Posted: 8:20 am Friday, April 22nd, 2011
By Eliot Kleinberg
ATLANTA — Forecasts of a storm’s strength 12, 24 and 36 hours out — those periods when people already have raised up storm panels, laid in supplies, and in some cases headed out of town — actually were, on average, less accurate than they had been in the last five years, the National Hurricane Center said in a summary issued this month. (PDF)
The margin of error of about 8.7 mph at 12 hours out, and 16 mph at 36 hours out, is significant in that storm strength is exponential; a 20 mph jump from 75 mph to 95 mph can result in seven times the damage.
The hurricane center summary said errors were about average at two days out and above average at three, four and five days out.
Reporting from the National Hurricane Conference
Click here to see our stories from this week’s National Hurricane Conference in Atlanta:
The center, and other meteorologists, have said for years that, while they’d made great strides in forecasting storm paths, they’re still struggling with intensity forecast, and have devoted a lot of their research in that arena, as well as predicting when storms will form in the first place.
And, “We still get surprised when a storm falls apart,” hurricane center specialist Michael Brennan said in an interview at the conference. He cited Hurricane Tomas in 2010, which, as it approached the southern Bahamas, showed signs it would strengthen more, then dissipated.
|Last year, errors in predicting storms’ strength actually were larger on average than for the previous five years when it came to 12, 24, and 36 hours out and about even for 48 hours. They were better than average at 3, 4 and 5 days:|
Hours from landfall 12 hrs 1 day 36 hrs 2 days 3 days 4 days 5 days 2010 error (in mph) 8.7 13.8 16 17.8 19.2 21.2 21.4 2005-2009 error (in mph) 8.1 12.3 15.1 17.5 21.4 21.5 23.1
While doctors can learn a lot about what a person will become from watching how he or she develops as an infant and toddler, what storms do early often doesn’t give good clues about what it will do later, hurricane center director Bill Read said in an interview this week at the conference.
“Just look at Andrew,” he said.
The catastrophic hurricane came off the African coast 10 days before it struck on Monday, Aug. 24, 1992, and became a tropical storm seven days from landfall. But four days before it hit, it had degenerated to a “disorganized system” threatening to dissipate. Two days before it struck, forecasters were telling South Floridians to go about their business for the weekend.