I heard on my car radio a news report interviewing hotel and resort property owners on the East Coast that lost virtually all their bookings this holiday weekend due to warnings for hurricane Earl. A direct quote from one of the people interviewed was:
It was the storm that wasn’t
The Shelter Island Reporter in the Long Island area seems to like that phrasing too for their story:
Rain, heavy at times, is all the Island got from Earl, which was downgraded to a tropical storm by 11 p.m. Strong winds did not reach Shelter Island. The rain total on Shelter Island for Friday was 1.71 inches
About the same time, an email from my friend Jan Null, former lead forecaster for the NWS in San Francisco showed up on my phone. He’s railing on about the bad reporting in the media, which I can understand, because TV networks have been chomping at tghe bit to get a new hurricane lead story, and with the holiday weekend mixed in, it was a perfect media storm. Though, with not much actually happening inland, some reporters were perhaps stretching a bit.
In watching and listening to coverage of Hurricane Earl, I have heard way too many “meteorologists” speak about “hurricane force gusts”! There’s no such thing! The amount of force of a gust is significantly less than the sustained winds that define a hurricane.
Here’s what I wrote for a piece in Examiner.com last year (http://www.examiner.com/sf-in-san-francisco/meteorological-pet-peeves-part-1-of-3 )
“Hurricane Force Winds” It seems that anytime there is a wind gust over about 60 mph the airwaves and other sources, including NWS statements, are rife with the expression “hurricane force” winds. While this might be good for conveying that it’s windy and might be dangerous, it’s both bad meteorology and bad physics! (And calling it a hurricane force gust doesn’t make it right either) Let’s start with some basics. The threshold for hurricane winds is when the 1-minute sustained winds equal or exceed 74 miles per hour.
Please note the word “sustained”! According to the NOAA Hurricane Research Division, peak 3 to 5-second gusts are approximately 30% higher than their associated sustained winds. This means that a 74 mph sustained wind of a minimal hurricane has gusts in the range of 96 mph. Quite a difference. But that’s just the wind speed.
What about the amount of force from the wind onto a surface that is perpendicular to the wind? From high school physics we remember that the force associated with a given speed is proportional to the square of the wind speed. (For the overachievers out there, the formula to calculate this force is: F = .00256 x V^2, where F is the force in pounds per square foot (psf), and V is the wind velocity in mph)
Consequently, the amount of force with a 74 mph gust is 14.0 psf, while the force from a 96 mph gust is 23.6 psf; or 69% higher. The bottom line is that a gust to 74 mph is NOT even close to hurricane force!
Certified Consulting Meteorologist
Golden Gate Weather Services