Hurricanes METEOROLOGY Lightning


The Wind


Tornadoes are extremely severe storms that are highly destructive. They appear as a dark, funnel-shaped cloud of violently rotating air that extends down to earth. The funnel appears dark as a result of sucking up debris.

The power and destruction of tornadoes is mind boggling! Tornadoes pick up debris that includes rocks, tree limbs, parts of buildings, etc. When the edge of the tornado funnel slams into a building, the debris acts like a circular saw ripping through everything it impacts.

Tornadoes have been known to pick up automobiles, horses, and whole trees. In one very strange incident, a tornado in Minnesota (year 1931) lifted an 83-ton railroad car containing 117 passengers and moved it 80 feet. The car was dropped into a ditch and all the passengers survived.

The following table shows the some of the most damaging tornadoes that have occurred in the United States:

Killer Tornadoes of the USA
Date Location Comments
May 27, 1896 St. Louis, Mo. 400 dead, 2500 injured
$12 million in damage
March 21, 1932 Alabama 268 dead, 1000 injured
March 21-22,1952 Arkansas, Missouri,
Tennessee, Alabama
343 dead, 1400 injured
February 21, 1971 Mississippi Delta 110 dead
August 28, 1990 Illinois 28 dead, 300 injured

Tornadoes result from the interaction of contrasting layers of air within a heavy cumulonimbus cloud mass. Atmospheric conditions required for the formation of a tornado include great thermal instability, high humidity, and the mixing of warm, moist air at low levels with cooler, drier air above.

The diameter of tornadoes can range from a few feet to a mile; most however are less than a quarter mile wide. Winds within a tornado can reach 200 to 300 mph (320 to 480 km/hr). The updraft at the center may reach 200 mph (320 km/hr). Updraft is caused by centrifugal (i.e. spinning) force that throws the air away from the center and causes a very low pressure area in the center.

The paths taken by tornadoes average about 16 miles (25km). Some tornadoes, however, greatly exceed that. In May of 1917, a tornado traveled across Illinois and Indiana leaving a path of destruction 293 miles (469 km) long! This tornado lasted 7 hours and 20 minutes.

A tornado that passes over water is called a waterspout. Several years ago, I saw a waterspout off the beach on Long Beach Island, New Jersey (USA). There were many thunderstorms in the area that day, and the seas were rough. I estimate that the waterspout was about five miles off shore.

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Precipitation is any form of water that falls to the earth's surface (and messes up the plans for your day off). Following is some interesting information on the various forms of precipitation:

Hailstones are balls of ice that range in size from raindrop size up to 2 or more inches (5 cm) in diameter. Hailstones as large as baseballs have been reported. Scientists believe that they form by repeated up and down trips, caused by violent updrafts in a thunderstorm. Hailstones become larger and larger with each up and down trip, until they become so heavy that they drop to the surface.

Rain is liquid water that reaches the earth's surface. Raindrops can range from small size (.02 inch or .05 cm) to large size (.25 inch or .6 cm). It is generally believed that rain drops initially form with the help of a condensation nuclei (e.g. a particle of dust, smoke, or salt). Once a small drop forms, it grows into a bigger drop by collision with other small drops. When the drop becomes large enough, it falls from the sky as rain.

Sleet is formed when rain passes through a layer of freezing air. The droplets freeze before they reach the earth's surface. This occurs when a warm air mass is above a cold air mass.

Drizzle is a very slow fall of small water droplets (less than .05 cm diameter). Drizzle is formed in low-lying stratus clouds.

Snow is formed when water vapor turns directly into ice crystals. Snowflakes are hexagonal in shape (six sided) and are quite beautiful.

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The year is 1622. As Captain of the treasure galleon, Nuestra Senora de Atocha , you are tense at the site of a dull red sunset caused by a thin haze of clouds. The air is hot and sticky. The ship's barometer is high, and the wind is dead.

The next morning a tight knot forms in your stomach as the swells begin to grow. You desperately try to sail the ship north along the Florida coast and away from the edge of the approaching storm. It is a desperate race. As the storm draws nearer, the ship's barometer suddenly drops. The wind steadily builds, to the point that the sails start to tear and shred. A huge rain cloud rushes forward from the horizon and the sky opens up into a torrential downpour. You desperately help the crew in reducing the sail size, and in doing everything you can to prevent the ship from capsizing in the 30 foot seas. You can barely keep your footing on the rocking deck as 100 mile per hour winds buffet the sea.

The last memory of your life is the screams of cracking timbers as a 40 foot monster wave brakes over the bow and drives the Atocha to its final watery grave.

The story above attempts to provide an accurate description of an approaching hurricane and how it would have been perceived in the 1600s. The story of the Atocha is true. The ship, which was discovered in 1985 by Mel Fisher, contained a treasure valued at more that $400,000,000. Today we are fortunate because we have advance warning of these terrible storms.

Very powerful cyclonic storms that form over warm tropical waters are called hurricanes, cyclones, or typhoons. These storms are called hurricanes in the West Indies, cyclones in the region of the Indian Ocean, and typhoons in the Pacific Ocean. Typhoons are usually much stronger and deadlier than the Atlantic hurricanes. This is because the Pacific Ocean is much larger than the Atlantic, and the typhoons have more time to "power-up" before striking land. In the rest of this article I will focus on hurricanes, but the information also pertains to cyclones and typhoons.

Hurricanes are the result of violent winds moving around a calm center, called the "eye" of the storm. They develop tremendous strength and are the most destructive of all storms. Hurricanes can be from 60 to more than 1,200 miles (100 to 2,000 kilometers) in diameter. The eye is usually 12 to 62 miles (20 to 100 kilometers) across. Hurricanes have a combination of severe weather events including very strong winds, torrential rains, severe thunderstorms, and sometimes waterspouts (tornadoes over water). An especially damaging feature of hurricanes is storm surge. This wall of water, created by high winds and variations in air pressure, causes severe damage when it slams into a coastline. Following is some information on a few killer hurricanes:

Killer Hurricanes
Date Location Comments
August, 1969 US Gulf Coast Hurricane Camille slammed Louisiana, Mississippi, and Alabama with winds up to 200 mi. (320 km) per hour.
August, 1979 Caribbean Hurricane David demolished the Dominican Republic
August, 1992 Bahamas, Florida, Louisiana Hurricane Andrew decimated Homestead, FL, Florida City, FL Morgan City, LA, and Lafayette, LA
September, 1992 Hawaiian Islands Hurricane Iniki was the most destructive storm to hit the Hawaiian Islands. Winds of up to 225 mi. (360 km) per hour were recorded

When a hurricane passes, it often looks as though the storm has ended when the eye passes overhead. In a short time, however, the eye moves on and the opposite side of the storm hits, once again bringing heavy winds and severe rains.

Hurricanes cause massive damage as they sweep over islands and peninsulas. When they strike a large land area, such as a continent, they slowly die because they are cut off from their source of energy (the warm tropical waters) and they encounter a lot of friction from the land.

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The background for this web page shows what an unusually bad discharge of lightning would look like. Most of us (desert dwellers excluded) have experienced the unbelievable power and awesome visual experience of a lightning strike. Some of us have experienced it too closely (later, I will fill you in on my terrible lightning strike experience).

The formation and discharge of lightning is a very interesting topic. I will discuss what happens, step-by-step, since it is a complicated process.

  1. Inside of a thundercloud there is a variety of severe conditions including rain fall, air currents rising and falling, and water droplets freezing. As a result of this activity, some drops of water in the cloud become positively charged.
  2. Ice crystals that form in the cloud obtain a negative charge.
  3. The positively charged particles group together in the upper part of the cloud to form a positive- charge center, and a negative-charge center forms at the lower part of the cloud due to the heavier weight of the ice crystals.
  4. A positive charge builds up on the ground just beneath the cloud to counteract the negative charge that formed on the lower part of the cloud.
  5. The positive charge on the ground and the negative charge on the lower part of the cloud continue to build up until there is sufficient energy to jump the gap between the cloud and the ground.
  6. A small electrical discharge, called a pilot streamer moves from the negative part of the cloud to the positive earth.
  7. A stronger discharge, called a stepped leader immediately follows and ionizes the air in its path.
  8. When the pilot streamer touches the earth, a high powered return streamer jumps from the ground and travels toward the cloud by the ionized air path caused by the stepped leader. This is the bright flash that we see during a lightning storm.
  9. Since there are usually multiple negatively charged areas within a thundercloud, these negative charges quickly move to the area that just discharged.
  10. A dart leader from the newly formed negative-charge center will discharge down the same path as the first discharge.
  11. A second return streamer travels up to the cloud. This process continues until all the charges in a cloud have been discharged.

As you can see, there is a lot more to a lightning strike than meets the eye!

How about some more interesting tidbits about lightning.......

  • The thunder that follows a lightning strike is caused by the super heating of air. As the air is heated, the gases expand rapidly which causes compression waves (sound).
  • Sheet lightning is caused when lightning jumps from cloud to cloud.
  • Ball lightning is a ball shaped electrical discharge. Ball lightning often produces whistling sounds as it moves through the air.
  • Heat lightning is the reflection of distant lightning on clouds.
  • Lightning has been observed on other planets including Jupiter, Venus, Saturn, Uranus, and Neptune.
  • About 3,500 thunderstorms occur at any one time on the earth.
  • About 100 lightning strikes hit the earth every second.
  • Lightning produces chemical compounds (nitrates) that eventually fall to earth and supply nutrients to the soil.

Now for my experience. About four years ago, in the early spring, I launched my 21 foot boat in the Hudson River. I had a tough time starting the engine and when I finally got it started, it ran really roughly. When I checked out the voltage, RPM, and tilt gauges, each was pegged in the maximum position. I knew we had a really close lightning strike (I'll get to that), and I figured it must have struck near the boat which I kept on a corner of my property. We cruised the river for about an hour and then stopped for lunch. We anchored our boat and tied up along side of my friend's boat. After about a half hour, my friend mentioned that my boat looked like it was sitting low in the water. I pulled off the back cover and discovered that I had about 400 gallons of water in the bilge. I WAS SINKING! We quickly started the engine, and headed for shore. As we did, we pulled the drain plug to drain some of the water from the boat.

When I got home, I closely inspected the boat and discovered that it had been directly hit by lightning. The bolt apparently hit the engine, burned a hole through the metal casing, then traveled through the transom, and burned its way through the bottom. In doing so, it left two 1 inch holes in the bottom of the boat. I also discovered that all my gauges were destroyed, some of the boat wiring was completely melted, and the engine ignition system was partially destroyed.

As if that wasn't bad enough, I parked my boat in an area of my yard that is directly over the underground electrical service to my house. After the bolt punched a hole in the bottom of my boat, it traveled into my house where it blew up my well pump controller, totaled my water softener, ruined my answering machine, fried my stereo, burned out an outlet, and blew a 3 inch wide hole in my concrete basement floor (don't ask how because I am still trying to figure that one out). All said, well over $3,000 worth of damage!

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Stratocumulus Clouds from Above

Even though they sometimes look as if you could walk on them, clouds are actually a collection of billions of tiny water droplets, ice crystals, or mixtures of both. As air rises into the upper atmosphere, it cools. When this happens, the water vapor that is present in the air reaches saturation and begins to form very small droplets. The droplets begin to slowly fall. As they reach the lower part of the cloud they evaporate. Therefore a cloud is a continuous cycle of droplets falling and then evaporating. Clouds are classified according to their appearance and height. Let's start from the ground and work our way up.

Low Clouds: Cumulonimbus

Low clouds occur from ground level up to 6,500 feet (2,000 meters). Cumulonimbus , or storm clouds, generally have flat bases and rounded domes . Cumulus clouds vary in size from the small puffball-like clouds to huge dome-clouds that often develop into thunderclouds. Stratus clouds are usually dark shapeless clouds that appear as streaks across the sky or as gray layers hanging above the Earth. Stratocumulus clouds are large, round and lumpy and usually cover the entire sky.

Mid-level Clouds: Nimbostratus

Mid-level clouds occur from 6,500 to 23,000 feet (2,000 to 7,000 meters). Nimbostratus clouds are thick, dark, and shapeless and usually bring rain or snow. Altostratus clouds usually cover the sky with a partially transparent layer that you may see the sun through (as a bright spot). Altocumulus clouds appear as large rounded puffy clouds.

High Clouds: Cirrostratus

High clouds occur from 16,500 to 45,000 feet (5,000 to 13,700 meters). Cirrostratus clouds often look like tangled webs or thin whitish sheets. When they cover the sky, you may see a large ring or around the sun or moon which is caused by the bending of light rays as they pass through the ice particles in the clouds. Cirrocumulus clouds look like very small round balls or flakes. Cirrus clouds are white and look like bands of feathers.

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The Wind

Some days it is perfectly still. Other days it will turn your umbrella inside out, blow shingles off your roof, and push your car all over the road. The power of the wind is amazing. A few years ago we visited Jockey's Ridge park in the Outer Banks of North Carolina. Jockey's Ridge is a gigantic sand dune system that is continually reshaped by the wind. There is actually a miniature golf course that lies buried under the sand as a result of the relentless wind. What causes the wind to blow and behave in this manner?

Airborne off a 100 foot (30.5 meters)
sand dune at Jockey's Ridge

All wind is caused by differences in the temperature of the atmosphere and by the rotation of the Earth. Have you ever noticed at the beach on a nice day that the wind usually blows on-shore during the day and off-shore during the evening? This is a perfect example of the effect of temperature differences.

The sun heats land and water differently. Oceans and lakes absorb much of the heat energy from the sun and the air above them tends to be relatively cool. The land, however, absorbs much less heat than water, and as a result the air above it is heated more. Hence the air over land tends to be warmer than the air over the water.

The warmer air over the land expands and becomes lighter. This creates a low pressure situation. The air over water is cooler and denser (heavier), than the land air and this creates a high pressure situation. The high pressure air over the water pushes into the low pressure area on the land. The air moving in from the water toward the land pushes the lighter land air up and out of its way. This movement is what causes a sea breeze.

When night comes the opposite occurs because the air over the land cools more rapidly than the air over the sea. This causes the breeze to blow out to sea during the night.

All winds near the Earth's surface are caused by differences in atmospheric pressure brought about by uneven heating. Air moves from regions where pressure is high toward regions where pressure is low. Generally, the larger the difference between the low and high pressure areas, the harder the wind blows. This is why there is often very strong wind when a cold or warm front moves into an area.

Differences in temperature and pressure are also responsible for large scale winds called planetary winds. The huge difference between the heated air in the tropics and the cold air in the polar regions is a primary contributor to planetary winds.

In the area of the equator, there is a low pressure area called the doldrums (see diagram below). This is an area of relatively calm weather. Here the air rises upward from the surface of the earth and toward the poles.

Planetary Winds - L = low pressure area,
H=high pressure area

The high pressure air that moves into the equator area creates winds that are known as the Northeast Trade winds . The trade winds do not blow directly toward the equator. They are deflected by the Earth's rotation.

Beyond the regions of the trade winds, there are two other calm areas (at about 35 degrees north and 30 degrees south latitude) known as the Horse Latitudes. The air which moves upward at the equator settles down to the Earth in these areas. Since the air settles nearly straight down in this region, there is little wind and a high pressure area.

Some of the air which settles into the horse latitudes goes back immediately into the trade winds. The rest moves toward the poles to form the Prevailing Westerlies . The polar regions tend to send strong winds toward the equator. These winds are called the Polar Easterlies.

Cyclonic storms frequently are formed where the Prevailing Westerlies meet the Polar Easterlies and where the Northeast Trade Winds collide.

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Meteorology Lingo

Here is some Meteorology Lingo that will blow your friends away (no pun intended)!

A device used to measure wind speed.

The height of the lowest cloud layer.

A device used to measure the height of clouds.

The process of cyclone development.

An increase in temperature with height. This is the opposite of what usually occurs.

A device used to measure humidity.

Tropical Depression
An intense tropical cyclone.

Falling precipitation that evaporates before it reaches the surface of the Earth.

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Weather Extremes

We have all experienced extreme weather at one time or another: a violent storm, a hot day, strong winds, etc. However, the extremes that I will discuss below are ones that we would all be glad to miss out on.

Highest Temperature
The highest temperature ever recorded was 136 F (57.8 C) at Al'Aziziyah, Libya on September 13, 1922. This was in the shade!

Lowest Temperature
The lowest temperature ever recorded was -128.6 F (-89.2 C) at Vostok, Antarctica on July 21, 1983.

Most Rainfall in 24 Hours
73.62 inches (187 cm) of rain fell in 24 hours in Cilaos, Reunion, Indian Ocean on March 15, 1952.

Most Rainfall in a Year
1041.8 inches (2646 cm) of rain fell between August 1, 1860 and July 31,1861 at Cherrapunji, Meghalaya, India.

Greatest Snowfall for a Single Storm
189 inches (480 cm) of snow fell during a storm at Mount Shasta Ski Bowl, CA, USA on February 13-19, 1959 .

Greatest Snowfall in a Year
1,224.5 inches (3110 cm) of snow fell over a one year period (February 19, 1971 to February 18, 1972) at Paradise, Mount Rainier, WA, USA.

Highest Wind Speed
A wind speed of 231 miles per hour (371.7 kilometer per hour)was recorded at Mount Washington, NH, USA on April 12, 1934.

Largest Hailstones
Huge hailstones weighing 2.25 pounds (1.02 kilograms) each killed 92 people in the Gopalganj district of Bangladesh on April 14, 1986.

Deadliest Flood
More than 2000 people died in a flood in Johnstown, PA (USA) on May 31, 1889. The water formed a wall 20-30 feet (6.1 - 9.1 meters) high.

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