Humberto is the first hurricane in a quiet season so far

11 09 2013

The Atlantic hurricane season is usually reaching its peak during the first half of September, but so far the season has been very quiet.

Humberto has just become the first hurricane of the Atlantic season. In the last 70 years only one season has seen the first hurricane form later.

humberto_20130911_1000z

There are various ways of measuring tropical storm activity including the number of storms, the number of hurricanes and something called the Accumulated Cyclone Energy (ACE) Index. The latter measure takes into account both the strength and duration of storms and so gives a good indication of how active a season it has been. Whilst there have been eight tropical storms in the Atlantic so far, many have been weak and short-lived and thus the ACE Index is only running at 27% of where it would be in an average season at this time in the year.

It is not only the Atlantic which is seeing low levels of tropical storm activity. ACE Index across the whole northern hemisphere is running at 42% of average for this point in the season. There have only been two major typhoons in the west Pacific, which is an unusually low number.

It is worth noting that a quiet start to the Atlantic season does not necessarily mean the season will remain quiet. For example, in 2001 there had only been five tropical storms to this point in the season with just one becoming a hurricane. However, the remainder of the season saw another 10 tropical storms of which eight became hurricanes.

Official forecasts of current Atlantic tropical storms are provided by the National Hurricane Center. Visit our tropical cyclone pages for more information or follow @metofficestorms on Twitter.





Media coverage on ‘wet summers for a decade’

19 06 2013

There has been a lot of media coverage today following a science workshop held at the Met Office HQ in Exeter yesterday.

Most of the articles go some way to capturing the science as it was delivered in the press briefing following the event – such as this article on the BBC News website. However, some stories, and particularly some headlines, do not.

The key point revolves around discussion of Atlantic ocean cycles, specifically one known as the Atlantic Multidecadal Oscillation (AMO), which can have an influence on UK summer weather.

Professor Stephen Belcher, Head of the Met Office Hadley Centre, and Dr James Screen, a NERC Research Fellow at the University of Exeter, were careful in their messaging about the AMO.

They talked about initial research which suggests this cycle, which can last for 10-20 years, can ‘load the dice’ to mean we may see a higher frequency of wetter than average summers before switching to its opposite phase, where we may see the opposite effect.

Currently, they said, it appears we are well into the ‘wet’ phase of this cycle, so it may continue to have an influence for a few more years to come.

That does not mean every summer will be a ‘washout’ for the next decade and shouldn’t be taken as a deterministic forecast for what we will see in the years to come.

First of all, we’ve seen five summers of higher than average rainfall in the last six years (with 2010 being the exception, which had average levels of rainfall). Even within each of those years we have seen periods of decent weather – so there’s no expectation of total washouts for the whole summer.

Secondly, the research suggests there is a tendency towards a higher frequency of wetter than average summers – so we could still see summers which buck this trend.

And finally, this research is still at an early phase and more work needs to be done to see exactly how this process works and how we can predict its influence on future seasons.

So, much like a blog we recently wrote about this year’s summer, it’s fair to say that you shouldn’t write off summers for the next decade or so.

We expect to be publishing a guest blog from scientists at the University of Reading on the science they presented to the workshop yesterday, so look out for that in the coming days.

You can now see video of the Professor Stephen Belcher speaking at the press conference which followed the science workshop on 18 June on our Youtube channel.





March – a month of weather contrasts

18 03 2013

Winter seems to have hung on for quite some time this year with low temperatures, frost, ice and snow affecting many areas into late March. This isn’t altogether unusual as we are more likely to see snow at Easter than at Christmas. However, March 2012 was very different with plenty of sunshine and temperatures into the low 20s Celsius. How come?

Well, this time last year the UK was under the influence of high pressure. This gave us clear skies, plenty of sunshine and with a light southerly breeze, temperatures that were well above average. In fact, Scotland set an all time record maximum temperature with 22.8 °C at Fyvie Castle in Aberdeenshire.

Visible satellite image from March 2012

Visible satellite image from March 2012

This year, with a strong easterly wind bringing cold air from Scandinavia and Eastern Europe, we have quite the opposite with eastern parts of the UK in particular seeing snow, ice and temperatures around 20 degrees Celsius lower.

Visibile satellite image from March 2013

Visibile satellite image from March 2013

The direction of the wind therefore plays a major part in what type of weather you and I will see, especially as we have the Atlantic Ocean to our west and continental Europe to our south and east. Different wind directions bring air with different temperature and moisture contents. Meteorologically, they are termed air masses and in March 2012 we saw a Tropical Continental air mass bringing dry and warm air from the Mediterranean. This year we have been affected by a Polar Continental air mass, bringing cold air from the east. The following video explains exactly what we mean by air masses.

With different air masses constantly affecting the UK, the weather is a particularly challenging thing to forecast, especially so in March. This is because in early spring the sun is starting to rise higher in the sky and the amount of daylight hours start to increase. This means we get more heat building up in the lower part of our atmosphere. The result is slightly more energy, which in turn can lead to heavier showers. We can also see more unstable air and more active fronts as a result of greater heating. With more moisture available in the atmosphere, we also tend to see heavier or more prolonged rainfall and if this mixes with cold air, more snowfall. It makes forecasting more complicated because the extra heat and moisture adds another aspect to the weather, which tends amplify the effects of different air masses.

You can find out more about forecasting snow on our website or on the following video:





2012 hurricane season comes to an end

14 12 2012

This year saw another active season in the North Atlantic with 19 named storms, of which 10 became hurricanes.

Both the number of named storms and hurricanes were well above the 1980–2010 averages of 12 and six respectively. However, only one of these (Michael) became a major hurricane, which is below the average of three.

Unusual season

It has been an unusual season in many respects. This is the third year in a row with 19 named storms, which is unprecedented in the historical records. Only one other season – 2005, which saw the devastating Hurricane Katrina – has experienced more named storms (28) since reliable records began in 1944.

The season has also been notable for the high number of relatively short-lived storms, with seven of the nine tropical storms lasting just two days or less. These storms contribute towards a high storm count, but relatively little towards the Accumulated Cyclone Energy (ACE) index – a measure of the combined strength and duration of all named storms in the season.

Joanne Camp, a long-range hurricane forecaster at the Met Office, explained that having so many short-lived and relatively weak tropical storms was a notable feature of the season: “If you look at the long-term record, this is unusual – but it has been an increasing trend over recent years.

“It is almost certainly due to the improvement of technology, such as satellites, which allows us to observe developments over the North Atlantic in ever greater detail. This means that we are now identifying storms that could previously have gone undetected.”

Many storms – but not much power

Because such a high proportion of this season’s storms were short-lived and weak, the ACE index was only moderately above average at 127. The average is 104. Many seasons in the historical record have had a much lower total tropical storm count, but much higher ACE index,  for example the 2004 season recorded only 14 named storms but an ACE index of 225 – nearly twice  that seen in 2012.

The Met Office public forecast for the North Atlantic hurricane season, which is issued in May, continued its run of providing good guidance on the ACE index – with this year’s actual total well within the predicted range. On the number of storms, the total of 19 this year is outside of the forecast range.

Chris Landsea, Science and Operations Officer at the National Hurricane Center in Miami, said: “Because we are now better able identify weak, short-lived tropical storms than we were just 15 to 20 years ago, a simple count of how many storms occur in a season is perhaps not the most representative measure of how active a season has been. Using ACE index or number of hurricanes would be a more stable measure, less prone to changes in technology during the last 40-50 years.”

Experimental forecasts run by the Met Office during the 2012 season show that there is skill for forecasting the number of hurricanes. In May 2012 the Met Office predicted that the most likely number of hurricanes to occur during June to November 2012 would be six, with a 70% chance that the number would be in the range two to ten. In the event ten hurricanes occurred.

Significant storms

The most notable storm of the 2012 season was Hurricane Sandy (also referred to as Superstorm Sandy), which became one of the largest storms on record, measuring over 1000 miles across. The storm resulted in 253 deaths (at least 122 of those in the Caribbean) and is estimated to have caused over $65 billion in damage – making it the second most costly hurricane in US history, behind Hurricane Katrina.

GOES-13 natural-color image of Hurricane Sandy at 17:45 UTC on October 28, 2012.  CREDIT: NOAA/NASA GOES Project.

GOES-13 natural-color image of Hurricane Sandy at 17:45 UTC on October 28, 2012. CREDIT: NOAA/NASA GOES Project.

The Caribbean also experienced a number of tropical storms during 2012 season. Hurricane Isaac caused severe damage in Haiti and eastern Cuba before making landfall along the northern Gulf Coast of the USA. Tropical Storm Rafael passed close to Puerto Rico and the British Virgin Islands. Hurricane Sandy made landfall over Jamaica and Cuba before heading to the northeast coast of the USA and Hurricane Ernesto made landfall over Central America.

No major hurricanes (those registering category 3-5 on the Saffir-Simpson hurricane wind scale) have made landfall in the US since Wilma in 2005 – a near-record length of time.

Longer-term trends

Overall the relatively high level of Atlantic hurricane activity continues a trend which started in 1995, with most years since then being above-average. To assess long-term cycles in North Atlantic hurricane activity the Met Office is trialling experimental forecasts for up to five years ahead.

While this research continues, the Met Office’s hurricane experts will continue to monitor the drivers of tropical storm activity over the next few months as they prepare the first forecast for next year’s season, which will be issued in March 2013. The main public forecast will be released in May 2013.

Further details on the 2012 season can be found in this year’s verification report (PDF, 1 MB).

For regular updates on tropical cyclones worldwide follow @metofficestorms on Twitter.





Hurricane Sandy threatens severe weather for US East Coast

26 10 2012

Over the last two days Hurricane Sandy has cut a swathe through the Caribbean bringing strong winds, heavy rain and storm surge to Jamaica, Cuba, Haiti and the Bahamas. At least 20 people have been killed, properties damaged and flooded and at one point large parts of Jamaica were without power.

Hurricane Sandy is now moving away from the Bahamas, but is still very close to the south-east coast of the USA. The east coast of Florida is experiencing stormy conditions as Sandy moves northwards over the Atlantic Ocean.

Hurricane Sandy 26 October 2012

Sandy looks likely to turn north-west early next week and impact parts of the mid-Atlantic and north-eastern USA as did last year’s ‘Halloween Nor’easter’ storm of 2011 and the ‘Perfect Storm’ of 1991. As Sandy approaches land the warm moist air circulating within the hurricane looks sets to meet cold air spreading south into the north-eastern USA from Canada. This provides the potential for the storm to develop further and produce severe winds, heavy rain, flooding and even snow on its north and west flanks as it hits land.

Uncertainties remain as to the precise location and timing of landfall. However, the area most likely to be affected stretches from the states of Maryland to Massachusetts, including the populous cities of Washington DC, Baltimore, Philadelphia, New York and Boston.

Official National Hurricane Center Forecast for Sandy on Friday 26 October

The National Hurricane Center (NHC) and the US Federal Emergency Management Agency (FEMA) are providing warnings and advice to those who are potentially at risk from the storm. The Met Office routinely supplies predictions of hurricane tracks from its global forecast model to NHC which it uses along with guidance from other models in the production of its forecasts and guidance.

You can keep up to date with tropical cyclones around the world on our website or follow us on Twitter.





What’s bringing the stormy weather to the UK?

24 09 2012

The UK has seen some very wet and windy weather since the early hours of Sunday morning and that is set to continue in places for the next couple of days – but what has brought these disruptive conditions?

As is the norm, a low pressure which moved in from the Atlantic is to blame, bringing bands of heavy rain and strong winds (as you can see from the tightly packed isobars on the image below).

Forecast synoptic chart for 12:00 on Tuesday 25 September showing the low pressure over the UK.

Despite some reports to the contrary, this low is not what’s left of tropical storm Nadine, but is a completely separate entity – the remnants of Nadine are currently sitting close to the Azores far to the south of the UK.

Some warm tropical air dragged over by Nadine was sucked up into the low pressure, however, giving it some extra energy – essentially increasing its potential for strong winds and rain.

This isn’t unusual though, virtually every weather system we see will have had some input of sub-tropical air during its evolution.

There are two more notable features of this low pressure, however. Firstly, it has remained unusually active as it sits over the UK, leading to the strong winds and heavy rain.

This is due to the fact that, as the low pressure system moved north across the UK, it has also pulled in cooler polar air from the north.  This cold air has come up against the warm sub-tropical air, re-invigorating the depression and allowing it to continue to deepen over the UK.

Secondly this low pressure is lingering for longer than we would often see. The reason for this is down to the position of the jet stream, a narrow band of fast moving winds high up in the atmosphere which ‘steers’ weather systems.

Normally the jet stream runs fairly directly from east to west and pushes weather systems through quite quickly. Similar to earlier this year, the steering flow of the jet stream is currently in a meandering mood – looking much like a river, curving north and south as it heads west across the Atlantic (we call this a meridional flow, with the more linear west to east flow being called a zonal flow).

When it meanders, weather systems can get stuck in the ‘peaks and troughs’ it creates – so they get stalled in one spot rather than moving on. The below picture of the jet stream as at 12:00 today shows with the steering flow of the jet over France and the UK in the resulting trough.

The weather system will move on during the day on Wednesday, but that still means the UK will have had three days of unsettled weather.

Like our weather, the jet stream can change rapidly and it’s difficult to forecast precisely what it will do for more than a few days ahead – so there’s no reason to expect it to continue to behave in this way and there’s plenty still to play for in terms of our autumn weather.

The low pressure system that is affecting the UK is unusually deep for September, with the lowest air pressure recorded so far being 973mbs. To find a similarly intense low pressure system in September you need to go back to 1981, when pressures below 970mb were reported over a period of 24 hours. Like this week’s, this low pressure system brought unsettled weather as it crossed the British Isles – starting in the Isle of Man and tracking east and then north to cover Cumbria, Northumberland, eastern Scotland, Orkney and Shetland. There have been other times when pressures as low as 970mb were recorded in some parts of the British Isles in September, such as in the Isles of Scilly in 1995 and others across the far north or west of Scotland or Northern Ireland, however none were as widespread as the low that pushed across the UK in 1981.





Further hurricanes expected in west Atlantic

9 09 2012

The Met Office has been closely monitoring Tropical Storm Leslie during the past week, especially because of the possibility of the impact on Bermuda. It now looks like Leslie will strengthen to Hurricane Force as it tracks 100-150 miles east of Bermuda late on Sunday. Therefore, although around 100 mm of rain and gale force winds are expected, no significant impact is expected across Bermuda, although dangerous rip currents are predicted by the US National Hurricane Centre.

This graphic shows the position and forecats track tropical storm Leslie. The orange circle indicates the current position of the center of the tropical cyclone. The black line and dots show the National Hurricane Center (NHC) forecast track of the center at the times indicated. The dot indicating the forecast center location will be black if the cyclone is forecast to be tropical and will be white with a black outline if the cyclone is forecast to be extratropical. If only an L is displayed, then the system is forecast to be a remnant low.

This graphic shows the position and forecast track tropical storm Leslie. The orange circle indicates the current position of the center of the tropical cyclone. The black line and dots show the National Hurricane Center (NHC) forecast track of the center at the times indicated. The dot indicating the forecast center location will be black if the cyclone is forecast to be tropical and will be white with a black outline if the cyclone is forecast to be extratropical.

All available forecasts track Hurricane Leslie, and Hurricane Michael, which is situated to the east, quickly north through Monday and Tuesday.

Meanwhile, an active cold front which was responsible for the rare New York tornadoes and the high profile disruption to the US Tennis Open Championships will continue to move east from the eastern seaboard of North America.

Hurricanes Leslie and Michael and this cold front are expected to converge east of Nova Scotia and south of Newfoundland bringing the risk of 100-200 mm of rainfall to the area through Monday and Tuesday.

Probabilities of surface wind speeds exceeding 58 mph

Probabilities of surface wind speeds exceeding 58 mph from US National Hurricane Centre

However the main risk remains to the marine community with wind speeds in excess of 65 knots from late Monday to early Wednesday. Combined with eight metre waves and potentially a maximum wave height of up to 16 metres there will be hazardous sea conditions across the Grand Banks fishing grounds which is the same area as was impacted by the ‘Perfect Storm’ in the Autumn of 1991.

Beyond this, the remnants of this combined storm may swing east and push across the Atlantic, influencing the weather over the north east Atlantic toward the end of the week. Currently the area of low pressure is expected to push well to the north of the UK, but will potentially push a frontal south across the UK bringing rain and gale force winds to the north on Thursday and Friday. However there is still a good deal to play for in the forecast for the end of the week and you should keep up to date with the latest weather forecasts and warnings on the Met Office website.

Pakistan Monsoon brings exceptionally heavy rain.

Elsewhere, the Pakistan Monsoon has brought some exceptionally heavy rain to the region. Khanpur, on or close to the Indus River in Pakistan reported 147mm of rainfall in just 12 hours up to midnight last night UK time. Such heavy and intense rainfall associated with the Indian Monsoon is likely to bring significant and rapid localised flooding issues to this area in the coming days. 

Across Sindh and Punjab provinces over the last 72 hours stations have been reporting varying 12-hourly totals with anything between 10 and 60 mm at times.  

Forecasts indicate that rain is expected to continue for another 48-72 hours, with peak intensity over next one to two days. So the situation could worsen initially before events begin to ease off slowly during the early part of next week.





Met Office in the Media: There is no need for alarmism

12 10 2011

Over the past few weeks some parts of the media have carried some colourful headlines about what’s in store for this year’s winter. Reports of ‘-20 °C within weeks’, ‘a winter fuel crisis on the way’ and ‘widespread snow by the end of October’, have all whipped up a frenzy of expectation for an ‘Arctic winter’.

In response Met Office Chief Executive, John Hirst has written in The Times today calling for a sense of reason in light of these headlines that can confuse and even scare vulnerable people in our society.

You can read the opinion piece here:

Winter will be cold – but don’t panic just yet

 It’s absurd to make alarmist forecasts of a whiteout. That’s not how our weather works

 Last year Britain had the coldest start to winter in 100 years and the repeated snowfalls over 40 days before Christmas cost the economy up to £130 million a day.

So it is understandable that there is intense interest in this year’s winter. But the colourful recent headlines predicting “-20C within weeks”, “a winter fuel crisis” and “widespread snow by the end of October” bear no relation to the kinds of weather that forecasters at the Met Office are currently expecting — there is no need for alarm.

These stories do reflect our national obsession with the weather but they can also confuse and even scare vulnerable people. The Met Office’s job is to provide accurate and reliable information and at this stage we see no scientific evidence to support these premature predictions. In fact the scientific capability does not exist to allow such extremes to be identified on a long-range timescale.

We can say with reasonable certainty that today will be largely overcast, with rain for many places, but as we move towards the weekend it will become mostly dry with skies brightening in the south and east. Over the weekend rain will move southeastwards. We can also say that the current 30 day outlook suggests that next week will be rather cold at times with some snow over high ground in the north of the UK, and frost in some sheltered locations too. What no forecaster can say is whether we’ll see a week of -20C temperatures in Manchester in the second week of December.

This does not mean that harsh winter conditions are not possible, just that they cannot be identified at the moment.

As winter approaches, local government and businesses are preparing for the worst that the British weather can throw at us. But the fact that local authorities are stocking up on grit is no cause for alarm. This is what contingency planners do. In fact, their preparations are encouraging because they mean the country should be in a good position to respond to our short-range forecasts of severe weather.

Last year there was some confusion between our longer-range outlook which provided good advice over the whole winter — as January and February were relatively mild — and our shorter-range forecasts that correctly identified the prolonged cold and snowy weather early in the winter. In fact, our forecasts of where and when it would snow were second to none. Although it is not possible to prevent disruption, our detailed forecasts allowed agencies to put their resources in the right place at the right time to ensure that it was kept to a minimum.

You may ask why we can provide long-term forecasts for things such as the North Atlantic tropical storm season, but doing the same for the UK is still so difficult. It is because the UK is a small island sandwiched between an ocean and a continent, and it lies on a latitude where warm tropical and cold polar air masses fight for supremacy. The UK is also about as far away as it is possible to be from key drivers of long-range predictability, such as La Niña. It’s perhaps no coincidence that the Met Office and the Japanese Meteorological Agency are consistently ranked the top two operational forecasters in the world, given that both ply their trade on island nations with notoriously changeable weather.

There are many contributing influences to long-term weather patterns, such as Atlantic Ocean temperatures, pressure patterns and the extent of Arctic sea ice. Research published by us only this week casts new light on how solar ultraviolet output affects Europe’s winter weather. The long-term challenge is to understand how they might be affected by a changing climate.

In recent years we have seen great scientific and technological advances that allow us to warn of impending severe weather with ever greater lead times and with ever greater detail. Rest assured that this year the Met Office will continue to offer that service, warning of any severe weather in plenty of time to get out the gritters — and the jumpers — when it matters.





Update on Katia as she heads toward the UK as a post-tropical storm

11 09 2011

The forecasting team at the Met Office are continuing to keep an eye on the remains of Hurricane Katia as it moves across the Atlantic Ocean. Katia is now a post-tropical depression lying around 600 miles west-southwest of Ireland with a central pressure of around 966 mbar. The system is expected to continue to move northeastwards across the Atlantic, increasingly affecting northern UK during Monday. Please keep up to date with the latest on our warnings page.

 








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