Weather news

Severe weather and La Niña latest

The latest La Niña event in the tropical Pacific Ocean continues to have a significant impact on weather conditions in various regions around the world. The latest update from the WMO predicts that the current episode will last for at least the first quarter of 2011, and possibly towards the middle of the year, after which its lifecycle becomes more uncertain.

Since this near-record La Niña began, severe flooding has been experienced as very heavy rain and landslides affected regions of Australia, southern Africa, Brazil and Sri Lanka, amongst others. La Niña cannot be directly linked to all of these events, with some more likely a result of the underlying variability in global weather. However, there is a strong correlation between the colder-than-average ocean waters in the central and eastern tropical Pacific and severe weather affecting parts of Indonesia and northeastern Australia, in particular. Ocean temperatures in this region have averaged 1.5 degC below normal, leading to a marked ocean-atmospheric cooling. This in turn leads to reduced cloudiness and stronger trade winds. In addition, anomalously low sea-level pressure and above average sea-surface temperatures in the western tropical Pacific and eastern Indian Ocean have led to very high rainfall in the affected parts of Australasia. Indeed, the period July to December was Australia's wettest on record.

This news came as Australia experienced what was described by some as the worst storm in memory to hit the state of Queensland. Strongest winds were estimated to be in the region of 190mph as Category 5 Cyclone Yasi made landfall near the town of Tully just south of Cairns. Fortunately, the storm's path was well forecast and the population was prepared for the worst. There was significant damage to infrastructure and buildings, especially along the coast, but residents had boarded up houses and evacuated hospitals in readiness. Yasi continued its path across northeastern Australia as it weakened, but remained a marked depression.

Elsewhere in the world, torrential rain in Brazil had more devastating consequences for human life as over 800 people were killed and thousands made homeless in severe flooding and massive landslides. The mountainous area of Serrana to the north of Rio de Janeiro was the worst hit. Thousands more were trapped in their homes and temporary hospitals were set up by the military. The area is a relatively wealthy one, but construction policies were criticised for allowing houses to be built in allegedly unstable locations. Aid arrived from all over the world, with the Brazilian government promising to build thousands of new houses for those made homeless.

The BBC ‘Weather Test’

BBC News and BBC Radio 4's Today programme are running a project to study weather forecasts from a number of different forecast providers in order to attempt to determine which organisation is the most accurate. The project's steering group includes representatives from such institutions as the Royal Meteorological Society, the Royal Statistical Society and the Royal Astronomical Society, with Leeds University providing the results of the comparison.

The organisers recognise that this is a serious and complex undertaking, with countless parameters to consider and the potential for an enormous amount of data. Judging the accuracy of a forecast is a minefield with no definitive method for measuring overall precision. Forecast accuracy is traditionally highly dependent on the audience at which is it aimed, with, for example, a member of the public organising a barbecue having a quite different perception of accuracy from an energy provider planning electricity demand.

Much is still to be decided, with the steering group's initial meeting asking more questions than there were answers. They are quite realistic that the project may fail to provide an overall answer. The methodology of the project remains to be agreed with everything to be decided from the forecast locations and parameters to the forecast timescales. However, the BBC hopes that forecast providers will be keen to take part in order to prove their abilities in an independently-judged forum.

More information is available from the Today programme's website:

Very wet northeast monsoon in Kerala

The period October to December is known as the northeast monsoon season in Kerala, southwest India, and normally contributes about 16% of the annual rainfall for the region. Since 1901, the wettest such season was in 1932, when 835mm of rain fell, and the driest was 1988 with 180mm: the average rainfall is 499mm.

In 2010, 826mm was recorded, causing havoc for farmers in Tamilnadu, South Kerala and coastal Andhra Pradesh with the loss of paddy and other agricultural crops, whilst, of the eight districts in South Kerala, five (Thiruvananthapuram, Pathanamthitta, Kottayam, Alleppey and Ernakulam) reported their highest ever northeast-monsoon rainfall. The worst single incident came when a depression crossed the south Andhra coast on 8 December. Following its intense rainfall, a landslide disrupted rail services on the Trivandrum to Nagercoil line for about a week. (Information supplied by R. Lakshminarayanan).

2010: a record year

Despite the severe winter experienced across many northwestern parts of Europe, last year ranked as the joint warmest on record globally, according to data published by the WMO. They describe the average global temperature as showing no statistically significant difference between temperatures recorded in 2010, 2005 and 1998. 2010's global average temperature was 0.53 degC above the long-term average.

The WMO derives these statistics from data sets managed by the Met Office Hadley Centre, the US National Climatic Data Center and NASA (the US National Aeronautics and Space Administration).