The severe storm this weekend and why it’s not a hurricane

26 10 2013

There is much coverage of the storm heading our way later this weekend with mentions of it being a ‘hurricane’. This is not strictly correct as we don’t get hurricanes in the UK and this is why.

Hurricanes are warm latitude storms; they draw their energy from warm seas and can only begin to form where the ocean is warmer than 26 degrees Celsius or so, and can really only become a major storm when the sea is warmer than 28 degrees Celsius. That’s like a warm bath, so you won’t find one around the UK anytime soon!

Other limitations, like wind patterns in the upper atmosphere and the forces caused by the Earth’s rotation, mean hurricanes are normally found in an area between 8 and 20 degrees north of the equator.

You can find a full explanation of what hurricanes are and how they form on our What are hurricanes? video

The storm which is due to develop tomorrow night and affect the UK during Monday is a mid latitude storm, the sort which affect us through the autumn and winter. These are formed in a very different way – by the meeting of different air masses on what is known as the polar front, leading to low pressure (storms) forming, often around the latitude of the UK.

The storm which is due tomorrow is expected to bring very strong winds and heavy rain, and we are warning of winds gusting 60-80 mph quite widely and locally over 80 mph, especially on exposed coasts, both in the southwesterly winds ahead of the low centre and west to northwesterly winds behind it.

Winds of that strength are classified on the Beaufort scale as ‘hurricane force 12’ but that is not the same as being a hurricane. Winds of this strength could bring down trees or cause structural damage, potentially causing transport disruption or power cuts and we are working closely with the resilience community to ensure they are prepared for the expected conditions.

You can find practical advice about what to do in winter weather on our Get Ready for Winter website.





‘Spot on’ snow forecast supported by latest science from the Met Office

6 02 2012

Over the weekend our highly accurate forecasts of heavy snow and widespread ice enabled the country to prepare for the hazardous conditions helping to keep the country moving.

At Heathrow Airport, for example, snow arrived within ten minutes of when Met Office forecasters had predicted – giving vital guidance for those managing the situation.

This level of forecasting accuracy is far from easy to achieve, however. Snow is an example of a small-scale weather feature, affected by a number of variables and notoriously difficult to forecast.

The Met Office is using cutting-edge developments to improve the accuracy of forecasts in these challenging situations which deal with so-called ‘small scale’ weather.

This includes things like intense rain showers or thunderstorms – which can be just a few hundred metres across, or weather which depends on fine details of the land surface, such as snow or valley fog.

These types of weather can be very difficult to represent in forecasting models, which are the computer generated simulations of what the atmosphere – and weather – will do next.

Because the weather at a particular location is influenced by much larger scale weather patterns, models need to be run on a global scale even just to forecast for the UK.

Forecast models require a very large number of calculations and, with the computing power available, the global model the Met office runs uses a grid-scale of 25km (i.e. every grid-box is 25km x 25km).

At this resolution, large scale weather patterns will be well reproduced but the model will be unable to capture the detail of small scale weather. To tackle this, the Met Office has developed UKV.

This involves running a version of the model which focuses on the UK, allowing a much smaller 1.5km scale to be used. Information is fed in to the edges of UKV from the 25km global model.

The 1.5km grid-boxes enable UKV to capture things like snow much better, leading to improved forecasts in many situations.

In most situations, even with a 1.5km grid, current science and technology does not enable the prediction of the exact location and timing of each shower that passes over the UK. However, the increased detail gives a better indication of the character of the weather and could be useful for giving probabilistic forecasts – which give the chances of, for example, rainfall in a given place at a given time.

As well as the the 1.5km weather model helping with our forecasts in the last couple of days, they also helped with the accuracy of our snow forecasts in the very cold and snowy weather at the end of 2010. Back in November of that year, we saw numerous heavy snow-showers being carried inland from the sea in a NE wind caused significant disruption in the north east of England. The picture below shows that for the coarser 12 km model (NAE) showers stall over the coast causing a major underestimate of snow inland. This is a well known problem with models of this grid length. In contrast, the UKV is able to represent the showers more realistically and brings the showers inland, producing a much better forecast. The UKV better represents what actually happened as shown by the radar image to the left.

24 hour accumulations for 25 Nov 2010 from UKV and 12 km (NAE) models compared to that actually observed by radar. This shows an example of the advantages of a high resolution models

We are continuing to look at ways of even further improving the accuracy and detail of our forecasts. You can find a more in-depth article about UKV in our Research News section.





Australia recovers as Severe Tropical Cyclone Yasi finally weakens in Northern Territory

4 02 2011

 

Tropical Cyclone Yasi

Tropical Cyclone Yasi

Parts of North East Australia are clearing up in the wake of Severe Tropical Cyclone Yasi, which is likely to have been the most intense cyclone at landfall over Queensland since 1918.

Cyclones of a similar intensity have made landfall more recently elsewhere in Australia:

 

  • Tropical Storm Laurence in 2009
  • Tropical Storm Monica in 2006

Severe Tropical Cyclone Yasi reached the coast at Mission Beach at midnight local time on Thursday, with the nearby town of Tully experiencing most of the destruction. However, the larger towns of Cairns and Townsville were spared the worst of the damage.

Some of the facts and figures from Severe Tropical Cyclone Yasi:

  • Highest sustained winds were estimated to be near 155 mph, with higher gusts.
  • Lowest air pressure was 929 millibars recorded at Tully.
  • Five metre storm surge at Cardwell just south of Mission Beach.
  • It was the strongest cyclone globally since Super Typhoon Megi in October 2010 which struck the Philippines.

Six days prior to landfall on Thursday 27th January, the Met Office global model was able to predict the point of landfall to within 46 km. The storm was not actually named until Sunday 30th January and had to cross 3500 km of ocean to reach Australia. Subsequent forecasts of landfall had errors averaging close to 150 km – well below what is usually expected.

The Australian Bureau of Meteorology are responsible for cyclone warnings in this region and use their own version of the Met Office Unified Model to underpin their forecasting capability.

Casualty figures related to Cyclone Yasi so far are low and may even be zero. This is testament to the excellent forecasts and warning procedures and people heeding the warnings.





Met Office in the Media: 14 December 2010

14 12 2010

The current cold weather continues to feature across the media, with widespread coverage of the predicted return to arctic conditions on Thursday this week.  The Guardian reports that the ‘Weather set to take Arctic turn as big freeze returns to Britain’ whilst the Telegraph reports that ‘The second Big Chill set to last a month‘‎. Wales online have reported ‘Arctic blast blowing in on Thursday‘, whilst in Scotland, where there is the risk of significant snow showers in northern and western parts through Thursday and Friday, The Scotsman warns of ‘The disruption: Motorists warned to expect black Thursday’.

There has been much discussion today about whether we will see a White Christmas this year, with some other forecasters coming out and saying it is “guaranteed”. Most weather forecasters would agree that nothing is ever guaranteed in meteorology and regarding whether it will snow on December 25th it is still too early to provide a detailed forecast. More information is in a post made yesterday on a White Christmas.

Elsewhere there has been widespread coverage of new research by Met Office scientists on using lightning to measure the height of the plume emitted from erupting volcanoes. It is hoped this can be used to help in forecasting ash plume movements. EnvironmentalResearchWeb reported that ‘Volcanic lightning could help monitor plume height‘, along with MSNBC and The Economist.

We have also released verification of our North Atlantic Hurricane season forecast this week. The Met Office accurately predicted the above-average North Atlantic tropical storm season again this year, maintaining the excellent record of its forecast since it was introduced in 2007, and more detail can be found in ‘Continued success for tropical storm forecast’.

Finally, The Armstrong and Miller Show on BBC One on Saturday night used Met Office graphics to support a sketch about the difference between weather and climate. Ben Miller gave us a timely reminder that what is happening outside the window right now is ‘weather’, and the long-term trend averaged over many years is the ‘climate’. You can watch this on BBC iPlayer starting at 7 minutes and 5 seconds in.





Met Office Chief Scientist at the AGU Autumn Meeting

14 12 2010

The Moscone Conference Center, location of the AGU Fall Meeting

The Moscone Convention Center, location of the AGU Fall Meeting

They say that this is the biggest science meeting of any year and with just one look at the crowds surrounding the 2010 meeting in San Francisco it’s hard to argue against that.

Over 15,000 scientists representing every colour and creed of the geophysical disciplines are gathered at the huge Moscone Convention Center to deliver and debate the big topics of the moment.

The Met Office‘s Julia Slingo is among them. Our Chief Scientist is here at the American Geophysical Union Fall Meeting to deliver a presentation on what she sees as the scientific challenges facing society in making us more resilient to natural hazards.

We live a lifestyle that makes us increasingly vulnerable to all sorts of hazards, be they related to extreme weather or geological phenomenon such as the Eyjafjallajökull eruption. 2010 has provided the world with many examples of just how exposed we are to these kinds of event.

As well as that volcanic eruption that had such a devastating impact on air travel right across the world, extreme rainfall in Pakistan and China and record-breaking temperatures in Russia this past summer have caused tragically high loss of life and massive damage to the infrastructure of those countries. And currently the UK is in the grip of its worst early winter for many years. So what can be done to address this? 

In her talk, Professor Slingo says we need to be able combine work from different areas of science and deliver increased computing capacity to provide better answers to the problems faced by society today.

But more than this it is imperative we look at what computer weather and climate prediction models tell us in a different way. We should focus more on making a quantified assessment of the probability of a certain outcome so that we can provide the sort of advice needed to combat what may be an increasing frequency of such dangerous weather.

And while our models are by no means the finished article they do tell us some things well enough. High temperatures across parts of Russia were clearly signalled by seasonal prediction models and the risk of record-breaking extremes was identified in a small, but significant, number of the ensemble members.

Professor Slingo believes we have the basic building blocks required to deliver better predictions of weather extremes, but it is becoming increasingly obvious we need to link different scientific disciplines to fully counter the threats posed by them. Our increasing vulnerability makes that vital.








Follow

Get every new post delivered to your Inbox.

Join 5,943 other followers

%d bloggers like this: