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).





So what happened to our summer?

28 08 2015

Our Chief Scientist Professor Dame Julia Slingo OBE FRS reflects on this summer’s weather and what has influenced it:

No-one can deny that we have had a pretty disappointing summer with a lot of unsettled weather and only a few warm spells, especially through July and August. Our weather has been dominated by low pressure over and to the west of the country that has brought us periods of heavy rain from the south – what we call the Spanish Plume. So what has been happening?

If we look beyond our shores there have been some big changes in the global climate this year. El Niño is in full flight, disturbing weather patterns around the world. The low pressure that has dominated our weather is part of a pattern of waves in the jet stream around the world that has brought crippling heat waves to places like Poland and Japan. And, looking back over past El Niños, you could have expected that a more unsettled summer might be on the cards for the UK. Closer to home the North Atlantic is more than 2 degrees colder than normal. It seems quite likely that the unusually cold North Atlantic has strengthened and pushed our jet stream south, also contributing to the low pressure systems that have dominated our weather.

So could all this have been anticipated? Seasonal forecasts for this summer suggested that temperatures and rainfall would be near normal. However, as the season progressed all the leading models around the world failed to capture the signal for unsettled weather over the UK. We all know that forecasting months and seasons ahead is still in its infancy and much more research needs to be done. On the other hand our day-to-day forecasts have been really successful in allowing us to warn of bad weather, highlighting yet again the benefits of our research that has delivered year-on-year and decade-by-decade improvements in forecasting skill. Our 5-day forecast is now as accurate as our 1-day forecast was when I started my career. This enables us to make so many decisions that keep us safe, protect our property, keep our infrastructure running and even when to go out and enjoy the sunshine!

All of this cannot happen without improvements to research and technology, and this week the first phase of our new supercomputer went live, five weeks ahead of schedule. This will enable us to provide even more accurate and relevant weather and climate forecasts to all of us, our government, emergency responders, and our many other customers at home and abroad.

The news that the BBC has decided that the Met Office won’t be their main weather provider when the current contract ends has raised the question of where will the new provider get their information from. It’s important to understand that no weather forecasting organization, whether it is a National Met Service like the Met Office or an independent company, can provide a service without a forecast, and that it is the leading meteorological agencies, like the Met Office, that build and deliver those forecasts. So whoever the BBC chooses to deliver their weather services in future, you can be sure that Met Office observations and forecasts will continue to be at the heart of them. We are committed to driving forward the skill and usefulness of our forecasts and ensuring that all of us benefit from the advances the Met Office makes in the coming years with our new supercomputer.





First hurricane for Florida since Wilma ten years ago

26 08 2015

Tropical Storm Erika was around 390 nautical miles east of Antigua on Wednesday morning and is moving west at around 18mph. The storm is expected to track close to Puerto Rico and the Lesser Antilles  on Thursday and then towards the Bahamas or South Florida by the end of the weekend, by which time Erika will probably have developed into a Hurricane.

The official guidance from Miami is for Erika to gradually strengthen to a category 1 hurricane by the start of next week. Erika will be the second hurricane of the 2015 season. Hurricane Wilma, in October 2005, was the most intense hurricane recorded in the North Atlantic, with an estimated central pressure of 882 mb.

Image courtesy of National Oceanic and Atmospheric Administration

Image courtesy of National Oceanic and Atmospheric Administration

As well as potentially damaging winds, Erika is likely to produce very heavy rainfall and a modest storm surge.

When Erika passes over the Lesser Antilles on Thursday there is expected to be 120mm of rainfall in 24 hours, but as Erika deepens near to the Bahamas and South Florida, totals of up to 400mm in 24 hours could occur, although there is some uncertainty in the exact location and intensity of Erika at this stage.

It is 10 years since Hurricane Katrina made landfall in Florida. It was the most costly hurricane on record causing an estimated $108 billion in damage in Louisiana and Mississippi. It also caused an estimated 1500 deaths. The strongest winds  were recorded during 25-30 August 2005  and were over the coastal areas of Louisiana and Florida.

No major (cat 3 or above) hurricane has made landfall on the USA since Wilma in October 2005. As for cat 1/2 hurricanes over the USA, Arthur just made landfall in 2014 (glancing blow to N Carolina) and in 2012 Isaac made landfall over New Orleans.  Although technically not a hurricane, Sandy had hurricane force winds at landfall over New Jersey. Other US hurricane landfalls since 2005 have been Irene in 2011, Dolly, Gustav and Ike in 2008 and Humberto in 2007.





Taiwan preparing for violent Typhoon

4 08 2015

A Typhoon is expected to bring flooding to parts of Taiwan and eastern China later this week with 500-700mm of rain forecast. Typhoon Soudelor is at the moment moving through the northwestern Pacific Ocean and looks likely to track across central Taiwan on Friday before making landfall over eastern China as it weakens.

This is a violent typhoon and is presently 500 miles to the west of the Northern Mariana Islands in the northwestern Pacific Ocean and is moving towards Taiwan. Currently surface wind speeds are estimated to be 130 mph with gusts of 190 mph, although these speeds are likely to ease slightly before reaching Taiwan.

Picture courtesy of Japanese Meteorological Agency

Picture courtesy of Japanese Meteorological Agency

This storm brings the threat of a storm surge and high waves to coastal areas of Taiwan and the southern Ryukyu Islands by Friday, as well as very strong winds quite widely, including to the capital of Taiwan, Taipei. Torrential rain is also expected which will bring a risk of significant flooding with the potential for 500-700mm rain falling in some areas in a 24 hour period.

The exact track of the storm could change over the coming days; you can see the latest track of Typhoon Soudelor through Storm Tracker and by following @metofficestorms on Twitter.





Big waves and blustery winds for western coasts

3 08 2015

A low pressure system off to the west of the UK is generating some big waves which are set to affect western coasts through today and Tuesday.

Waves of between 2-4 metres (about 6-12ft) are expected through the peak of the swell early on Tuesday at exposed beaches in the South West.

There will also be some fairly strong winds tomorrow, with the potential for gale force gusts around coasts in western areas – which may make for difficult conditions for those camping.

With many people around the coasts for summer holidays, people are being urged to take care.

A spokesman for the RNLI said: “Large waves could make some normal coastal activities we take for granted significantly more risky; the force of surging water or breaking waves can easily knock you over and quickly and drag you out of your depth and once in the water it can be difficult to get out.

“Those particularly at risk from these conditions are walkers on beaches or harbour walls when the water is high; spectators looking at the waves who get too close; and anglers fishing from rocks or exposed headlands.  With a low pressure and high winds forecast, areas that you may have considered safe before could be underwater when large waves come ashore.

“If you are planning a coastal activity, our advice is to respect the water;  watch the shore from a safe distance and assess the conditions – think about the risk before deciding if  you need to go closer.”

The waves are the result of a low pressure which is currently to the west of Ireland. As it has been tracking across the Atlantic its strong winds have been generating large waves.

Pressure chart showing the location of the low pressure at 0100 HRS on Monday morning, where it is generating large waves which are heading for western coasts.

Pressure chart showing the location of the low pressure at 0100 HRS on Monday morning, where it is generating large waves which are heading for western coasts.

As the low gets closer to the UK it will track to the north of Scotland, but the waves it has generated will continue marching east towards our coasts.

The size of the waves on any given beach will depend on a number of local factors.

Tides are not particularly large at the moment, meaning the risk of coastal flooding is low for the next few days despite the big waves.

A spokesman for the Environment Agency said: “The flood risk is very low for the next few days. We always monitor the situation closely, working alongside partners, including the Met Office and local authorities, and issue alerts and warnings if required. People and businesses can sign up to receive these free flood warnings and to check their flood risk via our daily flood risk forecast and live Flood Warnings map.”

With British and Irish waters being dangerously unpredictable, the RNLI have just launched a new campaign ‘Respect the Water’ to raise awareness of hidden dangers around our coastline.

For more information on ‘Respect the Water’ visit http://rnli.org/safety/respect-the-water/Pages/what-is-respect-the-water.aspx





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.








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