How are hurricanes Measured? (Saffir Simpson Hurricane Scale)

Summary: What exactly is a hurricane and how are they measured? Are you brave enough to fly into a hurricane as the hurricane hunters do?

The past events surrounding the devastation of New Orleans, due to the impact of Hurricane Katrina have no doubt touched us all. How many of us could have imagined that the images that we have seen on the news could happen here: muddy, contaminated flood waters waist-high; people without adequate food, shelter, or bathroom facilities; families being split apart, not knowing if their loved ones are alive or dead; children taking care of children, people looting stores not for expensive electronics, but for milk and diapers for their infants who are crying from the heat; the dead being dragged off into corners because there’s nothing else to do. And there are those who just don’t know what else to do, so they leave the shelters and wander with no real idea of where they’re going or what’s going to happen. There’s a name for all of these folks: refugees. Right here in our own country.

So how does such devastation happen? We watched in horror the all but total destruction caused by the oceanic earthquake and subsequent Tsunami in Southeast Asia, and monsoons ravage Bangladesh almost yearly. Here on our own turf we understand the risk of living on the fault lines of California and Tornado Alley, but it’s accepted as fact that New Orleans has been living on borrowed time: sooner or later a major hurricane was going to hit, and since New Orleans is below sea level and water seeks it own level the destruction was bound to be total.

So exactly what is a hurricane anyway?

In order to be considered a hurricane a storm must have these characteristics:

· They occur during hurricane They must be tropical or generate near the equator
· They must be cyclonic – that is, they must revolve around a central “eye”
· They must be of low barometric pressure (the lowest pressures ever recorded were during hurricanes
· The cyclonic winds must sustain a speed of at least 74 miles per hour.

Unlike tornadoes, which form over land, hurricanes form over warm tropical waters of at least 80 degrees Fahrenheit (27 degrees Celsius) usually starting off as thunderstorms. Before a storm becomes a full-fledged hurricane though, it moves through two other stages. It is first classified as a Tropical Depression, which has the hurricane’s tell tale swirling rain and clouds yet lacks the power with winds reaching only 38 mph. Once wind speeds reach 39mph it is considered a Tropical Storm.

Like so many things in nature, science doesn’t understand exactly how hurricanes form. What science does know is that all hurricanes occur during “hurricane season,” (between June 1st and November 30th and must have three characteristics. First, it must have a continuing cycle of warm and humid oceanic air repeatedly condensing and evaporating. The clouds and rain created by this release heat (latent heat condensation) which warms the cooler air above which forces it to rise. This becomes a cycle, with more humid air rising which creates cyclonic winds. Next, hurricanes also must have “converging winds,” meaning that winds must literally collide and in doing so, push air upward, while winds at the higher altitudes remain strong and uniform. Lastly, a hurricane’s barometric pressure must be different at the surface than at higher altitudes.

How do scientists classify hurricanes?

Hurricanes are rated using the Saffir-Simpson Hurricane Scale that assigns a rating of 1-5 based on the hurricane’s present intensity. The primary factor taken into consideration in the Saffir-Simpson scale is wind speed over one minute and the scale is used to predict the amount of damage expected once the hurricane hits land.

Category one storms have a maximum wind speed of 95 mph with waters surging up to five feet above normal. Building damage is almost non-existent (with the exception of mobile homes). Some greenery damage and minimal coastal flooding can be assumed.

Category Two winds top out at 110 mph with storm surges up to 8 feet higher than average. Some damage to doors and windows, as well as roofs, can be expected. Some trees will be blown down, but not uprooted. Damage to mobile homes as well as piers can be expected. Coastal flooding up to 4 hours before the hurricane center hits.
Category Three winds move winds up to 130 mph with surges up to 12 feet above normal. Land lower than 5 feet below sea level can be flooded as far as 8 miles from the coast. Structural damage to small homes and out buildings can be expected as well as large trees down. Mobile homes can be assumed totaled. Escape routes that are considered low can be assumed cut off by rising water levels as early as 5 hours before the eye of the storm hits. Larger, well-constructed coastal structures will most likely sustain damage and smaller coastal structures destroyed due to violently floating debris.

Category Four winds can have winds up to 155 mph and with surges of up to 18 feet above mean. Land 10 feet below sea level may require major evacuation efforts up to six miles inland. Total roof structure failures of small homes and total destruction of all mobile homes.

Category Five storms are marked by winds in excess of 155 mph with surges of at least 18 feet above normal. Total evacuation of low land is necessary. Residences and industrial buildings will most likely sustain complete roof failure as well as total building failure in some cases. Buildings lower than 15 feet above sea level and within 5 miles of the coast will sustain floor damage. There have been only three Category Five storms in the recorded history of the United States. The latest being Hurricane Katrina.

How do scientists track hurricanes? It’s really not all that complicated even though all of the characteristics of the storm can change on a dime. Unfortunately, it’s for the exact same reasons that it can be incredibly difficult to predict the path a hurricane will take. By using satellite and infrared photography, visuals and Doppler, scientists are able to plot the longitude and latitude of a hurricane at regular intervals. Meteorologists can then make as educated a guess as possible as to the direction a storm might go. For instance, the chart below shows the path of a phantom hurricane:

hurricane tropical storm (from enchantedlearning.com)

The most dynamic way that storm information is gathered and hurricanes are tracked is by using information collected by the members of the 53rd Weather Reconnaissance Squadron/403rd Wing out of Keesler Air Force Base located in Biloxi, Mississippi. Known as the Hurricane Hunters, this very small and very special branch of the military was initiated by the Department of Defense in 1944 specifically to fly directly into tropical storms and hurricanes. Using a plane identical to the cargo craft WC-130, but loaded to the teeth with extremely specialized weather sensing computers and other equipment, the Hurricane Hunters can fly five missions a day in the hurricane region

3 thoughts

  1. The WC-130Js are not exactly “loaded to the teeth with extremely specialized weather sensing computers and other equipment”. They actually only have not much more than the basic equipment required to observe the tropical and also winter storms, which can be worse than a hurricane being much bigger in size.

    The WP-3Ds flown by NOAA’s Aircraft Operations Center at McDill AFB, FL, are the aircraft “loaded to the teeth with extremely specialized weather sensing computers and other equipment” mainly used for research as well as routine storm monitoring.

    In theory, if all 10 WC-130Js were mission ready, the 53WRS could fly more than 10 missions per day if they could crew all the missions, each an average of 14 hours to cover at least three 6-hourly fixes. Standard crews are limited to fly no more than 16 hrs/day.

    But each tropical storm only requires 2 to 3 missions per day to keep track of it, if so tasked by the NHC. Not every 3 to 6 hourly fix is tasked, mostly dependent on the proximity to land or other US interests. There are times when 3 or more tropical systems have been around on any one day. This is when NOAA helps out with their 2 aircraft and crews, or if a storm is unusual as to merit their attention for research purposes.

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