BioEd Online

US government scientists have released their latest prediction for how many hurricanes to expect in the Atlantic Ocean this summer. And the forecast contains a stark warning: don't let the relative calm of last year lull you into a false sense of security.

"For 2007, we're predicting a high probability of an above-average hurricane season," says Gerry Bell, lead hurricane forecaster at the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center in Camp Springs, Maryland.

His team predicts that there will be 13 to 17 named tropical storms in the Atlantic this year. Of those, seven to ten will become hurricanes — and as many as five could become 'major' hurricanes, with winds of 178 kilometres per hour or greater.

The numbers are roughly similar to the predictions produced for 2006. But that forecast was too severe: fewer hurricanes than expected materialized (see 'How the NOAA forecast fared last year'). This was thanks to a sudden and late surge by El Niño — the rise in temperatures in the tropical Pacific that can also affect weather patterns in the Atlantic, thus suppressing hurricanes.

This year, however, forecasters expect El Niño to be followed in the next one to three months by its counterpart La Niña, which features cooling of tropical Pacific waters that can encourage the formation of Atlantic hurricanes. This means that the forecasts are unlikely to fall short a second time.

Perfect conditions

In 2005, a record number of Atlantic hurricanes pounded the United States and the Caribbean, including the devastating Katrina. And the incidence of hurricanes has been higher since the mid-1990s than it was for several decades prior to that. Nine of the past 12 seasons have had above-average activity.

Since 1995, wind and water conditions off the western coast of Africa, where Atlantic hurricanes form, have been just right for tropical storms to be born, Bell explains. Ocean temperatures along their path have been higher than normal, providing more energy for growing storms to feed on.

The NOAA forecast for this year is strikingly similar to that produced by another leading hurricane-forecasting team. In April, researchers at Colorado State University in Fort Collins predicted 17 named storms, with nine hurricanes and five major hurricanes.

Be prepared

More than half of the US population lives in coastal areas, and NOAA uses its annual hurricane forecast to emphasize how residents should ensure that they have the right emergency equipment. "It is a big mistake to count on being lucky," says Michael Chertoff, secretary of the Department of Homeland Security and the man who came under much fire for the lacklustre federal response to the Katrina disaster in 2005.

NOAA's news briefing on 22 May carried an undercurrent of tension, as vice-admiral Conrad Lautenbacher, the agency's head, shared the stage with the director of the National Hurricane Center in Miami, Bill Proenza. Late last week, Proenza accused NOAA of spending too much money on public outreach efforts and not enough on hurricane forecasting. Lautenbacher retorted on 21 May that he would provide whatever money is necessary to keep the hurricane centre operating at the level it needs.

As part of recent developments, this year the hurricane centre will be using a new computer modelling system to track storms as they develop. Called the Hurricane Weather and Research Forecast system (HWRF), it has been tested alongside the traditional forecasting models for the past three seasons, says the project's leader Naomi Surgi.

The new model incorporates several improvements, such as adding in real-time Doppler radar data gathered by the 'hurricane hunter' jets that fly into the hearts of storms. "It's been doing great," says Surgi. On 18 June, HWRF will become the main model that the hurricane centre will use to track storms. The old model will run in parallel so that forecasters can track which one performs better.

NOAA plans to update its forecast in August, just as peak hurricane season hits.