Hurricane Intensity Still Stymies Forecasters

(April 6) -- With a potentially dangerous 2010 hurricane season starting in a couple of months, meteorologists' ability to accurately forecast the storms is of the utmost importance. National Hurricane Center predictions related to the path of these storms continues to improve, but the government agency's forecasts of how strong they will be have not, posing a potential risk to residents in coastal communities.

A recent Houston Chronicle article notes that forecasts of the track of storm locations (for one-day, two-day and three-day periods) established records for accuracy during the 2009 hurricane season. The average error for a three-day forecast was 125 miles, which is a 50 percent improvement over the past decade. The forecasts for the intensity of the storm, whether strengthening or weakening, have not improved over the past two decades, however. The average intensity error last year was 21 mph, compared to 20 mph in 1990.

In response to the need for more accurate forecasts, the National Oceanic and Atmospheric Administration started the Hurricane Forecast Improvement Project a couple of years ago. The project's goals include continuing to improve the intensity forecast as well as the track forecast by 50 percent within 10 years.

Without an accurate intensity forecast, a storm near the coast that rapidly intensifies into a major hurricane and moves inland would put residents in coastal communities at grave risk even when the forecast of the path of the storm is accurate. Communities simply might not have enough time to prepare for a hit from a major hurricane, especially if the forecast had been for a much less intense storm.

A recent example of this dangerous scenario is one that occurred along the Texas coast in 2007. In just 24 hours, a tropical depression with a sustained wind of 29 mph blossomed into 92-mph Hurricane Humberto and moved inland just northeast of Galveston. Since Humberto moved inland as a Category 1 hurricane, the weakest category, wind damage was still fairly light, but the rapid intensification was an indication of the potential danger.

A more intense example of rapid intensification occurred in Central America in 2007, when a tropical depression (with winds of no more than 38 mph) rapidly intensified into the Category 5 Hurricane Felix with 175 mph winds within two days. The storm was over open water at the time of its initial intensification, but after weakening, it quickly re-intensified back into a Category 5 storm just before moving inland, killing dozens and causing severe damage in Honduras and Nicaragua.

During the rapid intensification phase of the storm, the National Hurricane Center's best computer model -- one of the tools that forecasters depend on for forecasting the intensity and track of a storm -- didn't even forecast that the depression would become a minor hurricane, let alone a major Category 5 storm. The model forecast wind speeds to increase to just 70 mph.

The National Hurricane Center, of course, understands the implications of an inaccurate intensity forecast, especially when it happens close to land, and that's a major reason for the goal of improving intensity forecasts.

But it's important to understand how much the improvement of hurricane forecast accuracy has already benefited society. A 2007 report from the National Hazards Review states that "forecasting in the late 20th century prevented 66 percent to 90 percent of the hurricane-related deaths in the United States that would have resulted from techniques used in the late 1950s."

Those impressive statistics are mainly the result of improved location forecasts, which are more accurate now for many reasons, including increased knowledge about tropical-type storms, improved data collection, the advent of the weather satellite and computer models to assist forecasters.

As intensity forecasts improve as well, the number of lives saved will increase.