One metre of rain to fall in the Bay of Bengal

29 07 2015

Parts of the Ganges Delta have already seen over 240mm of rain in just 24 hours and coastal areas to the north of the Bay of Bengal are expected to receive over 1000mm over the coming 48 to 72 hours. The area will also see some strong winds, with gust of up to 60mph along the coast. This severe weather is likely to have significant impacts with a risk of flooding, landslides and damage to infrastructure.

Satellite image of monsoons over Pakistan, Bay of Bengal, and South China

Satellite image of monsoons over Pakistan, Bay of Bengal, and South China

After a break in monsoon rainfall across parts of India through much of July, the region is now experiencing a more active phase. Over the Bay of Bengal, a deep monsoon depression has developed, bringing a period of prolonged heavy rain and strong winds to coastal districts of northeast India, Bangladesh and northwest Myanmar. A monsoon depression is an area of low pressure which brings intense rainfall, and with other ingredients in place, can develop into a tropical cyclone.

The monsoon depression is expected to remain slow moving, tracking into Bangladesh over the next few days before gradually moving west across northeast India over the weekend.

Unusually, this is one of three monsoon depressions affecting South Asia. As well as the monsoon over the Bay of Bengal there is a monsoon bringing heavy rainfall to northwest India and Pakistan with as much as 430mm of rainfall falling in 24 hours. A third slow-moving depression is also affecting northeast Vietnam and southeastern China. 543mm 718mm has fallen in 42 66 hours in Mong Cai City on the border between Vietnam and China, an area that was affected by Tropical Storm Kujira last month.

Elsewhere in the world, the hot dry conditions which have affected southern Europe through much of July have led to some wildfires in Catalonia, Spain, and the Provence region of France. There is expected to be some respite from the high temperatures across Spain and France though in the coming days as a cold front pushes in from the north bringing a risk of heavy showers and thunderstorms to northeast Spain and Southern France by the weekend.

 





Has 2015 really been that windy?

24 07 2015

We’ve recently had several questions from the public asking whether this year has been particularly windy compared to others and if there’s any explanation for this. There’s lots of ways at looking at these questions, but the quick answer from our National Climate Information Centre is that – yes, it has been windy this year and a lack of high pressure seems to be to blame. Here Mike Kendon, climate information scientist at the Met Office, takes a detailed look at the questions.

How many calm days?

One way of looking at this is to consider how many days there have been which have not been windy – i.e. calm days – and how this compares with the historical record. The bar chart below counts the number of days each year, for the UK overall, where at least 20 weather stations have recorded a maximum gust speed of 10 Knots (11 mph) or less. This is equivalent to, at most, a gentle breeze, while 20 stations would indicate such conditions fairly widespread for at least 24 hours.

2015 thus far has seen only 8 such days; this being the fewest number of calm days across the UK for at least 20 years – but bearing in mind this covers less than 7 of 12 months of the year so far. However, more notably none of these days have fallen in May, June or July so far.

Chart showing the number of days per year where at least 20 UK weather stations have recorded a maximum gust speed <= 10 Kt (11 mph). 2015 data up to 22 July.

Chart showing the number of days per year where at least 20 UK weather stations have recorded a maximum gust speed <= 10 Kt (11 mph). 2015 data up to 22 July.

Pressure patterns

Calm days are typically associated with areas of high pressure, which normally bring dry, settled conditions during summer and cold, frosty conditions in winter – but common to both seasons often light winds. Areas of high pressure tend to block the prevailing westerly airflow across the UK. However, the variability of our climate means that some years see more days of high pressure, others see fewer such days.

The first map below shows the mean sea level pressure relative to average across the North Atlantic for the period January to June 2015. Over this 6-month period the pressure has been lower than normal to the north of Scotland but higher than normal to the south-west, resulting in a predominant westerly airflow over the UK, meaning that our weather has often been windy. Although during 2015 there have been some periods of high pressure, for example during March and early April, they have been relatively infrequent, particularly from May onwards. The pressure difference shown on the map between Iceland and the Azores is known as the North Atlantic Oscillation (NAO) index.

Pressure anomaly (difference from 1981-2010 average) in mb for the period January to June 2015 and January to June 2011, based on NCEP / NCAR Reanalysis data. Image provided by the NOAA/ESRL Physical Sciences Division.

Pressure anomaly (difference from 1981-2010 average) in mb for the period January to June 2015 and January to June 2011, based on NCEP / NCAR Reanalysis data. Image provided by the NOAA/ESRL Physical Sciences Division.

Rainfall patterns

A westerly airflow across the UK is generally associated with low-pressure systems from the Atlantic bringing windy conditions and rain-bearing fronts. Since this is the UK’s prevailing wind direction, the north-west is, on average, much wetter than the south-east, being most exposed to this direction. In addition, rainfall here is further increased due to the effect of hills and mountains.

During 2015, the persistent westerly airflow has resulted in this north-west / south-east contrast in rainfall patterns being exaggerated. For example, Achnagart, a weather station in the West Highlands of Scotland recorded 2082mm of rain in the period from 1st January to 22 July 2015, compared to 237mm for the same period at St James’s Park, Central London – 9 times as much.

The map below shows rainfall totals compared to average from January to June 2015. So, this rainfall pattern is consistent with this westerly weather type, absence of prolonged spells of high pressure, and relatively windy nature of 2015 so far.

Rainfall January to June 2015 as % of 1981-2010 average for that period.

Rainfall January to June 2015 as % of 1981-2010 average for that period.





A wet getaway

24 07 2015

As many of us plan to head off on holiday, heavy rain and strengthening winds cross southern England today (Friday), persisting overnight in the east, before clearing on Saturday morning.

A Yellow warning has been issued for southeast England and East Anglia, valid from Friday afternoon to 11am Saturday because of the potential impacts the heavy rain and wind could have.

 

Weather warning 24.07.15

As an area of low pressure is crossing northeastwards across the UK today (Friday), close to southern England, it deepens into quite an intense feature for this time of year and is expected to bring disruptive rain and wind, particularly within the warning area.

More than 30 mm of rain is expected quite widely, but there is a chance some isolated locations could well see more than 70 mm of rain. Wind gusts are also expected to be strong across the warning area, with northerly winds gusting to 45 mph inland and around 55 mph along coasts. This combination of factors could bring the risk of disruption to outdoor activities and heavy holiday traffic.
Highways England has launched a website especially for drivers heading to the South West of England to help plan their journey.





A summer forecasting challenge for Friday

22 07 2015

Forecasting rainfall for the UK during the summer has always posed a more difficult challenge than other times of year – and the weather for this Friday is a perfect example.

The various computer models the Met Office uses to forecast the weather differ on how a low pressure system forming to the west of the UK will behave.

We know that it will bring some wind and rain to the southern half of the UK, but there is no consensus on exactly which track it will take across the country and precisely when it will arrive.

Below you can see the area most likely to see some persistent rain during Friday and into Saturday. There is a 30% chance that rainfall could extend further north than this. The system is likely to bring up to 15-25 mm of rain and winds of up to 30 mph, mainly in exposed areas.

Forecast uncertainties 24-25-July

Currently there are no plans to issue a weather warning for this event, but clearly it has the potential to affect people’s plans for Friday now summer holidays are in full swing.  You can hear more about Friday’s forecast in the video below.

We’ll be keeping a close eye on the situation as it develops to ensure everyone has the clearest picture of what’s likely for Friday, so it’s worth staying up to date with the forecast over the next couple of days.

The current situation is a good example of why summer is tricky because at this time of year the details are vitally important.

Will the showers be inland or at the coast, when will low cloud clear to let warm sunshine through? In winter this might not be so important, but in summer when many are outside making the most of all the UK has to offer it can make a huge difference to your day.

Familiar features of our landscape such as hills, valleys or the sea can cause subtle variations in heat and moisture and therefore dominate the local weather outcome.  This can result in big differences in the weather in quite small areas, it can be sunny on the beach but raining inland or a village fair could be rained off while the next village down the road is dry.

At this time of year it’s always a good idea to keep a close eye on the forecast as the situation can change from day to day.

We’re always harnessing new science and technology to make forecasting ever more accurate and summer forecasting is a major focus for future gains.





Summer returns but no heatwave

2 06 2015

There have been some stories in the press that a heatwave is on the way later this week.  Although we are expecting temperatures to rise over the coming days with some pleasant early summer weather, any very warm weather will be fairly short-lived.

After an unseasonably cold, wet and windy start to June and the meteorological summer, high pressure is expected to build across southern parts of the UK from Wednesday, resulting in a much quieter and more pleasant spell of weather.

By Friday, a plume of hot air from the continent could bring temperatures in the mid 20s°C  across south eastern parts of the country, but this in turn is likely to trigger some thundery showers. So although temperatures are likely to peak on Friday, this may not necessarily be accompanied by blue skies and sunshine, as a good deal of cloud is possible along with rather humid and hazy conditions.

Deputy Chief Meteorologist Martin Young said “although things will be a good deal warmer than of late, there still remains considerable uncertainty about how hot it will be and exactly where will see the highest temperatures on Friday, and the public should keep in touch with the latest forecasts”.

This coming weekend is likely to see temperatures a little lower than Friday’s in the south east, but plenty of pleasantly warm sunshine is expected across much of the UK with temperatures widely in the high teens, and reaching the low 20s°C  in parts of the south.





Ten Tors

8 05 2015

This weekend sees the 2015 Ten Tors challenge and once again, the Met Office will be providing tailored forecasts for the organisers to help with event planning and coordination. This year, for the first time, an Operational Meteorologist will also be at Okehampton Camp for the weekend, providing the latest information on weather conditions across Dartmoor throughout the event to help the organisers make the necessary decisions to keep the teams safe.

Forecast

Chief forecaster Dan Suri said “The event may start on rather a wet note, with some heavy showers likely on Saturday morning”. These showers will clear later in the morning leaving a drier and brighter afternoon. It will be breezy too, making it feel quite chilly in the wind. Saturday night will be largely dry, but it is likely to become murky through the early hours of Sunday, with occasional drizzle and hill fog. The cloud base will probably lift a little during Sunday morning, but higher parts of the Moor are likely to stay murky, and whilst the odd brighter spell may develop with shelter from the wind, it will remain largely cloudy. Still quite breezy on Sunday too.

The challenge

The weather plays a major part in the successful completion of the event for everyone taking part. Around 400 teams of six take part in the challenge to complete the course. There are three different course lengths, depending on the age and ability of the team:

  • 35 miles
  • 45 miles
  • 55 miles.

The idea of the challenge is for the teenagers to become self-sufficient for the weekend – carrying everything they’ll need for the trek and making their own decisions.

At this time of year, conditions can be varied, from torrential rain to hot sunshine.

Ten_Tors_infographic_2015

For more information about the event, including the latest weather and a video explaining the variety of conditions you might expect on Dartmoor, take a look at our events pages.

Our National Park forecast service includes forecasts for a wide range of locations on Dartmoor, many of which are included within the Ten Tors event. You can also find forecast information on our weather pages.





Active tropical storm season in the Northwest Pacific as another typhoon heads for the Philippines

7 05 2015

Typhoon Noul is currently to the east of the Philippines in the Northwest Pacific, and is heading steadily west-northwest. Noul is expected to continue moving towards the Philippines whilst intensifying further to a very strong typhoon. The storm is expected to make landfall in the Philippines this weekend.

Noul pacific sat pic

There is still some uncertainty in the exact track, but currently Noul looks likely to make landfall on the east coast of Luzon, bringing very strong winds with gusts of 130kt (150mph), coastal and inland flooding with total rainfall accumulations of up to 400mm possible, and potential landslides across large parts of northern Luzon. There is also a risk of significant impacts in Manila if Noul takes a slightly more southerly track.

Track from Japan Meteorological Agency

Track from Japan Meteorological Agency

Although the typhoon is expected to weaken next week, Noul could also bring some heavy rain to parts of Japan.

This is the sixth tropical storm of the north-west Pacific season and the fourth to become a typhoon, which is an unusual level of activity so early in the season. And yet another tropical storm looks set to develop behind Noul, possibly following a similar path.

The Met Office works closely with counterparts at the Philippines weather service PAGASA, providing the latest information on computer model predictions of the likely track and intensity of Typhoon Noul as it nears the country.

Official warnings of west Pacific tropical storms are produced by the Japan Meteorological Agency. 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.





Two cyclones to hit Australia

19 02 2015

Whilst here in the UK, we are coming towards the end of our winter season, Australia is coming towards the end of summer, but is in the middle of its cyclone season, and unusually there are currently two tropical cyclones affecting the country.

Severe Tropical Cyclone Lam is currently to the north of Australia’s Northern Territory, in the Arafura Sea. The storm is expected to make landfall on Thursday as a category 4 storm, between Milingimbi and Gapuwiyak. Huge rainfall figures are forecast, with 300 to 600mm daily, potentially adding up to more than 800mm in places throughout the storm event, with flooding likely inland, as well as coastal flooding and damaging winds. Residents close to the coast have been advised to be ready to move to shelter with emergency kit. However, as the area is not densely populated, significant impacts are not expected. The nearest large population centre is Darwin, and although it is likely that there will be some wet and windy weather here, it is not expected to be anything that Darwinians aren’t used to.

Credit: Courtesy of the Naval Research Laboratory

Credit: Courtesy of the Naval Research Laboratory

Storm track and warning areas for Tropical Cyclone Lam

Storm track and warning areas for Tropical Cyclone Lam

Meanwhile, Severe Tropical Cyclone Marcia is heading towards the Queensland coast, and is expected to make landfall between Mackay and Gladstone on Thursday night as an extremely powerful category 5 storm. The Australian Bureau of Meteorology are forecasting Marcia to track inland for a while and quickly weaken, before turning parallel with the coast, which keeps the main risk area to the north of Brisbane. However, there is some uncertainty with the exact track of the storm, and if it were to remain closer to the coast, Brisbane could be in line for a significant amount of rainfall, potentially as much as 400mm. Destructive winds are likely around the coast and abnormally high tides will be experienced with water levels expected to rise above the highest tide of the year. Dangerous storm tides are forecast as the cyclone crosses the coast, as well as treacherous surf on exposed beaches.

Credit: Courtesy of the Naval Research Laboratory

Credit: Courtesy of the Naval Research Laboratory

Storm track and warning areas for Tropical Cyclone Marcia

Storm track and warning areas for Tropical Cyclone Marcia

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.





One year on – A look back to last winter

17 02 2015

This weekend marked the one-year anniversary of the Valentine’s Day storm, which also marked the end of a particularly stormy three-month period. A new review article – ‘From months to minutes – exploring the value of high-resolution rainfall observation and prediction during the UK winter storms of 2013/2014’ – written by 16 Met Office co-authors reviews the accuracy of our forecasting and warning of severe weather during winter 2013-14, and assesses its performance.

The paper concludes that the “prolonged period of high impact weather experienced in the United Kingdom during the winter of 2013/14 was very well forecast by the operational tools available across space and time scales.”

Here Huw Lewis, the paper’s lead author, and Derrick Ryall, Head of the Public Weather Service, look at the extreme weather last year and the role of the Met Office in communicating severe weather through the National Severe Weather Warning Service.

Analysis chart 1200 GMT 26 January 2014

Analysis chart 1200 GMT 26 January 2014

Winter 2013/2014 in the United Kingdom was remarkable. The country was battered by at least 12 major winter storms over a three month period and was officially assessed as the stormiest period that the United Kingdom has experienced for at least 20 years.

The series of storms resulted in the wettest winter in almost 250 years (according to the England and Wales precipitation series from 1766), significantly wetter than the previous wettest winter in 1914/1915.

Snapshot of UK rain radar surface rainfall rate for 2200 GMT on 23 December 2013

Snapshot of UK rain radar surface rainfall rate for 2200 GMT on 23 December 2013

The extreme weather caused widespread flooding throughout Southern England and coastal damage – most notably in the South West and Norfolk coasts. The impact of the severe winter storms on individuals, businesses and the government were substantial, including several fatalities, widespread power cuts and damaged infrastructure.

Recent advances in forecasting, technology and the scientific developments in meteorology have been considerable. These developments and improvements in accuracy mean that a four-day weather forecast is as accurate as a one-day forecast was just thirty years ago. During the course of last winter, the Met Office was able to use these forecasts to warn of any severe weather well in advance. In the case of the St Jude’s Day storm at the end of October 2013 warnings went out to the Government and the public five days before the storm even existed.

rainfall

As the accuracy of weather forecasts has evolved, so has the communication of the potential impacts of severe weather. The National Severe Weather Warning Service enables more ‘weather decisions’ which in turn help to minimise the consequences of severe weather. The Met Office was at the heart of the government response to the storms, providing advice on weather impacts through the National Severe Weather Warning Service and Civil Contingency Advisors. The Met Office also worked very closely with both the national and regional media, who in turn played a key role in ensuring that the public were fully informed about the potential impacts of any up-coming weather.

In addition to the Public Weather Service, commercial partners and customers were also provided with detailed updates throughout the period in order for them to plan effectively for logistical issues. Together, these advanced warnings helped authorities, businesses and individuals to be better prepared to take mitigating actions.

Driving further improvements in accuracy and therefore reducing the lead time and increasing the detail of severe weather warnings is one of the Met Office’s key priorities . The ultimate aim is to improve the potential for users to plan preventative measures for severe weather events much further ahead. Underpinning all of these developments is a continuing programme of scientific research and access to enhanced supercomputing over the next few years.





How a strong jet stream is affecting aviation

13 01 2015

We often talk about the jet stream and its impacts on UK weather – but it can have an even more direct effect on aviation as covered in the media in recent days.

The jet stream is a band of fast moving winds high up (around 5-7 miles) in the atmosphere. It usually travels eastwards around the northern hemisphere but regularly changes its track and strength.

Pilots travelling east, say from the US back to Europe, use the jet stream to cut journey times and save fuel – just like a cyclist uses a tailwind on a bike.

This has always meant journey times in the northern hemisphere are faster when travelling east than heading west (when airlines avoid the jet stream).

Recently the jet stream has been particularly strong over the north Atlantic, with winds of more than 250mph being seen at times.

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

This has had an impact on flying times – with eastbound trans-Atlantic services arriving well in advance of their scheduled times. Some types of passenger aircraft have reputedly seen record breaking journey times.

All this of course has a knock-on effect for airports as schedules are carefully planned to ensure there’s room, not to mention boarding gates, for each aircraft when it’s due to land. That has meant the strong jet stream creates a logistical challenge for airports across Europe.

The Met Office has been helping airlines and airports to plan ahead with its forecasts of the strength of the jet stream through its role as a World Aviation Forecasting Centre (WAFC).

There are only two WAFC centres in the world; the UK and Washington, in the US. The two centres provide aviation charts for the globe, highlighting conditions between 10,000 and 63,000 feet.

These charts show the location and strength of the jet stream, as well as other important aviation factors, such as clear air turbulence, cumulonimbus (storm producing) clouds, volcanoes and tropical storms. Both centres operate 24 hours a day and throughout the year.

Airlines use our upper-air wind forecasts to predict flight times at cruising altitude. For transatlantic flights during 2012, the average difference between the predicted flight time and the actual flight time was about one minute. This means that our aviation customers can accurately calculate the fuel load required for each flight. Our WAFC charts save airlines globally £2.7 billion a year because our forecasts help them fly safely and efficiently.

Accurate forecasts enable pilots, airlines and airports to assess flying times in advance and use that information to try to ensure things run as efficiently as possible on the ground.








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