Also, The Hurricane Center Doesn’t Overestimate…But It Does Over-warn

Today marks 4,001 days since the last major hurricane (Wilma in 2005) made landfall in the United States. A major hurricane (Category 3 to 5) has maximum sustained winds of at least 111 mph, and “landfall” means the center of the hurricane eye crosses the coastline.

This morning it looks like Matthew will probably not make landfall along the northeast coast of Florida. Even if it does, its intensity is forecast to fall below Cat 3 strength this evening. The National Hurricane Center reported at 7 a.m. EDT that Cape Canaveral in the western eyewall of Matthew experienced a wind gust of 107 mph.

(And pleeeze stop pestering me about The Storm Formerly Known as Hurricane Sandy, it was Category 1 at landfall. Ike was Cat 2.)

While coastal residents grow weary of “false alarms” when it comes to hurricane warnings, the National Weather Service has little choice when it comes to warning of severe weather events like tornadoes and hurricanes. Because of forecast uncertainty, the other option (under-warning) would inevitably lead to a catastrophic event that was not warned.

This would be unacceptable to the public. Most of us who live in “tornado alley” have experienced dozens if not hundreds of tornado warnings without ever seeing an actual tornado. I would wager that hurricane conditions are, on average, experienced a small fraction of the time that hurricane warnings are issued for any given location.

The “maximum sustained winds” problem

Another issue that is not new is the concern that the “maximum sustained winds” reported for hurricanes are overestimated. I doubt this is the case. But there is a very real problem that the area of maximum winds usually covers an extremely small portion of the hurricane. As a result, seldom does an actual anemometer (wind measuring device) on a tower measure anything close to what is reported as the maximum sustained winds. This is because there aren’t many anemometers with good exposure and the chances of the small patch of highest winds hitting an instrumented tower are pretty small.

It also raises the legitimate question of whether maximum sustained winds should be focused on so much when hurricane intensity is reported.

Media hype also exaggerates the problem. Even if the maximum sustained wind estimate was totally accurate, the area affected by it is typically quite small, yet most of the warned population is under the impression they, personally, are going to experience such extreme conditions.



How are maximum sustained winds estimated?

Research airplanes fly into western Atlantic hurricanes and measure winds at flight level in the regions most likely to have the highest winds, and then surface winds are estimated from average statistical relationships. Also, dropsonde probes are dropped into high wind regions and GPS tracking allows near-surface winds to be measured pretty accurately. Finally, a Stepped Frequency Microwave Radiometer (SFMR) on board the aircraft measures the roughness of the sea surface to estimate wind speed.

As the hurricane approaches the U.S. coastline, doppler radar also provides some ability to measure wind speeds from the speed of movement of precipitation blowing toward or away from the radar.

I don’t think we will solve the over-warning problem of severe weather events any time soon.

And it looks like the major hurricane drought for the U.S. is probably going to continue.