What You Need to Know About Hurricanes

Hurricane season started on June 1st in the North Atlantic, and by June 5th we had our first named storm, Tropical Storm Andrea. Many experts have predicted that this year’s season could be worse than average, so let’s take a look at what we need to know to prepare for the upcoming months.

Strong tropical storms go by many different names, though they all follow the same basic pattern. Hurricanes, typhoons, and cyclones generally form over warm “tropical” bodies of water due to the evaporation of water from the ocean surface, which then condenses into clouds and falls as rain. The storms rotate around an eye, that when well-defined can be calm and nearly cloud-free (which can trick people into thinking the danger is over when really they’re just in the eye of the storm). Rotation is caused by the Coriolis effect, which causes storms to rotate counter-clockwise to the north of the equator and clockwise to the south (and explains why cyclones rarely form within 2° the equator, since the effect isn’t strong enough there to cause storms to rotate). Winds are generally strongest close to the center of the storm.

Photo of a hurricane as seen from space.
Hurricane Isabel, as seen from the International Space Station on September 15, 2003. Note the well-defined eye of the storm. Photo by Ed Lu, via Wikipedia.

Tropical storm seasons fall at different times of the year around the world, usually from late spring through fall, though occasionally storms may form somewhat outside these dates. Outliers are a generally assigned to the season defined by the calendar year in the northern hemisphere or a cyclone season running from July 1 – June 30 in the southern hemisphere.

World map showing paths of cyclones, most of which were concentrated in the north Atlantic, north Pacific, south Pacific near Australia, and parts of the Indian Ocean.
Map of all tropical cyclones that formed from 1985 to 2005. Note the gap near the equator and the almost total absence of storms in the southeast Pacific and south Atlantic. Image via Wikipedia.

Hurricanes can cause damage in several different ways. High winds can damage buildings and snap trees and utility poles. Heavy rains can cause flooding, especially in low-lying areas and near lakes and rivers. High waves can destroy structures near the ocean, flip boats, and cause coastal erosion. On the side of the storm where winds are blowing onshore, a storm surge can cause additional flooding. Sometimes isolated tornadoes can even form during hurricanes.

Storm intensity is measured on several different scales depending on what region the storm is affecting. In the US, we mostly hear about the Saffir-Simpson hurricane wind scale (SSHWS), which classifies storms by their maximum sustained wind speeds.

  • Tropical depression: Sustained winds less than 38 mph
  • Tropical storm: Sustained winds 39-73 mph
  • Category one hurricane: Sustained winds 74-95 mph
  • Category two hurricane: Sustained winds 96-110 mph
  • Category three hurricane: Sustained winds 111-129 mph
  • Category four hurricane: Sustained winds 130-156 mph
  • Category five hurricane: Sustained winds above 157 mph

The SSHWS has been criticized for not taking into account other factors that can affect how much damage a storm causes, such as rainfall amounts, storm surge, and overall size. Unlike tornadoes, which are classified after the fact based on storm damage, hurricanes last much longer, are evaluated as they form, and we can take reasonably frequent wind measurements to see if the storms are weakening, gaining strength, or holding steady. Satellite imagery even enables us to categorize storms that never make landfall, and thus cause no little-to-no damage (though outer bands of rainfall may reach land even if the eye doesn’t, wave activity may increase on nearby coastlines, and ships may be rerouted to avoid the storms).

When systems reach tropical storm strength, they’re given names. There are six sets of names currently in rotation, though when a storm is particularly damaging its name may be retired and replaced with a different one. For example, three names in the queue for this year have never been used before; Dean, Felix, and Noel were retired after the 2007 hurricane season. The names are assigned alphabetically, with alternating (traditionally) male and female names, though the letters Q, U, X, Y, and Z are not used. On the rare occasions that there are more than 21 named storms, the following storms are named after the letters in the Greek alphabet.

What should you do if you’re in the path of a hurricane about to make landfall? The most important thing you can do is to obey evacuation orders if they’re in place. There’s always the possibility that a storm will weaken or turn at the last minute, but computer models have gotten pretty good at figuring out where storms will go, especially as they get closer to shore (though U.S. predictions could be better; the National Weather Service took a few days longer to figure out that Hurricane Sandy would turn inland than the European storm models, meaning there was less time for people to plan). Public officials don’t like to cause panic for no reason, especially since false alarms make people less likely to comply with future orders, so if they’re confident enough in the forecast to tell you to get out”¦ get out. Once the storm hits, it may be too dangerous for emergency services to rescue you from flooding or buildings damaged by wind or fire. If you do plan to ride out a storm, there are several steps you should take to prepare yourself and your home.

  • Gather up the supplies you’ll need if you lose power. You’ll need non-perishable, ready-to-eat food, plenty of water (one gallon/person/day, you can buy bottled water and/or fill up the bathtub), a weather radio, a first aid kit, medications, candles and matches or battery-operated lights, and more. has a comprehensive list of what you should keep in your disaster supply kit.
  • Find out ahead of time where local storm shelters are located and map out multiple routes to get to them. If you leave your house after the storm has started, do not drive on flooded roadways. Your car may stall or be washed off the road.
  • If you don’t have hurricane shutters, you may need to board up your doors and windows.
  • Secure or bring inside any objects in your yard that could be picked up by the wind, including patio furniture, grills, and bikes.
  • Trim back any dead tree branches that could break off in high winds and damage your house or property.
  • Clean out any storm drains you may have on or near your property so that they’re less likely to overflow.
  • Make sure you have a full tank of gas in your car.

Even if you don’t live on the coast, you may not be immune to hurricane damage. I’ve lived in upstate New York for two years and have been through three hurricanes or tropical storms, plus several other heavy rainstorms from systems that had lost intensity by the time they got to us. Irene, Lee, and Sandy all downed trees in my yard or neighborhood, caused flash flooding on local rivers, and flooded houses all around us. (Lee destroyed quite a bit of furniture and other items that had been temporarily stored in our garage since we had moved in not long before. Wiped out all the carpet downstairs too. And many people had it far, far worse.) If you’re not in the direct path or on the coastline you’re unlikely to be evacuated, but you should still pay attention to weather reports to see what precautions you need to take.

After the storm, it’s just as important to comply with orders from local officials. If you’ve evacuated, don’t try to return home until after your area has been declared to be safe. Flood waters may be polluted, so you should stay out of them if at all possible. Widespread power outages may take quite a while to repair. If your home was damaged by the storm, you may be able to get compensated by FEMA or your insurance company (though regular homeowners insurance does not cover flooding; you’ll need to buy additional insurance well in advance for that). If you are unaffected and want to help hurricane victims, it’s generally better to donate to long-established groups than small charities that pop up in the immediate aftermath, since it’s hard to know if they’ll actually distribute funds as promised (whether due to intentional fraud or simple ignorance of logistics and what’s really needed). Unless you’re in the area affected, it’s also usually better to donate money than goods, since the cost of transporting and sorting donations can be prohibitive.

By [E] Hillary

Hillary is a giant nerd and former Mathlete. She once read large swaths of "Why Evolution is True" and a geology book aloud to her infant daughter, in the hopes of a) instilling a love of science in her from a very young age and b) boring her to sleep. After escaping the wilds of Waco, Texas and spending the next decade in NYC, she currently lives in upstate New York, where she misses being able to get decent pizza and Chinese takeout delivered to her house. She lost on Jeopardy.

4 replies on “What You Need to Know About Hurricanes”

Apparently the vertical wind shear in those areas is pretty strong and while that can cause big thunderstorms, it doesn’t allow storms to rotate and form into cyclones very often. Not sure why those areas have so much wind shear, though. I’ll look into it more!

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