On June 1, the 2011 Atlantic hurricane season officially opens for business. If it is anything like 2010, business will be good. But, before we get into all that, we thought it might be helpful to answer a few questions for all of you who either don't know much about tropical weather or just moved here from, let's say, Michigan.
As we all listen to the nearly ceaseless discussion of forecast models, storm tracking and doomsday scenarios painted by local and national meteorologists, it's a good idea to understand at least a bit of what they are talking about. It's like when you visit a mechanic, it wouldn't hurt to have some inkling that the transmission is not the same thing as the engine.
So, to get you ready for the 2011 hurricane season -- along with batteries, bottled water, plywood and beer -- here are ten questions answered about tropical weather.
10. What is the history of hurricanes in Houston? When your city sits along the Gulf Coast, it is likely that it has weathered its share of hurricanes and the Houston-Galveston area is no different. Since they began tracking storms in the mid-1800s, the Galveston area has been struck by 18 hurricanes, including a number of major storms the worst of which was the 1900 hurricane. That storm killed more than 8,000 people and led to the development of the seawall. The area has gone as long as 18 years without a hurricane, but averages at least a nearby landfall every two years.
9. What are these category rankings we hear about all the time? Hurricanes are ranked on the Saffir-Simpson scale, which measures hurricanes based on sustained winds and the storm's central pressure. Like the Fujita scale for tornadoes, the Saffir-Simpson scale divides storms into categories. Category one is the lowest and category five the highest. The rankings have come under criticism for their lack of accuracy and their rigidity. Hurricane Ike, for example, was a category two based on wind speed and pressure, but had a storm surge more indicative of a category four storm.
8. High winds have to be the most dangerous part of hurricanes, right? High winds are scary, no doubt, but they do not account for most of the deaths or even damage during a hurricane. There is an old adage that goes, "Hide from wind, run from water." Hurricane winds, while dangerous, are not a significant threat to most modern homes. They, along with the tornadoes hurricanes spawn, can certainly damage homes and knock over trees, but the greater risk in a hurricane is from the storm surge -- the wall of water hurricanes push onshore. The storm surge during Ike destroyed entire communities along Bolivar Peninsula and wiped out virtually every pier and store on the Gulf side of the seawall.
7. What are sea surface temperatures and why do weather people talk about them?
One of the key factors to the development of hurricanes is the temperature of the ocean beneath them. The warmer the ocean, the greater the potential for hurricanes because they utilize this warm water to expand.
Sea Surface Temperatures (SSTs) include both the temperature at the surface and the depth of that "heat potential." Each year, a small area or eddy of warm water is spun off from the Gulf of Mexico's "loop current." To simplify, that super-heated warm water is like a superconductor for hurricanes. Both Rita and Katrina traversed that warm water eddy and blew up into massive hurricanes.
6. What other factors influence hurricane development? A wide range of upper-level atmospheric conditions, wind shear and even dust from the Sahara Desert blowing off the continent of Africa can affect storm formation in the Atlantic. Two key ingredients to storm formation are light upper-level winds and warm ocean temperatures. 5. Why does everyone talk about El Niño and La Niña when it comes to hurricanes?
El Niño and La Niña are atmospheric conditions affecting the Pacific Ocean. During El Niño years, super heating of the Pacific basin forces strong upper-level winds across the Atlantic, inhibiting the development of tropical storms. The exact opposite is true of La Niña years, which reduce winds across the Atlantic basin and result in much cooler Pacific temperatures. In 2010, there was a strong La Niña event in the Pacific and the Atlantic Ocean had one of its busiest hurricane seasons in years.
4. Why are some years much busier than others? Things like El Niño and La Niña are certainly contributing factors as are high SSTs, light winds and moderate African dust. The Atlantic basin also goes through 20- to 30-year periods of high activity followed by a similar amount of moderate to low activity. We are currently in the high activity period for storms and that is expected to continue for another ten to 15 years. It is also important to note that busy years do not necessarily mean lots of landfalls. In 2010, the U.S. had no significant landfall impacts from hurricanes, yet it had 19 named storms, 12 of which were hurricanes. Those same upper-level conditions that can spawn hurricanes affect their path.
3. Why aren't forecasts more accurate? If you watch the weather with any regularity, you know it is as likely that a 20 percent chance of rain means sunshine or downpours. The conditions in the upper atmosphere that affect weather are simply difficult to predict. When it comes to hurricanes, however, predicting the track of a storm is significantly better than forecasting intensity. When you consider the massive amount of space in the Atlantic basin, to predict the path of a storm to within 500 miles five days out is pretty incredible. Unfortunately, forecast computer models have a much tougher time predicting how big a storm will be than where it will go.
2. Why is the exact spot a hurricane hits so important? Hurricanes are, for the most part, fairly small. The most intense rain and winds are located around the center or "eye" of the storm. Most eyes range from 20 to 40 miles in diameter. Hurricane force winds (over 65 mph) don't often extend much beyond 100 miles out from the center of the storm. In addition, because of the counterclockwise rotation of storms, the worst winds and heaviest rainfall totals are on the north and east sides of the storm. As a result, someone 100 miles west of the center of the storm might only experience rain and some tropical storm force winds, while a person within 50 miles of the center to the east could get the worst the storm has to offer. By example, a storm making landfall on Galveston Island moving northeast would devastate Baytown but leave Katy with much more moderate conditions.
1. When should we evacuate? The obvious response here is if you are in an evacuation zone or in an area subject to storm surge, you need to go well in advance of any storm, preferably four to five days. The clusterfuck that was the Hurricane Rita evacuation in 2005 happened because a massive, scary hurricane was bearing down on us and people WAY out of the danger zones were running for their lives.
It's a very good idea to be prepared when the season starts. Have everything you need to take care of your yourself, your family, your pets and your home. If there is a huge storm headed our way and you truly feel unsafe, leave sooner rather than later. If you live 100 miles inland, you really should stay put unless your neighborhood floods easily or you have people with serious health concerns in your home so people who are in real, imminent danger can get to safety.
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