What’s been happening to our weather?

31 12 2015

December 2015 will go down in meteorological history as one of the wettest – and warmest – on record. It will also be remembered for the devastating floods in Cumbria, Lancashire, Yorkshire and Scotland. The extensive flooding of homes and businesses, loss of electrical power, major damage to roads and bridges, and disruption to the rail network have caused great misery and incurred huge losses.

In this blog our Chief Scientist, Professor Dame Julia Slingo, discusses what factors may have influenced the record breaking weather we have seen in recent weeks.

As with all high-impact weather, the meteorological set-up was critical in defining the severity of these events. Throughout the month, the winds have come from the south or southwest, bringing both extreme warmth but also very high levels of moisture.

There has been a lot of debate whether this has been associated with El Nino – an intermittent warming of the equatorial Pacific Ocean which has been very strong this year – or whether this is a sign of a changing climate. The links to El Nino are certainly very clear in the set up of large waves (troughs and ridges) in the atmospheric circulation, which we expect to see in these events.

Latest monthly anomalies in sea surface temperatures showing the strong El Nino lying along the equator, the warmth of the north-east Pacific and western Atlantic and the colder than normal ocean temperatures of the northern North Atlantic

Latest monthly anomalies in sea surface temperatures showing the strong El Nino lying along the equator, the warmth of the north-east Pacific and western Atlantic and the colder than normal ocean temperatures of the northern North Atlantic

However, it does seem that this year the unusual warmth of the North East Pacific Ocean may have altered the position of these waves across North America and into the Atlantic sector, setting up the conditions for the devastating tornadoes in the US and for the southerly feed of moisture-laden air into the UK.

Circulation anomalies in the middle troposphere for 1-30 and 24-30 December

Circulation anomalies in the middle troposphere for 1-30 and 24-30 December, showing a persistent pattern of troughs (blue/purple) and ridges (green/orange) across the US, North Atlantic and into Europe. The trough over the western US set up the conditions for tornadoes along the confluence of cold air from the north with very warm air from the Gulf (see elevated sea temperatures above). The southerly airstream from Spain to the North Pole is established by the gradient between the trough over the North Atlantic and the ridge over Europe.

Storm Desmond in early December was associated with a strong west-south-westerly flow around the ridge over the eastern seaboard of the US, reaching far back across the Atlantic, as far as the Caribbean. With ocean temperatures well above normal in the southern part of the North Atlantic (see above) – possibly due to the much weaker than normal hurricane season this year associated with the current El Nino – the air was primed with more moisture than normal. This river of atmospheric moisture fed the storms that formed on a stronger than normal jet stream, and as the air impinged on the mountains of Cumbria, large quantities of rainfall were released.

Later in the month the southerly flow intensified, with a high pressure system to the east of the UK over continental Europe providing a block to the normal passage of the westerly jet. With colder than usual ocean temperatures over the northern part of the North Atlantic (see above), a strong temperature gradient formed which acted to strengthen the jet and set up the conditions for the formation of rapidly deepening cyclones, such as Storm Frank. These cyclones drew in warm, moist air from far south leading again to heavy rainfall and further flooding on already saturated ground. And the southerly winds on the eastern flank of Storm Frank, and strengthened by the high pressure to the east, enabled extremely warm air to penetrate, temporarily, the deep Arctic leading to very high temperatures.

Surface pressure chart 0001 30 December 2015

Surface pressure chart 0001 30 December 2015

The potential for December to be stormy and wet was picked up in the three-month outlook and is consistent with what we expect in early winter when there is a strong El Nino in place. However, early analysis suggests that the specific nature of this December’s extreme weather might be linked to the detailed structure of this El Nino, to the warmth of the north-east Pacific Ocean and to their combined effects on the atmospheric circulation.

As for whether climate change has played a role, we know that the overall warming of the oceans increases the moisture content of the atmosphere by around 6% for every 1°C warming. This extra moisture provides additional energy to the developing weather system, enabling even more moisture to be drawn in to the system, so that the overall enhancement of rainfall when the moisture-laden air impinges on the mountains of Wales, northern England and Scotland may be even more significant. So from basic physical understanding of weather systems it is entirely plausible that climate change has exacerbated what has been a period of very wet and stormy weather arising from natural variability.





Typhoon Dujuan strikes Taiwan

28 09 2015

Typhoon Dujuan has today (Monday 28 September) made landfall over Taiwan on the western rim of the Pacific Ocean with sustained winds well in excess of 100 mph. Dujuan is expected to drop large amounts of rainfall – 500mm is possible – over the mountainous interior of the island which could result in serious flooding and landslides. Within the first few hours of the typhoon affecting Taiwan 142mm of rainfall has already been recorded in Taipei.

Dujuan comes just seven weeks after Typhoon Soudelor struck the same part of northern Taiwan with a similar intensity. Soudelor caused flooding, destruction due to strong winds and some loss of life. Dujuan is expected to take a similar track to Soudelor – crossing the Taiwan Strait and reaching the Pacific coast of mainland China tomorrow (Tuesday 29 September) before moving inland.

Typhoon Dujuan just prior to landfall on 28 September 2015 Image courtesy of JMA

Typhoon Dujuan just prior to landfall on 28 September 2015
Image courtesy of JMA.

Typhoon Dujuan after making landfall on 28 September 2015 Image courtesy of MTSAT

Typhoon Dujuan after making landfall on 28 September 2015
Image courtesy of MTSAT.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dujuan and Soudelor are two of many strong typhoons and hurricanes which have occurred across the Pacific Ocean this year. One of the main contributing factors to the high level of storm activity is the strong El Niño which has developed. This is characterised by a marked warming of the tropical east Pacific Ocean. A strong El Niño can alter weather patterns in many parts of the world and in particular results in increased Pacific tropical cyclone activity. The last time an El Niño of the current strength occurred was in 1997-8 when high levels of Pacific tropical cyclone activity were also experienced.

In total there have been 43 tropical cyclones across the whole of the Pacific Ocean this year. 19 of these have acquired ‘major’ status – category 3 or above on the Saffir-Simpson Hurricane Wind Scale. The northern hemisphere season usually continues through October and November and in some seasons extends into December as well.

In addition to Typhoon Dujuan there are also two other tropical storms in the Pacific at present. Tropical Storm Niala is located in the central Pacific just south of Hawaii. It is not expected to impact Hawaii directly as it gradually weakens. The central part of the North Pacific Ocean surrounding Hawaii has seen a record number of tropical storms form this season, although Hawaii itself has avoided a direct strike from any of the storms so far.

Over in the far eastern Pacific Ocean Tropical Storm Marty is just under hurricane strength and is moving slowly towards the coast of Mexico. It is not certain yet whether Marty will make landfall, but a tropical storm watch has been issued for coastal areas including the resort of Acapulco.

Official warnings for the latest tropical cyclones in the western North Pacific are produced by the Japan Meteorological Agency. Central Pacific warnings are issued by the Central Pacific Hurricane Center and east Pacific and Atlantic warnings by the US National Hurricane Center. The Met Office routinely supplies predictions of cyclone tracks from its global forecast model to regional meteorological centres worldwide, which are used along with guidance from other models in the production of forecasts and guidance. We also provide updates on current tropical storms via @metofficestorms on Twitter.





Active Pacific tropical cyclone season continues

2 09 2015

Early September marks the half way point in the northern hemisphere tropical cyclone season and is often the time when we see the highest levels of activity – so how is this season shaping up?

As reported in a news release last week, tropical cyclone activity across the north Pacific has been extremely high this year with numerous intense typhoons in the west Pacific and hurricanes in the east Pacific. These are different names for the same thing – hurricanes occur east of the International Dateline and typhoons to the west.

There has been a fair amount of discussion recently in social and news media as to how ‘record-breaking’ this season has been so far. Reliable records only go back to about the 1960s or 1970s when satellite coverage of the tropical oceans became available. However, bearing this in mind, here are some of the remarkable statistics for the year up to 1st September:

  • There have been 15 tropical cyclones in the northern hemisphere reaching category 4 or 5 on the Saffir-Simpson Hurricane Wind Scale – 6 more than the previous record.
  • Tropical cyclone activity across the northern hemisphere as measured by Accumulated Cyclone Energy (a combined measure of intensity and longevity) is 200% of normal and over 20% above any other year.
  • Six hurricanes have crossed the central Pacific region – more than any other year.
  • Three north Pacific hurricanes have crossed the International Dateline – more than any other year.
  • Hurricanes Kilo, Ignacio and Jimena were all at category 4 simultaneously in the Pacific east of the International Dateline – the first time three major hurricanes have been recorded at the same time in this region.
IDL TIFF file

(L-R) Hurricanes Kilo, Ignacio and Jimena on 30 August 2015. Image courtesy of NASA.

Why the high levels of tropical cyclone activity?

One of the main contributing factors is the strong El Niño which has developed. This is characterised by a marked warming of the tropical east Pacific Ocean. Temperature anomalies here are currently at their highest since 1997-98, when high levels of Pacific tropical cyclone activity were also experienced.

What about the Atlantic?

The existence of El Niño conditions usually results in a quiet Atlantic hurricane season. This is primarily as a result of strong wind shear (winds varying in strength and direction with height) across large parts of the region. There have been six Atlantic tropical storms so far this season. Recently Danny became a major hurricane just east of the Caribbean, but quickly succumbed to the strong wind shear as it entered the Caribbean Sea. Erika threatened to develop into a hurricane, but again dissipated in the Caribbean due to a combination of high wind shear and interaction with islands such as Hispaniola.

In the far eastern Atlantic, conditions were favourable enough for a hurricane to quickly spin up as a cluster of thunderstorms moved off the west coast of Africa a few days ago. Fred became the most easterly forming hurricane in the tropical Atlantic Ocean and the first recorded hurricane to hit the Cape Verde Islands since 1892. However, as Fred has continued to move north-westwards it has also been subject to strong wind shear and is weakening rapidly.

What about the rest of the year?

Seasonal model predictions suggest that the strong El Niño will persist for several months to come. Hence it is likely that the high tropical cyclone activity in the Pacific will continue for the remainder of the season. The Atlantic is expected to have a quiet season overall, but this does not exclude the possibility of the development of a major hurricane. There are notable instances of damaging hurricanes occurring in otherwise quiet seasons such as Hurricane Andrew in 1992 which caused devastation in Miami, Florida.

Official warnings for the latest tropical cyclones in the western North Pacific are produced by the Japan Meteorological Agency. Central Pacific warnings are issued by the Central Pacific Hurricane Center and east Pacific and Atlantic warnings by the US National Hurricane Center. The Met Office routinely supplies predictions of cyclone tracks from its global forecast model to regional meteorological centres worldwide, which are used along with guidance from other models in the production of forecasts and guidance. We also provide updates on current tropical storms via @metofficestorms on Twitter.

Statistics on recent northern hemisphere tropical cyclone activity are courtesy of Dr. Phil Klotzbach of Colorado State University (@philklotzbach).





Predictions of a below average Atlantic hurricane season

21 05 2015

The Met Office Atlantic tropical storm forecast for 2015 is for eight tropical storms between June and November, with a 70% chance (the ‘70% range’) that the number will be in the range six to ten. This is below-normal relative to the 1980–2010 average of 12 tropical storms.

The forecast number of hurricanes — tropical storms with winds of at least 74 mph — is five (70% range three to seven); the average number of hurricanes is six.

Tropical storm Ana on 8 May 2015 as it approached the South Carolina coast. Credit: NASA Earth Observatory

Tropical storm Ana on 8 May 2015 as it approached the South Carolina coast. Credit: NASA Earth Observatory

The forecast Accumulated Cyclone Energy (ACE) index — a measure of the strength and duration of storms over the season — is 74 (70% range 40 to 108); the average ACE index is 104.

The North Atlantic hurricane season typically runs from June to November, but has already seen one tropical storm (Ana) make landfall in South Carolina.

The evolution of the El Niño Southern Oscillation (ENSO) over the next few months will play a large part in the North Atlantic hurricane season.

Forecast centres around the world have now declared that an El Niño has begun in the tropical Pacific.

Joanne Camp, climate scientist at the Met Office, said: “El Niño conditions in the Pacific can hinder the development of tropical storms in the Atlantic, so how this develops will be important for the storm season ahead.”

While it is still too early to determine with confidence how strong this El Niño might be, forecast models from centres around the suggest this El Niño is likely to strengthen during the coming few months.

The tropical storm forecast is produced using the Met Office’s seasonal forecast system, GloSea5.

It has higher resolution than its predecessor, with better representation of the complex physical processes that cause tropical storm and hurricane development.

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





Extreme global weather

5 01 2015

The UK may be experiencing what looks likely to be a milder than average winter but other parts of the globe are struggling against some extreme weather conditions.

Middle East

Heavy snow is expected to affect large parts of Turkey, Georgia, Armenia and SW Russia early this week. As the cold conditions spread east later in the week, strong to gale force winds and heavy snow are expected across more eastern parts of the Mediterranean.

This will lead to the Middle East seeing temperatures 10 or 15C below normal for the time of year. For example, overnight temperatures could fall to -10C in Syria by mid week, with daytime temperatures struggling to rise above freezing.

This is likely to have a significant impact on refugees and the humanitarian aid agencies in Turkey, Jordan, Lebanon, Syria and Iraq, with problems enhanced by the threat of frozen water supplies. Although overnight temperatures of -5 to -10C are expected, these values may well fall much lower if there is snow cover.

North America and Canada

Large areas of the USA and Canada are experiencing very cold conditions, with the threat of heavy snowfall across some parts over the coming days.

The eastward movement of a cold front over the weekend has dragged very cold air down from the arctic. Temperatures across parts of Canada have fallen to -30C, and widely across North America, daytime temperatures have ranged between 0 and -6C, with the bitterly cold conditions enhanced by strong winds.

As well as the low temperatures, some parts have seen heavy snowfall, such as the Pacific Northwest and areas to the east of the Great Lakes.

Further heavy snowfall is expected this week, particularly down-wind of the Great Lakes due to “lake effect” snow. This is caused when cold flows across relatively warm bodies of water such as the Great Lakes. The air rises in strong convective currents which creates clouds and heavy precipitation. In these very cold conditions, the moisture in the clouds will fall as snow.

Lake Superior (top left) and Michigan (centre) can be seen generating 'lake effect' snow. Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

Lake Superior (top left) and Michigan (centre) can be seen generating ‘lake effect’ snow. Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

The significance of this is highlighted by snowfall projections over the coming days. Lake Ontario, the easternmost of the Great Lakes with a surface area of 18,960 km2, is expected to bring narrow bands of heavy snow to areas east of the lake. These narrow bands could generate 2-3 feet of fresh snow over the next 24-36 hours causing significant disruption.

Whilst the freezing temperatures are expected to last throughout the week, temperatures may recover slightly through the weekend.

Will the US weather affect the UK?

The cold conditions will have the effect of strengthening the jet stream, which will move close to the UK over the coming days. This will bring unsettled conditions through this week, with spells of wet and windy weather, particularly across northwestern parts of the country. However, it will be mild, particularly towards the end of the working week when daytime temperatures could reach around 14C.

There is the potential for the remnants of this cold air to move eastwards across the Atlantic to affect the UK over the weekend. However, the airmass will become heavily modified by the Gulf Stream, and there is little risk of the extreme temperatures over North America affecting the UK.





How will activity in the Atlantic affect UK weather?

15 10 2014

There’s lots of activity going on in the Atlantic at the moment – but how will it affect the UK?

Currently there is a big area of low pressure covering a large part of the Atlantic between North America and the UK.

While it is fairly large in its size, it’s not particularly intense, powerful or unusual.

Forecast chart for 1pm on Wednesday 15 October 2014, showing large area of low pressure in the Atlantic.

Forecast chart for 1pm BST on Wednesday 15 October 2014, showing a large area of low pressure in the Atlantic.

This means that – while it may look impressive on the charts – it’s not going to bring anything out of the ordinary for the UK over the next few days.

It will, however, be generally unsettled across many parts through Friday and the weekend, as the low pressure drives a weather system across the UK.

This will bring strong winds, with gusts of up to 50mph in the most exposed parts of the west, and rain in places. However, some parts will enjoy periods of drier and brighter weather.

Tied up in the general Atlantic circulation is an area of warm air which was originally part of tropical storm Fay.

This will bring very mild air across parts of the country, with daytime temperatures possibly reaching around 20C across southeastern areas by Saturday, well above the October average for the region of 15C.

While it will be very mild, it may not feel particularly warm given the windy and often wet conditions. The unsettled weather is expected to be fairly standard for the middle part of October.

Forecast track of Gonzalo from the US National Hurricane Center.

Over the other side of the Atlantic near Bermuda, Hurricane Gonzalo is currently expected to track north and then east across the ocean over the coming days.

There is large uncertainty about the potential track of this storm, with some models suggesting that the remnants could move across the UK whilst others show them staying away from our shores.

If the ex-tropical storm does move across the country, some parts could see gales and heavy rain, but currently extreme conditions look unlikely.

As ever, we’ll keep a close eye on developments over the next few days and keep everyone up to date if it looks like there is any sign of severe weather heading for the UK.





Arthur becomes first Atlantic hurricane of the season

3 07 2014

Hurricane Arthur has become the first hurricane of this year’s Atlantic season, which started at the beginning of June.

Arthur is currently located close to the coast of south-eastern USA and is expected to move north-east, parallel to the coast, in the next few days.

Although the centre of the hurricane may only graze the coast it is likely to produce a storm surge several feet above normal tide levels and cause strong surf and rip currents along stretches of the US east coast.

Hurricane warnings have been issued by the National Hurricane Center for the North Carolina coast.

Hurricane Arthur - Image from NASA’s Aqua satellite courtesy of Colorado State University

Hurricane Arthur – Image from NASA’s Aqua satellite courtesy of Colorado State University

Seasonal forecasts for the Atlantic mostly indicate that there is likely to be a slightly below normal level of activity this season.

The Met Office forecast is for the most likely number of tropical storms in the season to be 10 with six of these likely to become hurricanes.

Further details can be found in our North Atlantic tropical storm seasonal forecast web page.

Meanwhile in the west Pacific a tropical depression has formed just south of the island of Guam.

This is expected to strengthen into a powerful typhoon over the weekend and could potentially threaten parts of Japan or Korea by the middle of next week.

Official forecasts of Atlantic and east Pacific tropical storms are provided by the National Hurricane Center.

Official warnings of west Pacific tropical storms are produced by the Japanese Meteological Agency (JMA).

The Met Office routinely supplies predictions of cyclone tracks from its global forecast model to regional meteorological centres worldwide, which are used along with guidance from other models in the production of forecasts and guidance.

Met Office StormTracker provides a mapped picture of tropical cyclones around the globe with access to track history and six-day forecast tracks for current tropical cyclones from the Met Office global forecast model and latest observed cloud cover and sea surface temperature. We also provide updates on current tropical storms via @metofficestorms on Twitter.





Met Office predicts below average Atlantic hurricane season

22 05 2014

The Met Office Atlantic tropical storm forecast for 2014 is for 10 tropical storms between June and November, with a 70% chance that the number will be in the range 7 to 13. The long-term average over the period 1980–2010 is 12 tropical storms.

Specifically for hurricanes (storms with winds of at least 74 mph) the best estimate is 6, with a 70% chance that the number will be in the range 3 to 9; the 1980–2010 average is 6 hurricanes.

The most likely value for the Accumulated Cyclone Energy (ACE) index — a measure of the strength and duration of storms over the season — is 84, with a 70% chance that the index will be in the range 47 to 121; the 1980–2010 average ACE index is 104.

An image of Hurricane Sandy taken on October 28, 2012.  CREDIT: NOAA/NASA GOES Project.

An image of Hurricane Sandy taken on October 28, 2012. CREDIT: NOAA/NASA GOES Project.

The evolution of the El Niño Southern Oscillation (ENSO) over the next few months will likely play a large part in the North Atlantic hurricane season.

Joanne Camp, climate scientist at the Met Office, said: “El Niño conditions in the Pacific can hinder the development of tropical storms in the Atlantic whereas La Niña conditions can enhance tropical storm activity, so how these conditions develop will be important for the storm season ahead.”

Current evidence from observations and forecast models indicates a 70% chance of an El Niño event developing this year, with thresholds likely to be reached by the peak of the hurricane season. This is no guarantee, however, that El Niño conditions will occur.

The tropical storm forecast is produced using the Met Office’s new seasonal prediction system GloSea5.

It has higher resolution than its predecessor, with better representation of the complex physical processes that cause tropical storm and hurricane development.

The forecast also uses information from the seasonal prediction system of the European Centre for Medium-Range Weather Forecasts (ECMWF).

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





Our change in the weather and how the jet stream is driving it

13 12 2013

After a quiet spell of weather courtesy of a slow moving area of high pressure, we are now entering an unsettled period as a series of Atlantic depressions are expected to pass close to the northwest of Britain during the next week.

High pressure has now moved away and is settled over Europe and a powerful jet stream is developing over the Atlantic which will be the main driving force behind this spell of unsettled weather.

What is the jet stream?

The jet stream is a band of fast moving westerly winds high up in the atmosphere which circle around the pole in the northern hemisphere. It can feature winds of up to 200 knots (230 mph) or more, and these winds tend to guide wet and windy weather systems which come in off the Atlantic.

The jet moves around a fair bit and its position can have a big impact on weather here in the UK depending on where it is.

If the jet is over the UK or just to the south, we tend to get a lot of wet and windy conditions as it brings weather systems straight to us. If the jet is to the north of us, it guides that changeable weather away to the north to leave the UK with more settled conditions.

What’s the jet stream doing now?

Unsurprisingly given the outlook for the next week, with a succession of Atlantic depressions passing by to the northwest of Scotland, the jet is positioned to the northwest of the UK too.

As you can see from the picture below, the jet currently swoops east from Canada – swinging northeast over the Atlantic towards the UK.

Forecast position of jet stream at midday Saturday 14 December 2013

Forecast position of jet stream at midday Saturday 14 December 2013

Closer to the ground very cold air is also streaming south from Canada and meeting warm air moving north from the Caribbean. It is where these two air masses meet under the jet stream that powerful Atlantic depressions form and are blown across the ocean towards our shores.

It is these depressions that bring a significant risk of severe gales and heavy rain affecting at least the northwest of the UK at times.

What’s the weather outlook?

Currently, Met Office National Severe Weather Warnings have been issued for wind across some northwestern and northern areas for the weekend. Gusts of 60-70 mph are likely with a risk of gusts to 80 mph or more across exposed parts of northwest Scotland.

However, at this stage there remains uncertainty regarding the extent of the strongest winds and these warnings will be updated as the weather develops over the weekend.

Looking ahead, while we expect further depressions to develop it is not possible to say exactly how vigorous they may be or pinpoint where they will be in a week’s time. This means it is too early to say which areas will experience the strongest winds and heaviest rain, however there are indications that  areas further to the south of the UK may be affected at times.

You can stay up to date with what to expect with our detailed forecasts out to 5-days and our weather warnings, as well as a general view of what we expect out to 30 days and find out what to do in severe weather

You can find out more about the jet stream in our YouTube video.

 





Guest blog – How the Atlantic may influence wet summers

19 06 2013

This morning there has been a lot of media coverage following a workshop held here at the Met Office HQ in Exeter on a recent run of unusual seasons in the UK.

Much of this centred around recent research by the University of Reading, presented at the workshop yesterday, which suggested Atlantic ocean cycles – specifically one known as the Atlantic Multidecadal Oscillation (AMO) – can have an influence on UK summer weather.

Here Professor Rowan Sutton, from the University of Reading, explains that research in a bit more detail:

 

“Last year, Buwen Dong and I at the National Centre for Atmospheric Science published a paper in Nature Geoscience about the link between slow changes in the temperature of the North Atlantic Ocean and weather patterns.

In particular, we presented evidence of a link between warm surface temperatures in the North Atlantic and a higher frequency of wet summers in the UK and Northern Europe.

This research built on earlier research I published with another colleague, Dan Hodson, in Science in 2005 and an important study by Jeff Knight and colleagues at the Met Office, which was published in 2006.

In our 2012 paper we showed that a rapid warming of the North Atlantic Ocean which occurred in the 1990s coincided with a shift to wetter summers in the UK and northern Europe and hotter, drier summers around the Mediterranean. The pattern identified matched that of summer 2012, when the UK had the wettest summer in 100 years.

Observational records show that the surface temperature of the North Atlantic has swung slowly between warmer and cooler conditions, and the present warm phase has a similar pattern to warm conditions that persisted throughout the 1930s, 40s and 50s. During the 1960s, 70s and 80s cooler conditions prevailed.

Computer simulations suggest that these changes in ocean temperature affect the atmosphere above. Warmth in the North Atlantic causes a trough of low pressure over western Europe in summer and steers rain-bearing weather systems into the UK.

An important question of interest to many people is how long will the current pattern of wet summers in northern Europe persist? This is a key research question and we don’t yet have precise answers.

In our 2012 paper we stated: “Our results suggest that the recent pattern of anomalies in European climate will persist as long as the North Atlantic Ocean remains anomalously warm.”

How long might this be?  There is strong evidence linking the swings in the Atlantic Ocean surface temperature to the “overturning” or “thermohaline” circulation of the Atlantic.

This circulation appears to have intensified in the 1990s. Following such a strengthening, a subsequent weakening is expected, as various feedbacks exert their influence.

For example, the surface warm waters transported northward by the overturning circulation have relatively low density which inhibits their tendency to sink, and acts to slow the circulation. Such a slowing cools the North Atlantic.

The time scales involved are in the range between a few years and a decade or two.  Progress in Decadal Forecasting, such as the pioneering work at the Met Office, and critical observations such as from the NERC-funded “RAPID” array, should help us to reduce this large range of uncertainty, but it is a challenging problem and advances may take some years.”








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