Hurricane Knowledge - Alabamas13.com WVTM-TV Birmingham, AL

Hurricane Knowledge

MOBILE, Ala. -

Hurricane Season in the Atlantic Ocean runs from June 1st through November 30th. It is the time of year when a mass of clouds near the equator can spin into a tropical storm or hurricane. These huge storms can be devastating to lives and property but they are just a part of natural cycles of moving heat and moisture from one place to another.

NOAA issues seasonal hurricane outlooks that you will find on the National Hurricane Center Website and so do private forecasters like Dr. Bill Gray at Colorado State University, WSI, AccuWeather, Earth Networks, Coastal Carolina University, and the NCSU Tropical Cyclone Prediction Team. All of these forecasts are for the entire Atlantic basin which includes the Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico so they don't tell you anything about any one city or county. Even in the quietest hurricane season one major hurricane where you live is all it takes to be a problem. Check the long term statistical probability of a hurricane landfall.

A Tropical Wave is a region of low pressure and cloudiness that moves from east to west in the tropics. These are a usual part of tropical weather just as we talk about highs and lows moving across the US.

A Tropical Disturbance is when thunderstorms develop and last for more than a day within a tropical wave. These are common.

An Invest is a disturbance that is being investigated by the National Hurricane Center. Invests have a number for computer tracking purposes but they should not be confused with a tropical depression that has a different number. Here's an in-depth description of what an invest is and isn't. If the tropical disturbance shows a circulation with the thunderstorms becoming organized it is called a Tropical Depression and given a number for tracking purposes. We show it as an "L" on our weather maps. At this point more attention is given to it as something that may develop further.

If the winds in a tropical disturbance exceed 38mph it becomes a Tropical Storm and it is then given a name from a pre-selected list. The winds in a tropical storm may range from 38mph to 73mph.

Subtropical is used to describe tropical depressions or tropical storms that are a hybrid between tropical and non-tropical. It's a technical distinction that doesn't change much about the impact at landfall.

If the tropical storm increases wind speed to 74mph or greater it is then called a Hurricane. A Major Hurricane is one that is a category 3 or higher.

Extratropical describes a system that was a tropical storm or hurricane but either merged with a front or regular region of low pressure. These can maintain strength for a while before fully weakening.

Tropical systems can form in several days or just one day. The water temperature needs to be at least 80 degrees in the top 150 feet of the ocean. The water temperature at the beach is not enough to influence a hurricane since the water is so shallow. Winds in the atmosphere must not change too much in direction and speed otherwise a storm would be shredded apart. As warm ocean water evaporates and condenses to form clouds, heat feeds the developing thunderstorms. The thunderstorms act together as they circulate to form a tropical storm.

Typical hurricanes are about 300 miles wide but they vary in size. The eye of the storm is relatively calm and between 20 to 40 miles across. The eyewall surrounding the eye has the highest winds. Hurricane force winds can extend outward 25 to 150 miles, while tropical storm force wind can stretch out as far as 300 miles. Outer rainbands that feed the storm can be 50 to 300 miles long. The right side of a hurricane path is the most dangerous when it comes to wind, flooding, and tornadoes. Do not focus on the eye or exact forecast track- Danger exists in a large area based on the storm size and based on the uncertainty in forecasting. Every storm is different based on the wind speed, the motion, the track the eye size, the hurricane wind radius, and the amount of rainfall. You can not just compare two hurricanes on any one of the above.

As Hurricanes or Tropical Storms approach land, first Watches are issued, then Warnings. The Watches tell you that the effects of either the Tropical Storm or Hurricane are possible within 48 hours while the Warnings tell you that the storm is likely to affect your area within 36 hours. During the Watch is when you make advance plans for safety and shelter. When the Warning is issued you must take immediate action for personal safety.

Technology and communication have helped to dramatically reduce hurricanes deaths in the last half century but as population and housing grow along the coastal areas we see a major increase in the dollar amount of damage. With higher population density the potential for major loss of life increases because not everyone may be able to escape harm in short notice. It is important to know that the 1960s through the 1990s were fairly quiet hurricane seasons compared to the 1930s and 1940s. It looks like we are returning to more active seasons.


Saffir-Simpson Hurricane Wind Scale

You know this scale as the category of a hurricane. The higher the hurricane-force wind, the higher the category. Damage produced by hurricanes in higher categories grows exponentially with the wind. While we tend to focus on a storm strengthening to the next category there is much more destructive difference between storms going from the lower end to the higher end of a single category.

Notice there is no longer a mention of storm surge in the scale. That's for two reasons- one is that storm surge is not an issue away from the coast but the second reason is more important and that is the wind speed at landfall and storm surge are not always related. Under the old Saffir Simpson scale Katrina's storm surge was two categories higher than the wind. A hurricane with weakening wind at landfall may still have a very high surge while a hurricane with increasing wind at landfall may have a small storm surge. Listen carefully as storms approach for both parts of the story. Needless to say we've seen storm surge from the most powerful storms at over 30 feet along the central Gulf Coast so the numbers can be large.

NOAA has a webpage dedicated to storm surge and coastal flooding.

A Category 1 hurricane has winds between 74 and 95 mph. Damage is minimal but winds are still dangerous.
People, livestock, and pets struck by flying or falling debris could be injured or killed. Older (mainly pre-1994 construction) mobile homes could be destroyed, especially if they are not anchored properly as they tend to shift or roll off their foundations. Newer mobile homes that are anchored properly can sustain damage involving the removal of shingle or metal roof coverings, and loss of vinyl siding, as well as damage to carports, sunrooms, or lanais. Large branches of trees will snap and shallow rooted trees can be toppled. Extensive damage to power lines and poles will likely result in power outages that could last a few to several days. Danny in July of 1997 was a category one but its biggest problem was from the more than 2 feet of rain that fell.

A Category 2 hurricane creates moderate damage with winds of 96-110mph.
There is a substantial risk of injury or death to people, livestock, and pets due to flying and falling debris. Older mobile homes have a very high chance of being destroyed and the flying debris generated can shred nearby mobile homes. Newer mobile homes can also be destroyed. Poorly constructed frame homes have a high chance of having their roof structures removed especially if they are not anchored properly. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks. Potable water could become scarce as filtration systems begin to fail. In August of 1995 Erin made landfall as a category 2.

A Category 3 hurricane produces widespread damage with winds of 111-129 mph.
There is a high risk of injury or death to people, livestock, and pets due to flying and falling debris. Nearly all older mobile homes will be destroyed. Most newer mobile homes will sustain severe damage with potential for complete roof failure and wall collapse. Poorly constructed frame homes can be destroyed by the removal of the roof and exterior walls. Unprotected windows will be broken by flying debris. Well-built frame homes can experience major damage involving the removal of roof decking and gable ends. There will be a high percentage of roof covering and siding damage to apartment buildings and industrial buildings. Complete failure of older metal buildings is possible, and older unreinforced masonry buildings can collapse. Numerous windows will be blown out of high-rise buildings resulting in falling glass, which will pose a threat for days to weeks after the storm. Most commercial signage, fences, and canopies will be destroyed. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to a few weeks after the storm passes. Opal in 1995, Ivan in 2004 and Dennis in 2005 were marginal category 3 at landfall while Frederic in 1979 was a high category 3 storm. Katrina in 2005 was also a high category 3 at landfall based on the wind even though storm surge along the Mississippi coast was more like that from a much stronger storm.

A Category 4 hurricane produces extreme damage with winds of 130-156mph.
There is a very high risk of injury or death to people, livestock, and pets due to flying and falling debris. Nearly all older (pre-1994) mobile homes will be destroyed. A high percentage of newer mobile homes also will be destroyed. Poorly constructed homes can sustain complete collapse of all walls as well as the loss of the roof structure. Well-built homes also can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Extensive damage to roof coverings, windows, and doors will occur. Large amounts of windborne debris will be lofted into the air. Windborne debris damage will break most unprotected windows and penetrate some protected windows. There will be a high percentage of structural damage to the top floors of apartment buildings. Steel frames in older industrial buildings can collapse. There will be a high percentage of collapse to older unreinforced masonry buildings. Most windows will be blown out of high-rise buildings resulting in falling glass, which will pose a threat for days to weeks after the storm. Nearly all commercial signage, fences, and canopies will be destroyed. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Long-term water shortages will increase human suffering. Most of the area will be uninhabitable for weeks or months.

A Category 5 hurricane is catastrophic. The winds exceed 156mph.
People, livestock, and pets are at very high risk of injury or death from flying or falling debris, even if indoors in mobile homes or framed homes. Almost complete destruction of all mobile homes will occur, regardless of age or construction. A high percentage of frame homes will be destroyed, with total roof failure and wall collapse. Extensive damage to roof covers, windows, and doors will occur. Large amounts of windborne debris will be lofted into the air. Windborne debris damage will occur to nearly all unprotected windows and many protected windows. Significant damage to wood roof commercial buildings will occur due to loss of roof sheathing. Complete collapse of many older metal buildings can occur. Most unreinforced masonry walls will fail which can lead to the collapse of the buildings. A high percentage of industrial buildings and low-rise apartment buildings will be destroyed. Nearly all windows will be blown out of high-rise buildings resulting in falling glass, which will pose a threat for days to weeks after the storm. Nearly all commercial signage, fences, and canopies will be destroyed. Nearly all trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Long-term water shortages will increase human suffering. Most of the area will be uninhabitable for weeks or months. Camille in 1969 was a category 5 in southern Mississippi and so was Andrew in south Florida in 1992.


Some people wonder why not just drop a bomb on a hurricane to weaken it. Part of the answer is that an average hurricane has the equivalent power each day of hundreds and hundreds of atomic bombs. If you release that much radiation in the atmosphere we are all in trouble. The other reason hurricane modification is tricky is because hurricanes happen in international waters and if a storm grows worse to strike another country there would be political problems. One final reason modifying hurricanes is not a good idea is because they are a vital part of the atmospheric processes to keep the Earth in balance. If you remove a part of the chain something worse could happen.

Some people wonder if increased hurricane activity is due to global warming. Global warming or climate change is a very slow process. The main cause of more hurricanes seems to be 20-30 year cycles in overall hurricane activity. The 1950s through the 1990s were much quieter than the 1930s and 1940s but many people have forgotten that. According to NOAA we are entering the increased activity portion of the cycle. Katrina occurred in this cycle as a rare exception where hundreds of people died. Realize that most Katrina deaths occurred after the storm passed when levees failed. After the active recent hurricane seasons we find the central Gulf Coast with a lot of lingering storm debris in our waterways and along the coastline. NOAA tries to keep track of the marine debris cleanup.

Tropical Storm names are alphabetical and agreed upon by an international organization of meteorologists in the World Meteorological Organization. Names alternate male and female, and represent names common in the countries where tropical storms may strike. There are no names used starting with Q, U, X, Y, Z because there are fewer common names starting with these letters. There are 6 years worth of names and the lists are recycled every 6 years. Only when a storm is very destructive is the name retired. In 2005 when we ran through all the names we used the Greek alphabet starting with Alpha, Beta, Gamma....


Most of Earth's surface is water and prior to satellites the formation of many tropical systems went undetected. In the 1960s satellites first gave us a view of developing tropical storms. In the 1970s radars presented a different perspective of tropical storms along the coastlines. We were clearly able to see rainbands and better understand what happens beneath the cloud canopy of a hurricane. Since then, meteorologists have developed sophisticated computer models to aid in projecting hurricane and tropical storm paths. These models are not perfect. They are only as good as our understanding of the atmosphere and the information that goes into them.

A big problem in hurricane forecasting is that there are very few data sensors over the oceans. We do not get hourly reports of temperature, wind, pressure and humidity as we do at hundreds of locations across the US. Satellites show the big picture but it is the details under the clouds that elude forecasters. As tropical storms grow and pose any threat to land, the US sends Hurricane Hunter aircraft into them to take readings. Even with the Hurricane Hunters we still don't get a frequent, detailed measurement of approaching hurricanes. In more powerful or threatening storms NOAA sends other research aircraft into storms as well in attempts to learn more about them.

Official hurricane forecasts for the US come from the National Hurricane Center, north of Miami. Meteorologists there focus their attention on the tropics. Using computer models, aircraft reports, data from buoys, satellite and radar, these experts have in recent years been able to project hurricane eye landfall to within 220 miles 3 days in advance. At 24 hours the accuracy is within 70 miles. This might not sound like accuracy to the average person but when you consider the size of the oceans and the complexity of the atmosphere, it is remarkable that forecasts can be this accurate. You can never expect the eye location to be so precise that you can disregard the hazards of an approaching tropical storm. Even when a prediction is right on target it is not just the eye of a storm where the weather can be deadly. Forecasting will never be 100% accurate so always be ready for change and updates. Along the central gulf coast we rely on the National Weather Service Office located at the Mobile Regional airport to issue local tropical storm advisories and bulletins.

Keep up with forecasts on TV, Internet and radio, as well as on your NOAA Weather Radio. At WKRG News5 we will give you frequent updates, and you can see our radar along with satellite loops on wkrg.com. You can follow current storms or view historic storms in our Hurricane Center. When tropical systems approach we do our best to give you the clearest picture of what might happen. However, no computer or person can guarantee tomorrow's weather. It is up to you to not put yourself in a position where you have no choices for safety when bad weather nears. If you wait until the last minute to take action, you increase risk. Stay safe!

Consider strengthening the building you live or work in. Find excellent tips and instructions from FLASH, the Federal Alliance for Safe Homes. Another organization with great information on safeguarding buildings and homes is the Institute for Business and Home Safety. Don't forget to have a safety plan for your pets.

There is a whole lot more to learn from National Hurricane Center Hurricane Awareness Website or NASA website for kids. Kids and grownups can learn more about hurricanes at FEMA's website for kids FEMA hurricanes and at the NASA Hurricane Website.

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