Where has all the wet weather come from?

Traffic navigates flood waters on 15th street in Abu Dhabi after heavy rains.

Sudden onslaughts of winter rain and storms are common features of the UAE's sometimes highly changeable weather patterns, according to the National Centre of Meteorology and Seismology. In the summer, hot and sunny weather is generally maintained for months on end by the tropical jet stream, which brings warm air and high pressure from the east. But as temperatures fall in the winter, the subtropical jet stream moves further south, pulling wilder conditions in from the east.

In December, winds in the upper part of the atmosphere strengthen, allowing low pressure systems to migrate from the north and west. That can bring sudden rain showers and thunderstorms any time between December and March. Historically, March has recorded the most unpredictable and wet weather, with an average of six days of rain per year. By comparison, December usually sees just four days, according to the Dubai Meteorological Office at the city's International Airport.

The weather system that has caused sandstorms, clouds and precipitation over the past week was formed when a pocket of low pressure developed over the Red Sea. As the warm pocket of air rose and travelled east towards Abu Dhabi, it hit a shelf of cold air from the north-west in the upper atmosphere. When the two met, they formed the cumulus and cumulonimbus thunderclouds. The cloud bank is expected to pass today, although some isolated showers may be seen this morning, particularly in the northern and eastern emirates.

A spokesman for the NCMS said the clouds, winds and rain would also push temperatures down to 21°C. The shelf of cold air pushing the cloud bank east will become a problem by midweek, as winds reaching 20 knots are expected to cause sea swells of up to two metres. According to Dubai's weather office, January, February and March tend to be the wettest months of the year, with an average of 25mm of rain in February, against 15.1mm in December.

A spokesman for the Dubai International Airport meteorological office said that while winter storms were typical, it was difficult to compare this year's rainfall with previous years. "Sometimes we'll have no rainfall at all in a year and sometimes we'll get 150mm in one day," he said. "Nothing's really normal." @Email:[e-mail]