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Last Updated: Tuesday, 21 August 2007, 11:47 GMT 12:47 UK
The science of tracking hurricanes
By Matt McGrath
BBC News

As Hurricane Dean powers its way across the Caribbean, there are concerns that it will pick up speed over the warmer waters of the Gulf of Mexico and turn into a Category Five hurricane - the most intense level of storm.

satellite image

So how do scientists predict where a hurricane will hit - and how intense it will be?

When hurricane forecasting started back in 1954, meteorologists could only give a one-day warning of an impending tropical storm. Thanks to satellites and computer modelling this has now improved to five days.

But while the range of technology deployed to monitor hurricanes is impressive, there are still considerable problems with forecasting the path and intensity of these storms.

'Complications'

The track of a storm is controlled by streams of wind in the Earth's atmosphere and by trade winds on the surface of the seas near the equator.

We rely on statistical techniques. Currently there are much higher resolution models that are able to show some skill in predicting tropical cyclone intensity
Julian Heming, Britain's Met Office

Ironically, the higher the wind speed, the easier it is to predict the path. Weaker winds often mean a hurricane develops a mind of its own.

So far, according to experts, Hurricane Dean is behaving itself in terms of track.

Scientists are confident that its path will continue on a fairly straight westerly track that will take it across Mexico's Yucatan peninsula and then move into the Bay of Campeche in the south-west Gulf of Mexico.

Sometimes, though, there are complications that can cause abrupt turns and changes in direction.

"We have to look at the broader environment for the steering of hurricanes," says Julian Heming, a tropical cyclones expert with Britain's Met Office.

"Sometimes we do have complications, whereby you do get interactions with other weather systems that pass it in the opposite direction from west to east at higher latitudes.

"When this happens, it is sometimes difficult to know exactly what interaction there will be between them. Sometimes they might pull the hurricane northwards and that might cause an abrupt turn, sometimes it might cause it to stall for a while, but with Dean we haven't had these complications," Mr Heming says.

'Cyclical changes'

When it comes to predicting the intensity of a hurricane, it is a lot more difficult. It is partly to do with fluctuations in the surface temperature of the ocean.

In the case of Dean, it is expected that the warmer waters of the Gulf of Mexico will increase its strength. But there are other factors, according to Mr Heming.

"At the moment, we rely on statistical techniques. Currently there are much higher resolution models that are able to show some skill in predicting tropical cyclone intensity," he says.

"But if you are using a global model such as we use at the Met Office, even though the resolution has increased in recent years, it is still not high enough to accurately predict the intensity of these cyclones.

"This is because the inner core of the cyclone is so small, and the changes in wind strength right from the centre right to the outskirts of the storm are so large.

"We also see cyclical changes in these cyclones quite often. You can get intensification at the core of the system, then the inner eye wall collapses, then an outer eye wall - which is slightly larger - takes over, and that has slightly lower wind strength. So you get these cyclical changes in the wind strength that are very difficult to predict," Mr Heming says.


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Met Office on hurricane's path



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