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.


Heavy rainfall and floods in India and Pakistan

10 09 2014

Heavy rainfall has devastated parts of India and Pakistan in recent days, leading to some of the worst flooding in decades.

The extreme conditions were caused by a tropical depression associated with the ongoing monsoon season which tracked northwards across the countries, bringing exceptional rainfall totals over short time periods.

In the Punjab province of Pakistan, some areas saw around 300mm (12 inches) of rain falling in less than 24 hours. This is close to the amount of rainfall we would expect through the whole of the winter in the UK.

Although the heaviest of the rain has now eased, water levels in some parts of the countries are continuing to rise.

Hundreds of people are thought to have died as a result of the floods, with officials saying that around 400,000 people are stranded in Indian-administered Kashmir. Around 700,000 people have also been told to leave their homes in Pakistan due to rising water levels.

Further hurricanes expected in west Atlantic

9 09 2012

The Met Office has been closely monitoring Tropical Storm Leslie during the past week, especially because of the possibility of the impact on Bermuda. It now looks like Leslie will strengthen to Hurricane Force as it tracks 100-150 miles east of Bermuda late on Sunday. Therefore, although around 100 mm of rain and gale force winds are expected, no significant impact is expected across Bermuda, although dangerous rip currents are predicted by the US National Hurricane Centre.

This graphic shows the position and forecats track tropical storm Leslie. The orange circle indicates the current position of the center of the tropical cyclone. The black line and dots show the National Hurricane Center (NHC) forecast track of the center at the times indicated. The dot indicating the forecast center location will be black if the cyclone is forecast to be tropical and will be white with a black outline if the cyclone is forecast to be extratropical. If only an L is displayed, then the system is forecast to be a remnant low.

This graphic shows the position and forecast track tropical storm Leslie. The orange circle indicates the current position of the center of the tropical cyclone. The black line and dots show the National Hurricane Center (NHC) forecast track of the center at the times indicated. The dot indicating the forecast center location will be black if the cyclone is forecast to be tropical and will be white with a black outline if the cyclone is forecast to be extratropical.

All available forecasts track Hurricane Leslie, and Hurricane Michael, which is situated to the east, quickly north through Monday and Tuesday.

Meanwhile, an active cold front which was responsible for the rare New York tornadoes and the high profile disruption to the US Tennis Open Championships will continue to move east from the eastern seaboard of North America.

Hurricanes Leslie and Michael and this cold front are expected to converge east of Nova Scotia and south of Newfoundland bringing the risk of 100-200 mm of rainfall to the area through Monday and Tuesday.

Probabilities of surface wind speeds exceeding 58 mph

Probabilities of surface wind speeds exceeding 58 mph from US National Hurricane Centre

However the main risk remains to the marine community with wind speeds in excess of 65 knots from late Monday to early Wednesday. Combined with eight metre waves and potentially a maximum wave height of up to 16 metres there will be hazardous sea conditions across the Grand Banks fishing grounds which is the same area as was impacted by the ‘Perfect Storm’ in the Autumn of 1991.

Beyond this, the remnants of this combined storm may swing east and push across the Atlantic, influencing the weather over the north east Atlantic toward the end of the week. Currently the area of low pressure is expected to push well to the north of the UK, but will potentially push a frontal south across the UK bringing rain and gale force winds to the north on Thursday and Friday. However there is still a good deal to play for in the forecast for the end of the week and you should keep up to date with the latest weather forecasts and warnings on the Met Office website.

Pakistan Monsoon brings exceptionally heavy rain.

Elsewhere, the Pakistan Monsoon has brought some exceptionally heavy rain to the region. Khanpur, on or close to the Indus River in Pakistan reported 147mm of rainfall in just 12 hours up to midnight last night UK time. Such heavy and intense rainfall associated with the Indian Monsoon is likely to bring significant and rapid localised flooding issues to this area in the coming days. 

Across Sindh and Punjab provinces over the last 72 hours stations have been reporting varying 12-hourly totals with anything between 10 and 60 mm at times.  

Forecasts indicate that rain is expected to continue for another 48-72 hours, with peak intensity over next one to two days. So the situation could worsen initially before events begin to ease off slowly during the early part of next week.

Monsoon rains bring devastating floods to southern Pakistan

14 09 2011

Parts of Pakistan and Thailand have seen devastating floods after two weeks of persistent torrential rain. The floods have come at a time when many parts of South Asia expect heavy rainfall as part of the region’s summer monsoon, but it has been particularly heavy for the affected areas and it has come late in the season.

It is usual for monsoon rainfall to vary from year-to-year and for there to be large regional differences in the amount of rain, but what has caused the problems this year?

Observations show there has been a series of low pressure systems passing over Pakistan from northern India over the past two weeks, with little respite in between. This has given no time for water to flow away or seep into the ground, causing a build up of floodwater.

With the rain coming so late in the season, there are indications that the region’s monsoon is continuing beyond its usual length. This means the conditions which persist in a monsoon and bring the heavy rainfall have allowed the low pressure systems to continue to move over the region, bringing the heavy rains with them. It’s not clear why the monsoon would be extended like this, but there is some suggestion that this may be related to knock-on effects from long-term cycles in sea-surface temperatures in the Pacific and Indian Oceans, although it could also be part of the normal year to year variability in the length of the monsoon period.

In 2010, while the flooding was similarly devastating, the reasons behind it were different. This came in the middle of the monsoon season and most of the heaviest rainfall came from a single low pressure system which moved over the region over a period of four or five days. Such low pressure systems aren’t unusual, but in this case it was unusually intense and moved very far to the west – causing the floods. The low pressure system was intense because atmospheric conditions prevailing at the time meant the low pressure dragged in additional warm moist air from the Indian Ocean, intensifying the rains.

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.

Met Office on Newsnight

23 08 2010

On BBC Two tonight, Newsnight Science Editor Susan Watts will be examining claims by senior climate scientists that global warming is a “major contributing factor” (Dr Ghassem Asrar, director of the World Climate Research Program). As part of this Susan will be asking Met Office Chief Scientist, Prof Julia Slingo what role, if any, climate change has played in this disaster, whilst our forecasters at the BBC Weather Centre explain more behind the science of the monsoon and the developing La Nina.

Pakistan floods – More than just an active monsoon?

23 08 2010

As the severe flooding in Pakistan appears to worsen once again our Chief Scientist, Professor Julia Slingo, investigates why there has been such severe floods in Pakistan.

Pakistan typically receives about half its annual rainfall of 250–500 mm during July and August so reports of 24-hour totals in excess of 300 mm on 29 July particularly in the head waters of the Indus River were exceptional.

Simply saying that this was part of an active Indian Monsoon season cannot alone explain the exceptional nature of the rainfall. Most summers see active spells of the Indian Monsoon where the rains spread north and west into Rajasthan, the Punjab and Pakistan. But what happened this month appears to be much more than where an active spell of the monsoon interacted with a very disturbed pattern of weather from the mid-latitudes.

Usually during the summer, the airflow high in the atmosphere (the troposphere) over northern India, the Himalayas and Pakistan, is dominated by the monsoon anticyclone which pushes the sub-tropical jet stream to the north of the Tibetan Plateau. This prevents weather systems from reaching very far south. 2010, however, was different with the upper level airflow over the whole of Asia being very disturbed.

The results of this were record-breaking high temperatures in Moscow leading to fatalities, forest fires and damaged crops. On July 29 the temperature soared to 38.2 °C (the average high being 20 °C). That, according to Russian meteorologists is a once in a thousand year event. That same pattern affected Pakistan, with a deep trough forming downstream of the anticyclone over western Russia.

Another consequence of this disturbed weather pattern was the excessive rainfall over China, causing major mudslides and the Three Gorges Dam to almost reach its capacity of 185 m.

Pakistan floods
In Pakistan on 28/29 July this trough moved to the east and south down into northern parts of the country. The colder, unstable air aloft interacted with the warm moist air from the Indian monsoon to the south, which activated a line of intense storms along the mountains of Pakistan, feeding into the Indus River. A similar situation developed on 3 August leading to further heavy rain that hampered relief efforts.

So, it would seem that Pakistan floods were the result of a conjunction of an active Indian monsoon with an unusual weather pattern that occurred just over the mountains of western Pakistan and fed vast amounts of rainfall into the head waters of the Indus River.

Were other factors involved?

La Niña
The whole Asian Summer Monsoon system was very active and this could be attributed, in part, to the La Niña developing in the equatorial Pacific Ocean since the early summer. La Niña is the opposite phase of El Niño and is characterised by cooler than normal ocean temperatures in the central and East Pacific. The effect of this is to contain the warmest waters in the western Pacific which then drives a stronger than normal monsoon. Weather patterns circle the globe and it is possible that the disturbed nature of the pattern in August 2010 was driven by the strong monsoon — this is a process known as teleconnection.

Climate change
Another reasonable question to ask is whether global warming had any part in this extreme weather. It’s very hard to attribute any particular extreme event to climate change and, as in all cases, there is a plausible explanation for the natural variabilty of our weather and climate.

However, there is evidence from observations, especially in India and China, that periods of heavy rain are getting heavier. This is entirely consistent with our understanding of the physics of the atmosphere in which warmer air holds more moisture. Our climate change predictions support this emerging trend in observations and show a clear intensification of extreme rainfall events in a warmer world.

So, although climate change is very unlikely to have been solely responsible for the recent extreme weather, it is likely that climate change is loading the dice and shortening the odds of heatwaves and heavy rainfall events around the globe.

Met Office in the Media: 16 August 2010

16 08 2010

The weekend papers continue to report on the extreme weather being experienced across the world, and the reasons behind such weather.  The Observer focused on scientists meeting in Colorado this week to explore operational attribution of climate related extreme weather.  This follows Dr. Peter Stott writing in The Guardian earlier last week. Climate change: how to play our hand, explored the fact that there have always been extremes of weather around the world but evidence now suggests human influence is changing the odds.

In Tom Chivers latest Blog for The Telegraph, Climate change, Pakistani floods and causality, he focuses on the causes of the Pakistani floods. In his article he expands Dr. Peter Stotts ‘loaded dice’ analogy which explains the idea that climate change has now made the types of extreme weather such as the Pakistani floods and Russian heatwave more likely to occur.


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