FORT LAUDERDALE, Fla. — Imagine knowing six or seven days in advance where a tropical storm or hurricane might strike land. It would give residents, businesses and the military plenty of time to prepare.
The National Hurricane Center hopes to make that happen, but such long-range forecasts still are three to four years away because errors remain too large.
“We’ll likely need a few more seasons to verify the accuracy of these forecasts,” senior hurricane specialist Dan Brown said.
As of last season, the average six-day forecast track error was about 260 miles and the seven-day error about 315 miles. That’s about as good as four- and five-day track forecasts were a decade ago.
It’s also a marked improvement over two years ago, when the average seven-day error was about 400 miles. Yet even with the improved predictions, a storm projected to hit one city could actually slam into another..
Currently, the hurricane center tracks storms out to five days, with an average error of about 190 miles, about half of the average error in 1990, thanks to more sophisticated models and powerful supercomputers.
Forecast tracks can be found in the cone of uncertainty graphic on the hurricane center’s website, nhc.noaa.gov, when storm advisories are issued.
The hurricane center started experimenting with six- and seven-day forecasts in 2012 as part of an ambitious plan to sharply improve all storm predictions.
Hurricane Sandy, one of the test cases, showed the long-range projections need a lot of work. A week in advance, the system was predicted to aim out into the North Atlantic. Yet it slammed into the East Coast as a “post-tropical” system, causing almost $50 billion in damage and killing 72 people.
“Sandy was a case that didn’t work well,” Brown said of the seven-day forecast. “It wouldn’t have shown the threat to the United States that materialized.”
Under another in-house experiment, the hurricane center is trying to develop watches and warnings for disturbances before they become storms or hurricanes. The idea is to make sure coastal residents are alerted in time to make preparations in case a system develops close to the shoreline.
That happened with Gaston, which quickly grew into a hurricane before hitting South Carolina in August 2004, and with Humberto, which grew from a tropical depression into a hurricane in less than 24 hours before striking Texas in September 2007.
Such watches and warnings could be issued in the 2015 or 2016 storm seasons. “For now, we can only can issue a strongly worded tropical outlook,” Brown said.