Record levels of Pacific tropical cyclone activity continue

13 07 2015

The Pacific Ocean has seen an extremely high number of tropical cyclones during the early part of this season, with several more tropical storms developing over the weekend.

Across the whole Pacific Ocean nine tropical cyclones have formed in the last two weeks. The recent high level of activity is a response to the recent strong episode of the Madden-Julian Oscillation combined with the developing El Niño conditions as described in our previous blog.

Several of the recent tropical cyclones have formed over open ocean and have caused little or no disruption. However, others have either affected land areas or are set to do so this week.

Typhoon Chan-hom passed very close to the coast of China at the weekend, with over a million people having to be evacuated from the Shanghai region. Whilst coastal areas saw heavy rain and powerful waves, they were spared the strongest winds as the eye of the typhoon stayed offshore. Chan-hom brought heavy rain to North Korea with 400mm having been recorded at Kimchaek on the northeast coast.

Typhoon Nangka on 13 July 2015. Image courtesy of The National Institute of Informatics

Typhoon Nangka on 13 July 2015.
Image courtesy of The National Institute of Informatics

Typhoon Nangka has just turned northwards in the west Pacific and looks set for landfall over south-western Japan on Thursday bringing the risk of strong winds, heavy rain and storm surge.

Across the other side of the Pacific, Tropical Storm Dolores looks set to become a hurricane as it runs parallel to the Mexican coast. It is most likely to stay out at sea, but there remains a low possibility that it could turn towards the coast in a few days time.

Pacific records

The recent high levels of tropical cyclone activity have resulted in some remarkable statistics.

  • Seven tropical cyclones (including four major typhoons) occurred in the western North Pacific before the end of May beating previous records.
  • The three tropical cyclones which have formed in the central North Pacific this week formed earlier in the season than any previous tropical cyclone in this region. There have never been three storms form in such quick succession in this region.
  • Eight tropical cyclones have formed across the eastern and central North Pacific so far this year – the earliest in the season this has ever occurred.
  • Across the whole North Pacific there have been 19 tropical cyclones so far this year. Taking into account their strength and longevity this amounts to a record 321% of normal activity for this point in the season.

Atlantic calm

By contrast the Atlantic remains very quiet. Two short-lived tropical storms have formed so far (Ana and Bill), but conditions are not conducive for further development in the near future in the tropical Atlantic:

  • Sea surface temperatures in tropical areas are up to 2°C below normal values
  • Wind shear (which inhibits tropical cyclone development) has been persistently high for several weeks.
  • Sea level pressure has been at record high values in the last month.

The growing El Niño is likely to maintain conditions which suppress tropical cyclone activity in the tropical Atlantic for the foreseeable future. However, some tropical cyclone activity cannot be ruled out – particularly outside of the tropics at higher latitudes where conditions are not as harsh as those described above.

Further Information

Official warnings for the latest tropical cyclones are produced by the Japan Meteorological Agency, the Central Pacific Hurricane Center and the 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 on StormTracker and via @metofficestorms on Twitter.

Met Office continues to drive forward research on long-range forecasting

29 03 2013

The BBC Radio 4 ‘Today’ Programme have run a story this morning regarding the advice the Met Office gave to our government customers ahead of the exceptionally wet weather of April to June 2012.

This was an extreme period of weather that saw a marked change from dry conditions to very wet conditions in a very short period of time.

Following the exceptionally wet weather of late spring 2012 the Met Office provided a full report into the possible reasons for the switch from dry to wet conditions. Our report states that the advice provided in the long-range outlook for April to June 2012 issued in March 2012 ‘was not helpful’ to our government customers.

However, looking at the skill of these outlooks over many individual forecasts clearly shows that they provide useful advice to their specialist users on over 65% of occasions. In addition these outlooks are never used in isolation but form one part of a range of forecasts from the Met Office including regular monthly outlooks and highly accurate 1 to 5 day forecasts and warnings.

Facing up to the challenge of long-range forecasting

The science of long-range forecasting is at the cutting edge of meteorology and the Met Office is leading the way in this research area. We are continuing to work hard to develop the science of long-range forecasting. We are confident that long-range outlooks will improve progressively and that the successes we have achieved in other parts of the world already will, in the future be mirrored in the UK.

The Met Office constantly reviews the accuracy of our forecasts across all time scales and is recognised by the World Meteorological Organization as one of the top two national weather forecasting services in the world. We also routinely verify our short-range forecasts on our website.

The ‘big switch’ of April 2012

During March 2012 the La Nina event that had persisted from 2009 was finally waning in the Pacific (as predicted by the seasonal forecast system), although many parts of the global oceans and tropical weather patterns still retained characteristics associated with La Nina. In the northern hemisphere the jet stream was very disturbed, resulting in a wave pattern of high and low pressure regions. The UK was positioned under a strong high pressure region resulting in very dry and warm conditions. In April, the wave pattern underwent a significant shift to bring the UK under the influence of strong low pressure, with prevailing south-westerly flow and heavy rainfall.

As detailed on ‘Today’, one of the potential causes of this shift in the northern hemisphere circulation may have been associated with a shift in tropical weather patterns. In particular, this may have been caused by a strong Madden Julian Oscillation (MJO) which occurred in March. This is a large-scale tropical phenomenon which leads to disturbed weather patterns over a timescales of typically 30-60 days. This changes originating over the Indian Ocean may have influenced our northern hemisphere weather regimes. Understanding the initiation of an MJO event is, however, largely unpredictable, and remains one of the great unsolved challenges of tropical meteorology.

Due to the fact that the initiation of an MJO is largely unpredictable – combined with knowledge that often subtle, and sometimes small, shifts in hemispheric circulation patterns can make all the difference between fine, dry weather and unsettled, wet weather over the UK – it is very unlikely that its impacts could have been anticipated in any forecasts for the coming months issued in early and mid-March.

A complicated world

Finally, although one reason for the switch in the fortunes of our weather in 2012 may have been the MJO, there are other parts of the climate system which we increasingly recognise as having an influence on our weather patterns. These include the North Atlantic Ocean temperatures, solar variability, the circulation of the upper atmosphere – the stratosphere – and of increasing interest, the changing state of the Arctic.

Better understanding and representing the drivers of predictability in the global climate system that influence our weather patterns is as ever a priority for Met Office research in order to deliver improved advice and services on all timescales.


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