Intense storm threatens Sydney

22 04 2015

Parts of New South Wales in southeast Australia have had severe flooding and wind damage over the past few days due to an intense low pressure system. Parts of the region have already seen more than 300mm (around a foot) of rainfall. Areas around Sydney have been affected, with flooding claiming three lives and causing evacuations of properties, as well as disrupting power and transport. Officials warned that hundreds of homes in the city are under threat from rising river levels, and it has been reported that the State Emergency Service (SES) have received nearly 10,000 calls for help and carried out more than 100 rescues.

Analysis chart from Austrlian Bureau of Meteorology

Analysis chart from Austrlian Bureau of Meteorology

The storm is now weakening and moving away southeastwards into the Tasman Sea, so conditions are expected to improve over the next 24 hours, however remnants of the system are likely to bring a further 50 to 75mm of rainfall to some coastal parts today, before conditions gradually become quieter.

Rapid Response image from NASA

Rapid Response image from NASA

For more information on current warnings and forecasts across New South Wales, visit the Australian Bureau of Meteorology website.





Powerful super-typhoon heads for Philippines

1 04 2015

There is currently a super typhoon in the western North Pacific called Maysak. This is a particularly strong storm for the time of year with winds in excess of 160 mph. The strongest storms in this region usually occur between August and October. Tropical storms, including typhoons, are reliant on sea surface temperatures for their energy, and as the northern hemisphere has just moved from winter to spring, this is the coldest time of year for sea temperatures. However, in the region where Typhoon Maysak formed just north of the equator, sea temperatures are almost always above 26°C, which is the critical value for tropical storm formation. Furthermore, the sea temperatures are unusually warm in this area by more than 2°C.

Super Typhoon Maysak is the fourth tropical storm of the season in the western North Pacific, the others being Mekkhala, Higos and Bavi. There has not been a year with four or more tropical storms in this region forming before the end of March since 1965. Three of the four storms have been typhoons – only Bavi remained below the 74mph threshold (the sustained wind speed required to become a typhoon). There have never been as many typhoons before the end of March in the era of reliable records (since World War II). Maysak was also the strongest typhoon to develop in March in this region since Mitag in 2002.

Typhoon Maysak as seen from the MTSAT satellite on 1 April 2015 Image courtesy of digital-typhoon.org

Typhoon Maysak as seen from the MTSAT satellite on 1 April 2015
Image courtesy of digital-typhoon.org

Maysak has now started to weaken as it moves west-northwest towards the Philippines. However, Maysak is still likely to be a typhoon when it makes landfall this weekend. There is still some uncertainty over the exact track of the storm, but the most probable path suggests the Philippines’ northern island, Luzon, is most at risk – including the capital Manila. Wind damage and flooding are likely, particularly in coastal areas.

Typhoon Maysak on 1 April 2015. Image courtesy of the US Naval Research Laboratory

Typhoon Maysak on 1 April 2015.
Image courtesy of the US Naval Research Laboratory

The Eye of the Storm

Air sinks at the centre of a typhoon, resulting in the formation of an ‘eye’ which is sometimes free of cloud and mostly calm. However, on occasions small scale rotations can develop within the eye causing distinctive ‘mesovortices’ (small scale columns of rotating air) in the low level cloud pattern. These can be seen in this satellite loop of Typhoon Maysak created by the Cooperative Institute for Meteorological Satellite Studies at the University of Wisconsin:

http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2015/03/MAYSAK_H8VIS_064_31March_end0600_fast.gif

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 Maysak 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, as well as the 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.





Very strong winds recorded over northern parts of the UK

9 01 2015

As forecast by the Met Office, a powerful low pressure system passed to the north of the UK in the early hours of this morning bringing exceptionally strong winds in places.

Two low level stations recorded wind speeds of over 100mph, with the gust recorded at Stornoway being the joint strongest recorded at the site (the other gust at that speed was recorded on 12 February 1962).

While the winds have now dropped significantly, it will stay windy through today in many parts and gusts will increase in strength once again tonight as another low pressure system is set to affect northern parts of the country. You can see detail on this on our forecast and warnings pages.

Below are some of the maxiumum gust speeds recorded during the first storm, between 10pm last night and 9am this morning.

Date and time Station Area Speed (mph)
09/01/2015 03:00 STORNOWAY AIRPORT WESTERN ISLES 113
09/01/2015 03:00 LOCH GLASCARNOCH ROSS & CROMARTY 110
09/01/2015 04:00 ALTNAHARRA SUTHERLAND 97
09/01/2015 06:00 WICK AIRPORT CAITHNESS 93
09/01/2015 03:00 ALTBEA ROSS & CROMARTY 90
09/01/2015 01:00 EDINBURGH BLACKFORD HILL MID-LOTHIAN 90
09/01/2015 00:00 SOUTH UIST RANGE WESTERN ISLES 90
09/01/2015 05:00 KINBRACE SUTHERLAND 87
09/01/2015 01:00 SKYE WESTERN ISLES 86
09/01/2015 07:00 KIRKWALL ORKNEY 86

The strongest wind in England was at High Bradfield, in South Yorkshire, which saw a gust of 76 mph at 1am this morning.

In Wales, the strongest gust was at Aberdaron, Gwynedd, with 76mph at 11pm last night.

For Northern Ireland, the strongest was 70mph at Killowen, County Down, at 10pm last night.

Winds are almost always stronger at our high level weather stations (those that are sited at 500 metres of altitude or higher), which are also often very exposed.  For this reason the winds from those sites are unlikely to reflect what the vast majority of people are experiencing. Bearing that in mind, the strongest gusts from the high level sites are quoted below for reference:

Date and time Station Area Height (metres) Speed (mph)
09/01/2015 04:00 CAIRNGORM SUMMIT INVERNESS-SHIRE 1237 140
09/01/2015 00:00 AONACH MOR INVERNESS-SHIRE 1130 129
09/01/2015 04:00 BEALACH NA BA ROSS & CROMARTY 773 124
09/01/2015 05:00 GREAT DUN FELL CUMBRIA 847 107
09/01/2015 05:00 GLEN OGLE PERTHSHIRE 564 102




A closer look at ‘weather bombs’

10 12 2014

With strong winds affecting parts of the country today, there has been a lot of talk about ‘weather bombs‘ – but what are they and what do they mean for our weather?

First of all, it’s important to stress the UK is not being ‘hit’ by a weather bomb – the track of the low pressure system is well to the north of the UK, on roughly the same latitude as Iceland. We’re feeling its influence remotely.

This means we are not getting the very strongest winds associated with this system, but far north-western parts of the UK are seeing winds in the 70-80mph range as forecast. Further south the winds are much less strong – so London, for example, is unlikely to see even gale force gusts and mean wind speeds will be much lower.

Another point is that the ‘bomb’ element, the rapid deepening of the low pressure as explained below, happened on Monday – and its now just like any other powerful Atlantic low. In fact, the weather we’ll experience today is nothing unusual for the time of year.

Chart showing a low pressure in the north-west Atlantic at midday on Monday 8 December.

Chart showing a low pressure in the north-west Atlantic at midday on Monday 8 December.

Chart shows the same system 24-hours later, with a 26 millibar fall in pressure.

Chart shows the same system 24-hours later, with a 26 millibar fall in pressure.

So what is a ‘weather bomb?’

A ‘weather bomb’ is more usually referred to as ‘explosive cyclogenesis’ and is a meteorological term describing the rapid fall in central pressure of a depression (or low pressure) – it has to fall by 24 millibars in 24 hours in our latitudes to meet the criterion.

In many ways a ‘bomb’ can be seen as simply a more powerful, more intense version of the kind of Atlantic low pressure systems that normally affect the UK.

Climatologically speaking, explosive cyclogenesis events, or bombs, tend to occur most frequently over sea near major warm ocean currents, for example over the North Atlantic Ocean near the Gulf Stream or over the Western Pacific Ocean near the Kuroshio Current.

An explosive cyclogenesis event in these regions would then tend to happen as a particularly intense jet stream (which is a narrow band of strong winds high up in the atmosphere) interacts with an existing, and often weak, low pressure lingering near one of these warm ocean currents.

In other words, as with so many things in meteorology, it is the coming together of multiple ingredients that allow a ‘bomb’ to develop.

How many ‘bombs’ a year – and what is the impact?

There are gaps in the global observational record, so it’s difficult to give a definitive number of how many ‘weather bombs’ are seen globally each year. However, recent estimates based on a twenty to thirty year dataset suggest there are somewhere between 45 and 65 explosive cyclogenesis events per year, with more ‘bombs’ occurring in the northern than southern hemisphere.

Of course, it’s important to realise that the definition of a ‘bomb’ is somewhat arbitrary and ‘just a number'; a depression deepening only slightly less than 24hPa in 24 hours will still be a powerful depression more than capable of producing severe weather.

Another important point is that the track a ‘bomb’ takes relative to the British Isles, and at what stage of its development it does so, are key to its impact on UK weather – in general the closer the ‘bomb’ tracks to the British Isles the more severe the weather.





Max UK wind speeds – 10 December 2014

10 12 2014

UPDATED AT 11:30AM ON 10th DECEMBER 2014

Parts of the UK are being affected by strong winds today – particularly the north-western coast of Scotland.

Winds are generally much lighter in south-eastern parts, although still gusty – particularly around coasts.

We’ll be updating this post through the day with the maximum wind speeds (from non-mountain sites) seen so far.

Date and time Station Area Speed (mph)
10/12/2014 10:00 TIREE ARGYLL 81
10/12/2014 09:00 SOUTH UIST RANGE WESTERN ISLES 79
10/12/2014 05:00 ISLAY: PORT ELLEN ARGYLL 77
10/12/2014 03:00 MACHRIHANISH ARGYLL 73
10/12/2014 06:00 LOCH GLASCARNOCH ROSS & CROMARTY 70
09/12/2014 22:00 HIGH BRADFIELD SOUTH YORKSHIRE 70
10/12/2014 10:00 KIRKWALL ORKNEY 69
09/12/2014 22:00 WIGHT: NEEDLES OLD BATTERY ISLE OF WIGHT 69
10/12/2014 06:00 SULE SKERRY ORKNEY 69
10/12/2014 06:00 STORNOWAY AIRPORT WESTERN ISLES 69

Winds are almost always stronger at our high level weather stations (those that are sited at 500 metres of altitude or higher), which are also often very exposed.  For this reason the winds from those sites are unlikely to reflect what the vast majority of people are experiencing. Bearing that in mind, the strongest gusts from the high level sites are quoted below for reference:

Date and time Station Area Height (metres) Speed (mph)
10/12/2014 11:00 CAIRNGORM SUMMIT INVERNESS-SHIRE 1237 109
10/12/2014 05:00 BEALACH NA BA NO 2 ROSS & CROMARTY 773 105
10/12/2014 04:00 AONACH MOR INVERNESS-SHIRE 1130 98
10/12/2014 06:00 CAIRNWELL ABERDEENSHIRE 928 94
10/12/2014 03:00 GREAT DUN FELL NO 2 CUMBRIA 847 82




Untangling the global drivers of UK winter weather

25 11 2014

As we head towards the start of winter, which starts for meteorologists on 1 December, there’s always a great deal of media and public speculation about what weather we might have in store.

To answer that question, we need to look beyond the UK. The worlds’ weather is interconnected, and there are certain large scale global drivers which we know have influences on UK weather at this time of year – so what are these doing at the moment?

El Niño, which sees unusually warm sea surface temperatures across the tropical Pacific and can increase the risk of cold winter conditions in the UK, has been much discussed after initial signs of development earlier this year.

Its progress has been slow, however, and while there remains a good chance of a weak event by the end of the year it is also possible that El Niño conditions will remain neutral. In any case, this factor is not expected to be strong enough to exert much influence on weather patterns in Europe during the next three months.

The North Atlantic Oscillation (NAO) describes differences in the usual pressure patterns over the North Atlantic – with positive and negative phases.

A positive phase is thought more likely than a negative one on average over the next three months. This is characterised by enhancement of the westerly winds across the Atlantic which, during winter, brings above-average temperatures and rainfall to Western Europe.

As we head later into winter, confidence about the heightened likelihood of positive NAO reduces – suggesting chances of drier and colder conditions return closer to normal.

The Quasi-Biennial Oscillation (QBO) sees high level (stratospheric) winds over the equator change from westerly to easterly phases – and it’s currently in the latter of the two.

In winter months this can lead to a greater incidence of high pressure blocking patterns over the northern hemisphere, which would increase the probability of colder and drier weather across Europe. Essentially this is providing an opposite signal to the NAO.

There are other factors to consider too. For example, Arctic sea ice extent is slightly below average but as yet it is not clear whether this might have an impact on weather patterns in the UK.

No single one of these drivers will determine the UK’s winter on its own – instead they all interact together to govern the weather trends we can expect over the coming months.

Disentangling these different influences remains a challenging area of science which the Met Office is improving all the time, but detailed and highly certain UK outlooks are not possible over these timescales.

The Met Office’s long-range outlooks give probabilities based on scenarios of being considerably wetter or drier, colder or milder than usual.

Currently the outlook for December 2014 to February 2015 suggests that milder and wetter than average winter conditions are slightly more likely than other outcomes. However, compared to day-to-day weather forecasts, the probabilities are much more finely balanced – for example, the outlook gives a 1 in 4 chance of the mildest scenario and a 1 in 10 chance of the coldest scenario. These numbers suggest it would be a mistake to interpret the outlook for a very mild outcome as ‘highly likely’; likewise very cold conditions cannot be ruled out.

The outlook gives similar probabilities for precipitation (rain, hail, sleet and snow), with the chances of the wettest scenario being 1 in 4 and the chances of the driest around 1 in 10.

These three month outlooks cover a whole three month period, taking into account both day and night, as well as the whole of the UK. This means that even in the event of, say, an overall mild winter we could still see spells of cold or very cold weather.

With this in mind, what exactly we’ll see for the winter ahead remains uncertain. In terms of strong winds, heavy rainfall, cold snaps or even snow, while longer-range outlooks can give us general tendencies, the details can only be predicted by our day-to-day weather forecasts.

The Met Office’s accuracy over all timescales is world-leading, however, so you can trust that we’ll keep everyone up-to-date with all the latest information on the weather whatever the winter has in store.





US snowfall and will it impact the UK?

20 11 2014

Parts of the US and Canada are seeing particularly cold weather and heavy snowfall at the moment.

Chart showing the position of the jet stream over North America as at 00:01 on 20 November.

Chart showing the position of the jet stream over North America as at 00:01 on 20 November.

A southward buckle in the jet stream has seen cold polar air flow south to north eastern parts of North America.

In the Buffalo region of New York state, temperatures have fallen as low as -15C and 4-5 ft (about 1.5 metres) of snow has fallen – enhanced by what’s known as the ‘lake effect’. Another 2-4 ft (about 1 metre) is expected through today.

The snowfall is set to ease on Friday with much milder conditions through the weekend giving a rapid and significant thaw – which could bring a risk of flooding.

This risk could increase through the start of next week when some very heavy rain is expected across the area.

What is lake effect 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

This is an effect which applies to areas around large lakes like those seen in the northern US – Lake Superior has an area of more than 30,000 sq miles.

When cold air moves across the relatively warm waters of the lake, air rises due to convection which creates clouds and heavy showers. In cold conditions, the moisture in the clouds will fall as heavy snow.

As Buffalo as it the eastern tip of Lake Erie it has been particularly susceptible to this effect during the recent weather.

While we don’t have any lakes big enough for this effect in the UK, we can occasionally see a similar scenario when we get easterly winds in the winter.

Cold air from the continent can be warmed by the relatively warm North Sea as it moves across the water, bringing snow showers to eastern parts of the UK. However, there’s no sign of this in the immediate future for the UK.

Will the US weather affect the UK?

Many people believe that there’s a rule of thumb that weather in the US will arrive in the UK a few days later – but that’s by no means always the case.

In this instance, there’s high confidence that the cold snowy weather will stay on the western side of the Atlantic.

Also, in past winters similar weather situations in the US have strengthened the jet stream and increased the risk of storms across our shores. Again, in this instance, this isn’t expected at the moment.

What we do expect to see is further changeable weather over the coming few days.





Top UK wind speeds as Gonzalo’s remnants felt

21 10 2014

TABLE UPDATED AT 11:50AM

Many parts of the UK are seeing strong winds today as the remnants of ex-tropical storm Gonzalo pass over the north of the country.

Below are the top ten strongest gusts of wind we have recorded so far today. We’ll be updating this through the day with the latest information.

Time Station Area Elevation Max gust (MPH)
0600AM WIGHT: NEEDLES OLD BATTERY ISLE OF WIGHT 80 70
0300AM ABERDARON GWYNEDD 95 70
1000AM ST BEES HEAD CUMBRIA 124 69
0400AM MUMBLES HEAD WEST GLAMORGAN 43 67
1000AM ISLAY: PORT ELLEN ARGYLL 17 66
0300AM CAPEL CURIG GWYNEDD 216 66
1000AM EMLEY MOOR WEST YORKS 267 66
0400AM LAKE VYRNWY POWYS 360 63
0600AM SALSBURGH LANARKSHIRE 277 63
0400AM MACHRIHANISH ARGYLL 10 62

The Met Office has issued a severe weather warning for the winds today – you can see the details of this on our warnings pages.

Winds are expected to be strong through much of the day, and people are advised that there may be some traffic and travel disruption.

Rainfall

Ex-Gonzalo also brought a band of heavy rain across the UK earlier this morning, bringing some notable rainfall totals in places.

The table below shows the top ten UK rainfall totals recorded between 1am and 8am this morning.

Station Area Total (mm)
CLUANIE INN NO 3 ROSS & CROMARTY 38.0
CAPEL CURIG NO 3 GWYNEDD 34.4
ACHNAGART ROSS & CROMARTY 30.6
TYNDRUM NO 3 PERTHSHIRE 27.6
KINLOCHEWE ROSS & CROMARTY 25.8
RESALLACH SUTHERLAND 23.4
SHAP CUMBRIA 21.8
LOCH GLASCARNOCH ROSS & CROMARTY 21.8
MORECAMBE NO 2 LANCASHIRE 20.2
LEVENS HALL CUMBRIA 20.0




Windy weather on the way

19 10 2014

As forecast, Hurricane Gonzalo made landfall over Bermuda on Friday with rain and winds of up to 110 mph causing power cuts, flooding, felled trees and damaged buildings.

The storm has continued in its journey since then, and passed the Canadian island of Newfoundland during Sunday morning.

The remnants of this tropical storm are being caught up in the westerly flow across the Atlantic and will be drawn towards the UK, crossing the country on Monday night and early Tuesday.

By the time Gonzalo crosses the Atlantic, however, it will be a very different system to the hurricane that affected Bermuda.

It will undergo what meteorologists call ‘extra-tropical transition’, which means it loses the warm-core typical of a tropical cyclone and becomes a much more standard Atlantic low pressure system – like we regularly see around the UK at this time of year.

As such the low pressure is expected to produce wind strengths and rainfall amounts which are not unusual over the British Isles during the autumn and winter months.

Whilst there is good confidence that this system will cross the UK on Monday night and Tuesday morning, there is still something to play for in pinning down the exact location of the strongest winds.

The Met Office has issued a weather warning for wind for much of the UK for Tuesday, particularly since the strongest winds look to coincide with rush hour for some locations, leading to possible travel disruption.

You  can see details of what to expect in the warnings page on our website. You can stay up to date with all the latest for the windy weather and what to expect for the rest of the week with our forecasts and warnings.








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