Im in florida in the United States where the power of Hurricane Irma has had devastating consequences. And well be speaking to scientists about forecasting Tropical Cyclones here in the Weather Centre. Key indicators are the atlantic in august and september. We will be looking at the seasons other major hurricanes, including harvey and maria. Plus the Science Behind these monster storms, and how Climate Change could be affecting them. From harveys unprecedented tropical deluge in texas. And irmas record breaking intensity as it slammed into the caribbean, before heading to florida. To the explosive intensification of maria, as the caribbean took another devastating hit. This is the story of a Hurricane Season that at times has produced more power, more rain, and more destruction than ever recorded. Its one thing to talk about wind speed, and pressure, but its a completely different thing to experience a hurricane first hand. Welcome to this special edition of weather world. From here in florida, where the extensive damage caused by Hurricane Irma will take months to repair. It was here, in september, when Hurricane Irma became part of one of the most destructive Hurricane Seasons, and some say the most damaging since Hurricane Katrina slammed into new orleans, killing 1,800 people over a decade ago. Before Hurricane Irma, there was harvey, as nick explains. Here at the bbc Weather Centre, weve been following the twists and turns of a remarkable and record setting atlantic Hurricane Season. Hurricane harvey, bound for the texas in august, brought warnings of catastrophic flooding. And it went on to become the usas wettest Tropical Cyclone it has recorded. 4,323 days, almost 12 years that is how long it had been since a major hurricane had hit the usa. But harvey changed all that. Dan, are you in here . Having rapidly intensified since it formed in texas, as a category four storm, with winds of 130mph. It was the most powerful hurricane to hit texas since 1961. Did you sleep . No, i secured the roof, and about 10 30pm, there is a tree in my yard. And then their house is completely gone. But, after the initial destruction, worse was to come. Harvey stalled near the texas coast, only slowly edging towards louisiana, still able to tap into the warm sea. It became a prolific rain maker. As streets turn into rivers, the us to prescribe the situation as unprecedented. This was new hurricane territory, and houston, the fourth largest city in the usa, was in the bulls eye. And, as the deluge went on, more and more people had to abandon their homes to the rising floodwater, with anything that could float becoming part of a makeshift armada leading people to safety. This is what harvey did to houston, killing it at least 30 people in this area alone, and more than 80 in total. These pictures show the remarkable transformation to the landscape from harveys rain. As much a 64 inches, over 1,600 millimetres of rain, fell in a week long deluge, causing billions of dollars of damage. Hurricanes a Formidable Force of nature that can cause devastation to all in their paths. So just how do they form, and why has 2017 been so intense . Lets take a look at the Science Behind the storms. Hurricanes form due to an area of low pressure that strengthens rapidly over tropical or subtropical waters. A cluster of thunderstorms can form, and these clusters of thunderstorms then draw in a flow of warm and moist air, as they move over these warm waters, creating a low pressure centre. Now, if conditions are just right, a Tropical Storm is born, which can then strengthen into a full blown hurricane. Now, this year, there has been a particularly strong west african monsoon, meaning bigger and more frequent storms in the Hurricane Development zone. Now, several specific conditions need to come together to trigger hurricane formation. Firstly, temperatures need to be higher than 26 celsius to provide the fuel for these big storms. This year, waters across the western atlantic and the caribbean had often been high for the time of year. And also, we need a lack of wind shear. Now, wind shear, in other words, is when winds that dont very much in speed and direction, but in height. But lower wind shear allows a storm to rise vertically. Also, el nino has been stuck in a neutral phase. That has led to lower wind shear and increased hurricane prospects. The storm has to be a sufficient distance away form the equator for the coriolous effect kicking to provide the spin. Now, all of these conditions have often come together doing this yea rs Hurricane Season, producing several hurricanes of more than six miles high, and hundreds of miles wide. Now, earlier, we had how harvey set new records for rainfall. The next hurricane, irma, was also to take its place in the record books for power and intensity, and tomasz experienced it. Hurricane irma, bearing down on the caribbean in Early September as a maximum category 5 storm, with winds of 185 mph, the strongest hurricane ever recorded this far east in the atlantic. This is what it sounded like as irma moved across the northern islands. And this is what a category 5 hurricane leaves behind. The island of barbuda, from caribbean paradise to ruins. Everybody its just gone. What do you do now . I dont know. Im just waiting to get evacuated from here, and then im going to come back, and try and salvage something, and help, i dont know. My whole life is here, so. But it wasntjust barbuda. Irma caused extensive damage here in the British Virgin islands, plus st martin, st barts, anguilla, and the turks and the caicos islands. After briefly weakening, irma was back to category 5 strength, with winds of 160 mph. As it made landfall in cuba, creeping along the islands northern shore, for most two days. As irma was hitting cuba, i was in the United States, which was waiting for its second major hurricane in as many weeks, and this time the target was florida. Hurricane irma is battering cuba, around 300 miles to the south of us. And, even here, you can feel the power of the storm. Thats how big it is. Irmas florida landfall was in the keys, causing major damage as a category 4 storm, with winds of 130 mph. As irma moved north, this was the scene in naples. The eye wall is coming upon us, its getting really intense now at the centre section. And then irma reached my location, in tampa. It had weakened slightly, but it was still a category 2 storm, and i wanted to see if it was safe to experience the conditions outside. Its one thing to talk about wind speed and pressure, but its a completely different thing to experience a hurricane first hand. It must be devastating for people caught in the storm. More than 120 people are known to have died as a result of irma, including at least 80 in the United States. But, as the clean up began here, it wouldnt be long before the caribbean was in the firing line again. But how do we knowjust how strong these hurricanes like irma are, before they hit land . Here is nick again. Commercial aircraft steer around hurricanes, but not the hurricane hunters, including these of the us air force reserve. Their mission is to fly when no one else dares, this time right into the heart of Hurricane Irma. The more times we pass through the eye wall, the better they can calibrate exacting where the storm is moving. Youre flying through stuff no one else flies through, its not pretty. But all the training you do has to kick in all at once, because the plane is falling and you are just holding on looking for good air. We are back now at the bbc Weather Centre, and im joined by professor mark saunders. Mark is a climate prediction scientist. He is involved in predicting hurricanes and Tropical Cyclones right around the world. So thank you forjoining us. Just expect to me, how do we even begin to predict a Hurricane Season . We use computer models. Between august and september, two of the key environmental fields are how warm or cold the Tropical Atlantic sea temperatures are in august and september, and how strong the trade winds are, blowing across the atlantic from west africa to the caribbean. And, if we can pick those perfectly, then you can generally get a very good understanding of how active or quiet the Hurricane Season will be. 2017 has been a particular Hurricane Season. Did the forecasters get it right, and if not, what went wrong . We got it right to a large degree, in that most forecasts predicted it would be above normal Hurricane Season. But not the actual hyperactive levels, they were not anticipated. We think one of the factors that contributed that mis forecast was the sudden cooling of the waters in the tropical areas called el nino. Waters called by a big degree by august, thats quite unusual and contributed to a more stable atmosphere conditions over the Tropical Atlantic, which enable storms to build up and become stronger, and also have more of them. Thank you forjoining us. And coming up, from the hurricane front line, i will be giving my experiences of reporting joined the storm. And what caribbean caves can tell us about hurricanes of the past and future. So far in this weather World Special weve been concentrating on Hurricane Irma. But it wasnt the only Tropical Cyclone with the deadly impact. It too would reach category 5 strength and head for the caribbean. Nick has the story of hurricane maria. Here we go again, september, and yet another hurricane rapidly intensifies. This is guadeloupe, hit by wind and rain, a months worth injust a day. But, by the time marias eye had passed, dominica had taken a hit. This unverified video was made as the lights went off. After the hurricane, the full horror of what happened here was revealed. These were the strongest winds on record to have hit this island, and at least 30 people were killed. When maria made landfall in puerto rico, it was a category 4 hurricane, and the strongest here since 1920s. As ever, its notjust the winds that does the damage. Its the water, too, both from flooding rain and the storm surge, causing catastrophic flooding. All of the elements combined to leave the entire island without power, amid fears of a high humaintarian crisis. Maria then came close to the dominican republic, before turning north, away from the usa. In october, another storm followed maria. As a Tropical Storm, it first made landfall in nicaragua, with severe flooding damaged thousands of homes. Nate was blamed for the deaths of at least 25 people, including nicaragua, but in costa rica and honduras, too. Next in nates sights was the usa. Strengthening, it became the fastest moving hurricane ever recorded north of mexico. It hit mississippi as a category one storm. But, at least with this hurricane, impact in the usa were not as serious as has been feared. We know a lot about hurricanes in the era of modern weather technology, past 100 years or so. But what about the hurricanes that came before that . Well doctors james and lisa baldini from Durham University running a project in the caribbean to answer that question. Thanks forjoining me. It involves being to caves. Yes, it does. Caves are the most obvious place to look, but in fact they are full of really interesting deposits called stalagmite and stalagtites. What we aim to do in this project is to reconstruct long term records of hurricane impact, and. Youve got a stalagmite here, what does that tell you. They grow up from the ground of the cave, and they are deposited as the drip water drips onto the ground. That drip water has a chemical signature that reflects the rainfall at the time it was going. Hurricanes have a really unique chemical signature, because the water actually evaporates from the ocean surface, and it is drawn up kilometres in the sky, and that is where temperatures are lower, and it impacts the chemical signature of that rainfall, so we can look at the chemistry, going through a time, and we can pick out years when there were more hurricanes, and years when there were fewer hurricanes. So the information you can learn depends on how old the stalagmites are . Yes thats right. The record we had to about is back to 1550a. D. At about 450 years long. But stalagmite can grow for a very long amount of time. We can date them 600,000 years ago. It is likely we will be able to extend that record. That will give us the information that we will need to assess what is happening now. I am fascinated to learn what you have learned so far, but the indications for the future, we will look at that, for now, thank you. From science success to an infamous epic fail. Earlier on today, a woman on the bbc had heard that there was a hurricane on the way. If you are watching, dont worry, there isnt. Michael fishs ill fated reassurance of the storm that hit 30 years ago was technically correct. It was not a hurricane, but a area of low pressure that felled 15 million trees. The storms wind gust of 115 mph was recorded in west sussex. Sustained winds that strong would rank as a category three major hurricane, but just how are hurricane wind speed ranked . Heres sarah. We often talk about the strength of hurricanes in terms of their categories. Atlantic hurricanes measured on the Saffir Simpson scale. This is a one to five scale based on wind speeds. The skill provides examples of the type of damage and the impacts associated with given wind speeds. Category one, winds are between 7a and 95 mph, and can cause some damage to roofs and gutters and topple small trees. Category two, winds between 96 to 110 mph. They can cause more extensive of damage and power failures. Category three, storm becomes a major hurricane, with winds between 111 and 129 mph, and can lead to devastating damage to buildings. Category four hurricanes produce winds of 132 to 156 mph, enough to caused catastrophic damage to roofs and exterior walls and power cuts that can last for months. Category five hurricanes, wind speeds in excess of 157 mph. This will cause catastrophic damage to entire homes and buildings too. Affected areas will become uninhabitable. Destructive winds and torrential rain. This looks like a hurricane. In fact, its a typhoon. It was slamming into Chinas Guangdong coast in august. The reason for the similarities that hurricanes and typhoons are the same in everything but name. Earlier on in the programme we looked to do a Fascinating Research project in place in the caribbean. This was true caves through the use of stalagmite. We have not yet revealed what you have found out through the study of what is happening with the stalagmites. What have you discovered . What we see is a peak in Tropical Cyclone activity affecting our site and around 1650ad, around 400 years ago. This is in belize . Yes, this is in belize. We see this peak in activity affecting our site around 1650ad. Now, 1650 was remarkable, because it was the peak of what is known of the little ice age that affected the Northern Hemisphere. After that, the Northern Hemisphere temperatures were warming, but we see a decrease in Tropical Cyclone over time. I think first it is important to emphasise that there is a lot of randomness with how hurricanes go. So any given year 2017 is a good example of this hurricanes can either steer out into the atlantic, or hit central america. There is a lot of randomness about where they go. The average track through time is migrating north. Unfortunately, what this means is that hurricanes can still strike in the atlantic basin, but on average, the north east coast in north america can expect in increase in the number of hurricane landfalls. Thinking along the lines of Hurricane Sandy in 2012. Its could become increasingly normal over the next few decades. Is there something in this that may make people in europe sit up and take notice . We see that the dominant cyclone track is moving northward through time, this also means that there could be an increase in the frequency of storms in the north atlantic, and also potentially impacting europe. Is this an ominous sign for europe, and other major hurricane, but this one further east in the atlantic than ever seen before . Hurricane 0phelia first started wildfires in spain, killing more than 40 people. Then, as it sped north, it remains a powerful storm. Ireland bore the brunt, with three people being killed. Elsewhere in the uk, dust from the sahara carried along by 0phelia, gave the sun and unusual red glow. Hurricanes rightly leads to mass public evacuations, and one of the biggest in American History trip is ahead of irma. Butjust as most is the boar are leaving, but whether reporters butjust as most people are leaving, weather reporters go to the storm, getting as close as they can, to tell the story. This was in florida, but it requires is National Team and technological effort. This is where i was doing this height of the storm in downtown tampa. Hurricane irma holds the record for sustaining category five for longer than any other storm in history. To the viewer, it may have seen that i was anyone there, but there was the cameraman and the producer, out in the middle of the street. I lost everything in my home. What can be destroyed in a matter of hours can take weeks, months and maybe years to repair. Here in puerto rico, just as many have caribbean islands, the damage was extensive, with power, food and water shortages. In the British Virgin islands they were delivering desperately needed aid. Here in the turks and caicos islands, the story is the same. Hurricanes come and go, but the effect that they have on millions of lives goes on long after the storm has passed. And that is it for this special edition of weather world, with nick and sarah in the bbc Weather Centre in london, and from me here, until then, keep checking the weather. Hello there. Storm brian has been bringing strong winds across the United Kingdom over the last 24 hours. The centre of brian moving out into the north sea, were it will weaken through the course of the day. Today, rain or showers showing up on the radar picture. Strong winds around the coastline of wales and south west england, yesterday. The forecast was for gusts up to 70 mph, which was not far off the mark. Inland, forecasts of 40 or 50 miles an hour. Those kinds of values in many inland areas. It was kind of a typical autumnal windy day. Those winds still with us for the early risers for the first part of the morning. Outbreaks of red across western scotland, north west midlands, north wales. The gusts around 40 to 50 miles an hour in the pennines and on the irish sea coast. Maybe one or two slowly stronger gusts. Temperatures 9 11 degrees first thing. There is brian, working to the north sea, where it there is brian, working to the north sea, where it will continue to weaken and die on sunday. What follows through sunday afternoon will be a mixture of sunshine and showers. The majority of the showers and Western Areas of the uk. Dry weather across the east. North westerly winds bringing call and fresher air. Dry weather across the east. North westerly winds bringing call and fresher air. Temperatures a bit down on those of yesterday. Highs between 11 and 14 degrees. Through sunday night, the next weather systems coming through bringing some rain. Averages rising in the south west. 12 degrees as a low down towards south west england. Cooler conditions for a time across scotland a north east england. Monday, this strip of rain will continue to push a lot of cloud and outbreaks for rent for many. Heavy rain for northern scotland at some times. The sky is working to Northern Ireland and scotland as we go through monday afternoon. It gets milder, with temperatures of 70 degrees across some areas monday afternoon. That is a sign of things to come. On tuesday, this trailing weather front comes through the south west. Rain for many of us, but the best in the sunshine really for eastern scotland and parts of north east england. Notice the temperatures continue to rise. Temperatures for many of us between 14 18 degrees. A sign of things to come. Because thursday, mild weather for this time of year. Highs of 22 degrees. Pretty unusual for them this time in october. And that is your weather. This is bbc world news. Im gavin grey. Our top stories catalonias leader says he will not accept madrids plan to curb the regions powers. Thousands take to the streets of barcelona as Carles Puigdemont makes a passionate appeal for the defence of catalonias rights. We do what we do because we believe in a democratic and peaceful europe. After growing international criticism, the world health 0rganisation says its rethinking a decision to make Zimbabwes President a goodwill ambassador. Millions of people across japan are voting in a snap general election well have the very latest live from tokyo. The polling stations opened a couple of hours ago