Unless you’ve been living in a cave and isolated from all media you have heard of the devastation caused by Hurricane Michael beginning with it’s landfall at New Mexico Beach, Florida in the Panhandle of the state on October 10th. The forecasters at the National Hurricane Center in Miami, Florida did an excellent job of predicting the area of landfall and the strength of Michael’s winds. Michael was a category 4 hurricane with highest sustained winds of 155 miles per hour. That’s just 2 miles per hour shy of being a Category 5 storm with winds of 157 miles per hour or greater according to the Saffir-Simpson Wind Scale.
Herbert Saffir, a civil engineer, and Dr. Robert Simpson, then Director of the National Hurricane Center (NHC), devised the special wind scale in 1971 as a means to explain to the public the potential danger caused by tropical cyclones as the storm’s sustained winds increase.
The following is the detailed description of the scale from the National Oceanic and Atmospheric Administration (NOAA) NHC.
Category 1 – Sustained winds 74-95 mph (64-82 kt) (119-153 km/hr) – Very dangerous winds will produce some damage: Well-Constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap, and shallowy rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days.
Category 2 – Sustained winds 96-110 mph (83-95 kt) (154-177 km/hr) – Extremely dangerous winds will cause extensive damage: Well-Constructed frame homes could sustain major roof and siding damage, many trees will be snapped or uprooted, blocking many roads. Near-total power loss is expected with outages that could last from several days to weeks.
Category 3 (major) – Sustained winds 111-129 mph (96-112 kt) (178-208 km/hr) – Devastating damage will occur: Well-built framed homes may incur major damage or removal of roof decking and gable ends, Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes.
Category 4 (major) – Sustained winds 130-156 mph (113-136 kt) (209-251 km/hr) – Catastrophic damage will occur: Well-built frame homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.
Category 5 (major) – Sustained winds 157 mph or higher (137 kt or higher) (252 km/hr or higher) – Catastrophic damage will occur: A high percentage of framed homes will be destroyed,with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months.
When taken at face value these 5 categories seem to set up the criteria that give the public a pretty good idea what to expect from each category of storm and just how serious their local situation would be. I’m sorry, but that is not the case. As with the last few serious hurricanes to make landfall the wind predictions did not give an adequite estimation of the danger involved. The statistic that most people don’t know about is that the majority of deaths related to hurricanes result from water. The tremendous storm surge that runs over the shoreline and the exceedingly heavy rainfall amounts caused by the powerful and repetitive rain bands that are generated by the cyclonic spin of the air around the hurricane itself produce catastrophic flooding.
A recent article posted October 8, 2018 on Popular Science’s popsci.com site tackled this issue with the title “Hurricane categories consider wind speed but ignore one of the deadliest effects.” The article was written by Dennis Mersereau and here is his opinion on eliminating the use of the Saffir-Simpson Wind Scale. “As a weather reporter who’s spent years trying to talk about threatening hurricanes, I don’t think that’s entirely possible. The categories we use to describe wind strength in hurricanes is too deeply ingrained in the weather education of the United States to be able to completely remove it from the discussion. We have to work with the scale so that people in harm’s way pay proper attention to the winds, but also focus on the hazards posed by heavy rain and storm surge.”
As to whether a 6th category should be added to reflect the stronger hurricane wind we’ve been seeing I refer to a 1999 interview with Robert Simpson in Mariner’s Weather Log where he said ” when you get up into winds in excess of 155 miles per hour [note: the starting line for Category 5 at the time] you have enough damage if that extreme wind sustains itself for as much as six seconds on a building it’s going to cause rupturing damages that are serious no matter how well it’s engineered. It may only blow the windows out, but on the other hand, it can actually rupture the stairwells, the elevator wells and twist them, and it’s happened in many buildings so that you can’t even use the elevators after they’ve experienced this. So I think it’s immaterial what will happen with winds stronger than 156 miles per hour. That’s the reason why we didn’t try to go any higher than that anyway.”
It seems that if we’re going to help people better understand the dangers of specific tropical cyclones to their area that a combination of the wind scale and the expected effects of water (storm surge and rain) have to be added to the mix. It will be up to the public, as individuals, to heed the warnings or ignore them at their own risk.
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