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June 30, 2010 / Dave Gorham

All Eyes on Alex

If you’ve been around the computer or watched any television this week, you know the main story has been Hurricane Alex. For the past several months here at ImpactWeather, we’ve been calling for an above average hurricane season. Here it is the end of June and we have our first named storm of the Atlantic Hurricane Season. The big question on everyone’s mind has been where it will make landfall and what type of effect could a hurricane have on the oil spill? To answer the first question, Hurricane Alex looks to make landfall tonight into early Thursday in northeast Mexico. As far as what type of effects a hurricane in general could have on the spill zone, you can check out the five-minute video we produced that addresses the issue.

Hurricane Alex is currently located near 23.3N/95.1W or 235 miles southeast of Brownsville moving west-northwest at 7 mph. It’s a Category 1 hurricane with maximum sustained winds near 80 mph. Some strengthening will be possible and it could become a Category 2 hurricane with maximum sustained winds near 100 mph prior to landfall about 120 miles south of the Texas border.


Forecast track of Hurricane Alex.. Image: ImpactWeather

In 2006, ImpactWeather introduced the Hurricane Severity Index (HSI) which is an enhanced hurricane rating system that more accurately defines the strength and destructive capability of a given storm than other scales. The HSI uses comprehensive equations which incorporate not only the intensity of the winds but the size of the area the winds cover.

Saffir-Simpson Hurricane Scale vs HSI. Image: ImpactWeather

To put this into perspective, the current HSI for Hurricane Alex is a 10 on our 50-point scale, with 5 points attributed to its size and 5 for its intensity. The HSI is based on both intensity and size, whereas the Saffir-Simpson is solely based on the hurricane’s maximum sustained wind speed in any single area, regardless of how large or small the area is. Why is there a need for a new hurricane scale? The Saffir-Simpson scale is only based on max winds and these winds may be isolated. Storm surge is more related to a hurricane’s size and the HSI takes size into account, whereas the Saffir-Simpson doesn’t. It also doesn’t provide a good estimate of potential damage nor does it encompass tropical storms. For instance, Tropical Storm Allison was the first named storm of the 2001 season and it hit Southeast Texas with torrential rains. The worst flooding was in the Houston area. Maximum sustained winds reached 60mph but when you look at the size of this storm, there were tropical storm force winds extending 230 miles to the east of the center. The Saffir-Simpson scale wouldn’t have even been applied to Tropical Storm Allison.

How valuable is the HSI?  Take a look at the comparison of Ivan ‘04 and Dennis ‘05 below. Same location in the Gulf, same “category 3” rating on the Saffir-Simpson scale . . . but take a guess which one was considerably more destructive and caused a considerably larger amount of damage.   Here’s a hint:  Dennis caused $2.23 billion in damage.  Ivan?  $13 billion.

Image: ImpactWeather

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