,
21:39but the chance of some rain moving up from the continent to affect southeastern areas.
21:43So these are the kinds of uncertainties we're dealing with.
21:45And the reason the weather is uncertain for next week is because of the interaction between those ex-tropical systems and the jet stream.
21:55It's a week away, so we'll have to see how Milton moves through flora, comes out the other side, moves into the Atlantic,
22:02moves over colder waters, interacts with the jet stream.
22:05Leslie then joining in as well.
22:07And how those very powerful but very small systems interact with the jet stream will determine how amplified the jet stream is.
22:14Now, if the jet stream is very amplified, by that I mean it's wriggly,
22:18then we end up with this kind of pattern where the rain largely stays out to the west and we get a direct southerly or southeasterly.
22:25If the jet stream is a bit flatter, then you get more progression from the Atlantic.
22:29So these systems sweep through.
22:31So lots of uncertainty for next week.
22:34And we'll be covering that, I'm sure, in much more detail in the 10-Day Trend tomorrow.
22:39That will be done by Alex Deacon.
22:41So stay tuned for that.
22:43Hopefully, you'll have more insight and we'll have a clearer idea of how these systems will affect the UK through next week.
22:49Although I suspect, given that the tropical systems are the key in determining the amplitude of the jet stream,
22:58it might be some days before we have a much more confident idea of what's going to take place through next week.
23:04But most likely, unsettled towards the west, higher pressure over Scandinavia and some sort of slow moving pattern in the vicinity of the UK.
23:16But, yeah, like I say, we'll be covering that in much more detail in the 10-Day Trend tomorrow.
23:21I've talked for long enough today.
23:23I hope you've enjoyed it.
23:25Thank you for sticking with the new touchscreen interface.
23:30It will take us some time to get to grips with it, I'm sure.
23:33But let me know if you've got any comments or feedback about that or anything else you'd like to see in these deep dives.
23:40We'll be here once again doing the same thing next Tuesday.
23:43Thank you for watching. Bye bye.