Tuesday, March 31, 2009

Rain, hail or shine in Dubai nowadays

The country has been witnessing rough and unstable weather conditions since last week with all the emirates witnessing showers and thunderstorms.

Emirates such as Fujairah and Al Ain have been one among the worst affected with the weather conditions rendering people homeless too.

On Monday, the capital and other emirates including Dubai witnessed moderate to heavy rainfall in the afternoon. Rains continued till late evening in the capital causing traffic snarls in many places in Abu Dhabi and Dubai.

The Met department in the capital has predicted more rains and thunderstorms during the night and today (Tuesday) morning in different parts of the country.

The unstable weather conditions have been caused due to upper air mass and low pressure in the atmosphere associated with cold air and moisture coming from the Indian Ocean, the centre said.

Forecasting rain, hail or shine

Clive Stevens

  • Last Updated: March 28. 2009 8:30AM UAE / March 28. 2009 4:30AM GMT

Sitting in the transit lounge of Bahrain airport on my way back to Dubai, I overheard a conversation between two businessmen waiting for their flight. “Weather forecasting in this part of the world must be one of the easiest jobs going,” said one. “Hot and sunny with blue skies every day.”

Unable to resist, I leant forward and introduced myself. “I am that weatherman and it is definitely one of the best jobs in the world.” They were both somewhat taken aback.

As the past few days have shown, however, the job of the weather forecaster can have its moments. And this is a better time than most to offer an insight into how we weathermen of the UAE function, especially under pressure.

Stormy weather is not that unusual at this time of year but to have it forecast to extend over four or five days is. High winds and thunderstorms have been sweeping across the UAE, making conditions dangerous in places. On Thursday three labourers died when the roof was blown off the warehouse they were building and a wall collapsed on them. Crosswinds of more than 100kph have caused difficulties for planes coming in to land, trees have been uprooted, roads flooded and large hailstones have battered cars.

In fact, this has been a rather extreme year for UAE so far. In January, 10cm of snow fell on the Jebel Jais mountain of Ras al Khaimah and temperatures dropped well below zero. It was only the second time snow had been recorded there.

The following month temperatures reached 37°C, the highest for a February day since records began. And now we are cowering under stormy skies. Such extreme weather events, however, are not anything sinister and they are not necessarily proof of global warming. They are just random yet explicable fluctuations in weather patterns.

This is a particularly changeable time of year – the transition between winter and summer. March and April can be volatile. For example, temperatures were 37°C on Wednesday and 27°C on Thursday.

Southerly winds from the Empty Quarter bring hot weather but winds from the north are naturally cooler at this time of year. As the air near the surface heats up more quickly than the air at higher altitudes, the atmosphere will become unstable – in just the same way as a boiling kettle. The warm, humid air rises and meets the cold air, the moisture condenses to cloud and the result is thunderstorms and hail. That’s what has been happening over the past few days.

Having worked at the Dubai International Airport Met Office off and on for 30 years, I have lived through several extreme weather events.

On April 30 1980 a massive sandstorm raged all day. It had formed in the Empty Quarter and travelled towards the coast. During the early evening an extremely violent thunderstorm developed over the sea, sucking in all the energy around it. At around 8pm it came in from the sea and cut across Dubai. Surface wind speeds gusted to 120kph at the airport. The centre of the storm crossed the Dubai-to-Sharjah road near Al Mullah Plaza. Cars were blown over and rolled off the road into the desert under its force. Several hundred sheep corralled outside in open pens were reported killed by that hailstorm. It was a miracle that no person was killed.

In the late 1970s another memorable storm struck Dubai airport during the night. The next day we had a call from the harbourmaster at Port Rashid asking if we had received any reports of a tornado. We hadn’t, we told him. The reason he had asked, he said, was that an anemometer at the port had shown a wind-speed reading of 120 knots (in excess of 200kph) just before it disintegrated. More astonishingly was the fate of two 13m fully-loaded sea containers that had been left stacked by the perimeter fence.

The next morning the top one was lying on the other side of the fence. It appeared the wind had somehow lifted it up in the air and blown it over without damaging the fence. Now that looks like a tornado.

Fog is a year-round problem. Just over a year ago a blanket of thick fog formed on the highway between Abu Dhabi and Dubai during the early morning rush hour. In what became known as Fog Tuesday, four people were killed, 350 injured and 20 cars caught fire amid the mass of wreckage. I remember a similar crash in the late 70s, on the Dubai to Sharjah road, which in those days was two lanes each way with no central barrier. Cars were diving off the road to avoid the 140-car pile-up.

My pet theory is that fog is closely associated with the natural boundaries of the UAE. It forms along the coastal region when moist air from the sea is blown inland and cools over the desert under clear night skies. It provides a valuable source of water in an arid region and helps plants to survive and has so helped define the habitable areas.

I graduated in meteorology and physics from Reading University in southern England in 1971. One of our lecturers told us that it might appear odd to study the two subjects together but that it would not be a prudent move to study meteorology on its own. When we were coming to the end of the course we found out what he was getting at. Only one student out of our year managed to get an interview at the British Met Office – and he was already working there.

However, I soon landed a job in Jamaica forecasting for the government at Kingston International Airport.

When I started in Dubai in 1976, the airport had only five check-in desks compared to the three terminal buildings today. In those days the only instrument we had was a Stevenson screen, a white box with slats that acted as a mini weather station. It contained wet and dry thermometers, a barometer, an anemometer to measure wind speeds and a couple of other instruments.

Now we work in a modern office at Terminal One of Dubai International Airport behind banks of computers monitoring fantastically sophisticated instruments, displaying satellite pictures and rainfall on radar screens and running incredibly complex computer models. These models produce forecast charts for up to 10 days in advance and are reasonably reliable forecasts for five days ahead.

In the early days, we had time to take calls from the public. I remember one man ringing in to ask when will the rain would stop because he wanted to clean his bicycle. On another occasion a woman rang saying her daughter was getting married in six weeks and asking would it rain? I said we only did five-day forecasts. Unperturbed, she asked if I could give her a forecast for April 16 to April 21, the date of her daughter’s wedding. I had to tell her it didn’t work like that.

Now, calls from the public would be a distraction from our core responsibilities, although we do have a recorded forecast, which people can access by ringing 04 216 2218. They can also register for forecasts on our website for a fee. A lot of companies, organisations and government bodies do this.

Services to aviation make up about 95 per cent of our work, with Emirates Airlines being our biggest user. We provide compulsory documentation for departing aircraft. A terminal aerodrome forecast tells the pilot what weather conditions he will meet when he prepares to land – wind speed, visibility, cloud cover below 1,600m and whether there are thunderstorms in the area.

Pilots also need to know jet stream wind speeds because a head or tail wind can dramatically affect flight times and the amount of fuel used.

There is a vast array of sophisticated sensors around the airfield to provide incoming pilots with critical real-time information. In the past year, Dubai Met Office has obtained a wind profiler, which measures wind speeds and direction at various heights.

Another instrument profiles temperatures at different heights. Heat can reduce engine performance so the pilot of a heavily laden aircraft will need to know if a surface temperature of 20°C raises to 30°C at 200m as this could affect his ability to climb. The runway is also lined with visual range equipment so the pilot can know from how far he will be able to see the runway lighting.

In terms of the sophistication of its meteorolgical equipment, Dubai International Airport is probably one of the best in the world.

So although it may be blue skies and sunshine most days, the weathermen of Dubai do perform a vitally important job that combines practical science, sophisticated technology and a passion for the ever-changing mysteries of the weather. Through it we contribute to all your safety by helping ensure efficient air traffic services at Dubai International Airport.

Clive Stevens is a forecaster at the Dubai International Airport Met Office

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