the headlines: a major hurricane travelling towards texas has developed into a category three storm, with sustained winds of 215 kilometres per hour. a major disaster has been declared. south korea's military says north korea has fired several short—range missiles into the sea off its eastern coast. the us says they did not pose a threat either to guam or north america. a man has been shot and killed by security forces in brussels after reportedly attacking soldiers with a machete. one report said two soldiers had been lightly wounded. and two of the world's biggest fighting stars have completed their weigh—in ahead of saturday's fight. the boxer floyd mayweather and the mixed martial arts star connor mcgregor will go head to head in las vegas. now on bbc news, weather world. this time, the bbc weather team take to london's rooftops with urban forecasters to explore why city climates are so different that on the coast or countryside.

this time on weather world we are the highest point of the uk's is the city, uncovering the secrets of urban weather. and finding out why heatwaves hit cities and those of us who live in them the hardest. we ta ke to who live in them the hardest. we take to the rooftops of london to see just how man—made environment can change the weather forced what are you hoping to achieve in the future? when we do weather forecasts we will give more detailed forecasts so we will give more detailed forecasts so there will be differences between different parts of the city. also on weather world: out of nowhere. a view of mudslides and storms, as we ta ke view of mudslides and storms, as we take a meteorological view of the world. scorching summer in southern europe and the deadly consequences of wildfires that rage out of control. watch the birth of a flood

as it surges down a dry riverbed to the floods that sweep away everything in their path and the disaster they cause. plus, everything in their path and the disasterthey cause. plus, cold comfort. the blanket response to melting glaziers in the austrian alp. scientists have realised there has an unprecedented glacial melt, so has an unprecedented glacial melt, so the question now is how serious is that melts and what can they do to stop it? welcome to weather world and a view you will never forget. the skyscraper that stands above everything else in london. from up here you can see the haze that stretches over this urban landscape and tells you that the areas different compared to win the countryside. and it is the unique properties of urban air which produces weather and climate

differences which in packed everyone who lives and works in a city. it's called the urban heat island effect. that is built up or man—made area that significantly warmer than the surrounding countryside for not it is often most noticeable overnight when the temperature difference can be as much as 12 celsius between the inner city and the rural surroundings. there are several causes of the urban heat island effect. firstly, dark surfaces and the types of materials used in cities, like concrete and tarmac, tends to absorb more solar radiation on the day and heat up quicker than the countryside. this heat is then released into the city air, creating the warming effect. with high levels of pollutants in the cities, that air is more capable of holding onto the heat, whereas in the countryside where the air is often clearer more of that he can pass through the atmosphere. there's also a lack of evaporation in cities due to less vegetation and fewer bodies water.

in more rural areas this evaporation from trees and water removes heat from trees and water removes heat from the surrounding area. as well as the materials used in cities, the other major contributing factor is the topography of the structure of urban areas. imagine for instance wind flowing in a relatively straight line across open countryside will stop when that blows across an urban area, the buildings create more friction to the flow, aching it slow and more to be learned. this in turn reduces its capacity to disperse heat. so with more than half the world's population living in urban areas, this heat island effect has a huge impact on our weather and daily lives. we are swapping one high—rise for another, as we cross the city from south to north, joining a team of investigating urban weather. what they are discovering could one—day narrow down weather forecast from hold to parts of the city and perhaps even individuals reads. behind me you can see the shard on the london skyline and it is part of

the london skyline and it is part of the research project here where various pieces of meteorological equipment are taking readings of different elements of the weather. one of those pieces of equipment is inside the silver box and that's a thermal imaging infrared camera. this camera is looking down at the city and is taking measurements of temperature coming of different materials, like buildings, roads and vegetation. to tell us more about this camera and what is its measuring the going to meet a ph.d. is due to end. talk me through this camera. “— is due to end. talk me through this camera. —— student. is due to end. talk me through this camera. -- student. what is enjoying us? this infrared camera is sensitive to radiation which can be used to determine surface temperatures. if i was to point the camera at different surfaces, like my hand, surfaces of different to bridge will appear a different colour? yes, this is a thermal graph of the temperatures which you can see through the camera. your hand is appearing cooler than the surroundings. the different colours

represent different temperatures. have a look at how this works down the city. you've got several of these infrared cameras positioned at different places around the building. this one here is looking down at some buildings and roads and vegetation down below us. talk as through what it looks like and what we are seeing on the infrared image. this is a time lapse of imagery. you can see the same principle as with your hand, different colours representing different temperatures. there's variety of colours, meaning the surface and temperatures are highly variable. why are we interested in these measurements? typically we use a satellite base of measurements, looking straight down at the surface. that means they have at the surface. that means they have a preferential view of the roof and ground surfaces as opposed to all surfaces. i'm doing a ground proving exercise here, with lots of measurement of different angles. these temperatures are really

important for evaluation and input. we will have more from the rooftop later. when the going gets hot, you do what you can to stay cool. it's been a summer you can to stay cool. it's been a summer of you can to stay cool. it's been a summer of extreme you can to stay cool. it's been a summer of extreme heat in southern europe. temperatures soaring well into the 40s celsius from spain, across to the balkans. in italy, the heat exacerbated drowned. the pope ordered the famous fountains of the vatican to be turned off to show solidarity with the people of italy and rome, where temperatures hit 43 celsius. hot, dry and now on fire. wildfires led to thousands being evacuated from campsite here in france, in july, spending the night on beaches as the smoke billowed above them. portugal, in june. as the smoke billowed above them. portugal, injune. the catastrophic forest fire kills more than 60 people. the country's worst disaster

for more than 25 years. the majority of people were killed on this road, rapidly engulfed by fire as families already fleeing from their home is where trying to drive to safety. more fire, but a different continent. this is south africa, near cape town, injune, as the drought combined with strong winds spread wildfire sparked by lightning. they followed a major storm that inundated the coastline here, with high seas and big waves. the south african weather service said was the worst winter storm here in 30 years. big storms have hit europe too. this is moscow, in may. a severe thunderstorm, the worst in a century, killed 16 people, toppling trees, with winds of up to 70 mph. and astonishing scenes from poland, in august, as storms bring down tens of thousands of trees,

killing six people. it was declared the worst disaster of polish and possibly european forest history. storms brought devastating downpours. turkey, istanbul, in july. roads turn to readers. there have been a number of flooding storms in the city this dud summer. in the uk storms followed a hot start. this was cornwall injuly. the torrential rain and hail lasted over an hour, causing a flash flood to sweep through the village, taking everything it could carry towards the sea. this woman found her elderly mother's walking frame amongst the piles of debris and next to it even her kitchen sink. it's happened. you can't put it back. you just have to get on and carry on and do what we can. we'll get back to normal. we're cornish! earlier in the summer heatwave provoke an unusual protest at a devon school. boys were told they couldn't wear

shorts, because it wasn't official uniform. so they wore a skirt instead. they can't stop us doing it. girls are allowed to wear skirts. they get cold legs and we have to sit there sweating! the school says as hot weather becomes more common, it may consider a change. protest is real! we are back at our urban experiment on the rooftop in london. earlier, we saw thermal imaging to look at how different surfaces, grass, concrete, humans, heatand how different surfaces, grass, concrete, humans, heat and release the heat at different levels. that's enough of that. that's really important because those different surfaces are also heating the air above them at different levels. different writing of that air. that goes on to affect the air around us and also the weather. ben crawford is monitoring how much the air moving around —— how much the air is

moving around —— how much the air is moving around —— how much the air is moving around us. this measures wind speeds in three dimensions. with this piece of equipment we can measure the cumulative effect of all the different surfaces and their heating of the air. importantly, i'm filling the air blow right at me sideways, but when you are talking about different surfaces heating the airabove, about different surfaces heating the air above, it's rising from ground upwards, which is also measured with this. you would expect that air to be writing differently, depending on where it's come from. exactly. you can imaginea where it's come from. exactly. you can imagine a natural environment like a field or forest and replace that with the city, with glass and concrete and brick, you will change the thermal properties of that and change how the air flows and moves. this is measuring what's going on just here, but you've also got another piece of kit, measuring over another piece of kit, measuring over a big distance? this measures disturbances from the air, from the heat rising, the military shimmers coming offa heat rising, the military shimmers coming off a hot roof or it piece of

concrete. this is pointed across the city towards the foot tower, about four kilometres away. so this really is the invisible world of what's going on in the air right above the cityscape? that's right. with the data from this instrument we can make the invisible visible. here we have a series of days in the summertime in london and we can see during the mid— day, the hottest pa rt during the mid— day, the hottest part of the day, we have the greatest heat emissions and we can see this rise in the graph. overnight when the surfaces cool we can see less heat emission coming off the surface. what does it matter? how does knowing about all of this turbulent air possibly improve the weather forecast for the city? that's a good question. it emissions and turbulence affects a lot of things. it affects air cabbage, wind speed, it affects the dispersal of pollutants and can even impact things like clowns. —— air temperatures. we can narrow down the forecast to a smaller part of the

city? that's right. we can give a specific forecast for a city, and even perhaps later different neighbourhoods in the city. thanks for revealing the hidden world on what's going on in the air around us. what's going on in the air around us. you're very welcome. turbulence and updraughts when airborne our watch hotair balloons try to avoid. but getting airborne is the problem here. we are trying to get airapp. is the problem here. we are trying to get air app. two balloons collide injune. to get air app. two balloons collide in june. swirling winds to get air app. two balloons collide injune. swirling winds blow them off course. luckily what could have endedin off course. luckily what could have ended in tragedy only left one man with minor injuries. lightning sparks across the south wales guy in may. the earth's surface is struck about 100 times every second and were never lightning strikes you can be sure bbc weather watchers will try to succeed where many of us fail to get a good photo of it. this will all taken when storms swept through the

uk injuly. become a bbc weather watchers by signing up online. coming up, how a blanket could help produce a phenomenon known as glacial melt. so faron glacial melt. so far on weather world we've been getting very high—tech at this open weather experiment on this windy rooftop in london. but along with the high—tech, i found rooftop in london. but along with the high—tech, ifound something that's a little bit more familiar, at least to me, which is a weather station. we've seen a lot of these on our travels on weather world. in northumberland we saw a fully working weather station there. insight here we've got a thermometer and it is measuring humidity with this gauge. all inside a very clever box which takes it from the direct sunshine and excessive wind. of course that weather station had a screen kind which it had a thermometer. although this isn't the same as that, it similarly protects that the monitor so we can measure the temperature of the air, rather

than the sun. and we've also got an anemometer. we've been to the birthplace of these on our travels on weather world, the northern —— northern ireland. it all started here. a simple design. the four cups that spin in the wind and you can measure the wind speed. this anemometer is getting a good workout today, but it's really good to know that wherever we go on weather world we can find a weather station. but we can find a weather station. but we will get a little bit more high—tech again later in the programme when we come back year. a time in south—east england. —— but becoming. engenhao dash—cam technology can now do as engenhao dash—cam technology can now doasa engenhao dash—cam technology can now do as a driver's eye view of what it is like to negotiate a flooded road. but things are about to get much worse. “— but things are about to get much worse. —— in—car dash—cam. china and july, and a flash flood after many

days of rain leaves many needing rescue. here, and the injuries, in june, a desperate search for survivors as heavy rain triggers a landslide that kills more than 100 people. from sri lanka to nepal, millions are affected. in nepal, the float is worst in august. alison is used to rescue people trapped in water. in june, used to rescue people trapped in water. injune, torrential rain in taiwan. —— elephants use. more 100 600 millimetres in six hours. similar scenes in japan 600 millimetres in six hours. similar scenes injapan in 600 millimetres in six hours. similar scenes in japan in july, where rain causes more than half a million people out of their homes. when a flash flood russia is a major city, disaster strikes. freetown, when a flash flood russia is a major city, disasterstrikes. freetown, in august. and a massive downpour

causes muddy water to certain industries. then a mountainside colla pses, industries. then a mountainside collapses, bearing whole communities and families as they slept. hundreds are under this flood, and the death toll may never be known. it is the rainy season here, but this year it has come with unusual and deadly ferocity. and just how quickly can rain transform a trader rusty weather —— transform a rusty river bed into it a river? a happy surprise to some of the southern hemisphere for winter, as santiago is hit with snowfall injuly. the snowfall caused treacherous driving conditions, not that these motorists

seem conditions, not that these motorists seem to care. but unusual cold stats look like local anomalies against a tide of record warned. alaska. parts of this us state had its warmest july on record. a council meeting he assigned an agreement accepting the need to tackle climate change. but less tha n need to tackle climate change. but less than a month later, this. in order to fulfil my solemn duty to protect america and its citizens, the united states will withdraw from the united states will withdraw from the paris climate accord. donald trump's announcement brought international condemnation. the world meteorological association said that in the worst case, it could add 0.3 degrees celsius to be covered by 2020 three. —— 2022. i'm

at the top of this glazer in the austrian alips at about 3,000m high. it is an area very popular for skiing. actually, there are about 80 separate glaciers in this area. —— glacier in the austrian alps. this woman is a world renowned glaciologist. she has come up with a surprising answer to our stock, a blanket. on a very small, local scale, we could prevent some very

tiny areas. —— protect. but only about 1% of glazier area can be preserved with this method, and of course, it is very cost intensive and needs much labour. —— glacier. to save 1% of a glacier seems futile. but officials say it is worth it. there are 5000 alpine glaciers in the world. experts say that half will be gone within only a few years, and those that are left will be much smaller. but it is clear this inexpensive local solution can help on a global scale. here on the ice sheet, the problem is super—size. there are fears that the melting is happening faster than expected. this is in part due to allergy on the service of the ice. darker than the ices, it absorbs

more of the son of a warmth. —— algae. bevvy as saying that is going to melt in the next decade, next 100, or even 1000 years. —— nobody is saying. but it does not need to be completely melted for people to be completely melted for people to be in danger. only a small portion is required to raise sea levels, and that threatens coastal communities around the world. and the expansion of renewal, renewable energy is a huge development. —— expression of renewable energy. this is the world's first floating wind farm. so, you have look down towards the ground, and we have seen equipment measured the weather at this level. but now we look into the skies. to do that, i enjoy by natalie. talk us through this piece of equipment,. this is a laser that takes a

snapshot of the atmosphere. you can't see the laser. it measures outside the vehicle spectrum. so this looks 7000, viz in the sky. what is it measuring? it is measuring reflector from what is it measuring? it is measuring reflectorfrom particles in the atmosphere. this could be clad droplets or pollution. —— cloud droplets. so you can get a picture of the clouds and have a picture of how things are at any moment. so now we will talk about the data and how we will talk about the data and how we use it. sue is an urban climatologist with the university of redding. —— university of reading. how is the information useful to

you? is helping us with our weather forecast. but we can also see where clouds form. what we are looking at now is the green is the rural area, and the greater city. you can see the clouds are forming, and what happens to them over cities, and how thatis happens to them over cities, and how that is different. we can compare the difference in the real city with what we can see in forecasts like this. so with all the research going on here, had us that tie together, and what are you hoping to achieve in the future? as we think about forecasting into the future, what we are expecting is that models will allow us to look at things in much more detail, so we can look at, for example, the differences between the northern part of the city and the southern part of the city. hopefully this will make it better for citizens within the city and living in different neighbours. wonderful. so we're looking at more accurate urban forecasting the future. they you forjoining us, sue, and to all your team, too. sometimes you need

to look of your shoulder to see what the weather is doing. this photo of a man unwilling to abandon me his lawn in canada injune took certain media by storm. apparently, the tornado was further away than it looked. we offers see pictures of the northern lines, but these are the northern lines, but these are the southern hemisphere equivalent. it put on a spectacular show in the skies above australia and new zealand in may. and finally, the weather can make us all a little hot and bothered in times. apparently the same goes for gorillas. —— at times. zola creating a splash at dallas zoo. and that is it for this time on weather world. we will be back later in the year. until then, keep checking the forecast. hello.

i'll get to the uk weekend forecast in just a moment, but first of all, what a night in texas. dealing with a major hurricane. this is it on the satellite picture, here. it is a hurricane going to hang around for several more days to come, which means the rain willjust keep on coming. this is how it looks during saturday, bright colour showing the intensity of our rain. but sunday into monday, as well, it's still close by. we're talking hundreds of millimetres here. catastrophic, life—threatening flooding could well be taking place

over the next few days in texas. we'll keep you updated. onto our weekend weather, and some warm, sunny spells on the way for many of us. the chance for catching a shower. but for saturday and sunday, even though there is some around, for most of us it will not. sun for england to begin with on saturday. some showers one or two even in northern england. most places will avoid those and stay dry. if you do get shower in scotland, it could be on the heavy side, maybe with a rumble of thunder. pleasant when the sun makes an appearance, and some spots with temperatures into the mid—20s. the cricket at headingley, as it continues for the next few days, things will warm up. it is a mainly dry pitch. broken cloud and sunshine, turning breezy by the time we get to monday. as to the women's rugby world cup far north in belfast on saturday evening, some cloud around, but is likely dry, and temperatures will ease away after

the warmth of the day. this is a picture through saturday night. dry for most of us. mist and fog developing after a clearer night on saturday night in sunday morning. temperatures for some of us will be a little bit lower. a fine start to sunday. a bit more breeze in scotland, some patchy light rain to be had, here. but the vast majority will be dry. i don't expect necessarily expect clear blue sky. eastern scotland, temperatures will get to 20 celsius, but the higher temperatures will be in england and wales, low to mid—20s. that will continue on monday. ahead of the weather system, more outbreaks of rain in scotland and northern ireland on monday. if it is a bank holiday where you are, there are big contrasts across the uk on monday. so you see the rain moving across scotland in northern ireland,

but that sunshine for many across england and wales. and quite a range of temperatures, too. it will be on the cool side in the wind in scotland and northern ireland, but becoming very warm for a time in south—east england. hello, this is bbc news, i'm gavin grey. these are our top stories. thousands forced to evacuate as hurricane harvey heads towards texas — the category 4 storm could be the biggest to hit the us in more than a decade. not only are we going to be dealing with the high winds that typically come with what should be category 3 hurricane, we are going to be dealing with immense really record setting

flooding. protests turn deadly in india, after a self—styled spiritual guru is convicted of rape — curfews are in place across several northern states. the un condemns the saudi—led coalition for failing to avoid civilian deaths in yemen — at least 1a people are killed in in the latest airstrike. in the latest airstrike. the white house imposes tough new sanctions on venezuela —