Hurricanes are massive rotating storms that transfer heat and energy from the equatorial regions of the globe to the poles. They are formed by warm, moist air and the rotation of the globe.

Hurricanes are possibly one of the most perilous natural hazards known to man, as they have colossal impacts on both humans and the environment in which they live.

Hurricane Bill

Bill is now officially the 1st hurricane of the season with winds reaching over 135mph it has been classified as a category 4 storm. Current predictions of it’s path vary from hitting Bermuda in 3-4 days to missing it entirely and skimming the coast of the mainland USA. The one thing that is for certain is that Bill will certainly cause rip currents and wave swells. It is also possible that due to the favourable weather and sea conditions that Bill will continue to strengthen before making landfall.

Pictured – 19th August

Pictured – 12th August

Tropical Storm Anna:

This was expected to make landfall in the Leeward Islands on Wednesday 19th August, current predictions of the windspeeds make it a tropical depression.

Tropical Storm/Hurricane Felicia:

Hurricane Felicia has been downgraded to a tropical storm, as it winds have reduced from 140mph to around 50mph. It continued to diminish before it made landfall in the Hawaiian island chain as it is continued to move over cooler water. Even though Felicia has been downgraded it is still likely to cause flooding throughout the island chain.

What is a hurricane?

A hurricane is a massive spinning storm with an area of very low pressure at the centre. The average wind-speed in a hurricane is over 140km per hour or 74 mph. The storm can be up to 17km or 10miles high and on average 800km or 500miles wide. It moves forwards at speeds of about 30km per hour or 20mph like a huge spinning top. An average hurricane can travel 500 – 650 km or 300 to 400 miles a day and can travel in total about 5000km or 3000miles before it dies out.

Image via Wikipedia

What conditions are needed for hurricanes to form?

There are specific conditions that need to be met to turn a common storm into a hurricane, the two most important of these are:

• oceans with a surface temperature over 26C, this comes from tropical and provides very warm, moist air.
• Latitudes 5 → 30 which provide the spin or twist due to the rotation of the earth.

For a hurricane to form it is necessary for these trigger conditions to be right at the same time.

Image via Wikipedia

How do hurricanes form?

• The warm sea heats the air above it, as it does this, this moist warm air rises
• This then creates an area of low pressure directly below the rising moist warm air
• Winds rushes in towards this area of low pressure
• These winds then whirl upwards releasing the heat and moisture in them before falling again
• Due to the rotation of the Earth the rising column of air twists
• The column of air eventually begins to look like a cylinder rotating around an area of still air (the eye)
• The rising air cools down producing massive clouds (both cumulus and cumulonimbus clouds)
• At about 10km or 6 miles high, the tops of the clouds are carried outwards, due to the rotating nature of the winds they spread outwards leaving the hurricane’s core cloud free

How does a hurricane get its energy?

Huge amounts of energy are obtained from the warm water when it is evaporated to form the warm, moist air. The energy is then stored in the water vapour that is held in this warm moist air. As the air rises most of this energy is released in the formation of the clouds and rain. As this energy is released it causes another drop in pressure , this means that more air rushes in at an even faster rate to fill this area of low pressure. So more warm, moist air rises from the sea – which then provides more energy for the hurricane. This process is referred to as a self-sustaining heat-engine.

The energy that isn’t used to form clouds is then transferred to the rotating clouds. This small amount of energy (less than 5% of that drawn from the seas) is enough to supply the USA with electricity for about 6months!

Why do they die over land?

These storms can cause widespread destruction, especially when the path of the hurricane is overland. But, a path over land also leads to the hurricane dying. The hurricane’s energy comes from warm seas and the warm moist air it picks up from these, as this energy source is no longer available over land the hurricane runs out of energy. This loss of energy, in combination with the friction cased by travelling over land as opposed to water deforms the air flow of the hurricane. This causes the hurricane’s eye to collapse and fill with cloud, the hurricane then dies.

When do hurricanes occur?

North of the equator these storms occur between July and October. South of the equator they occur between November and March. The name hurricane is used for the storms in the Atlantic, in the Pacific they are called typhoons, finally off Australia and in the Indian Ocean they are referred to as cyclones. The storms are given names starting with ‘A’, ‘B’ etc., In the order they occurred in and the names are alternately male and female.

Other effects:
The most common occurrence linked with hurricanes are strong winds. Other phenomena include:

• Huge waves up to 15 metres high – referred to as hurricane waves that are created by the strong winds and may cause widespread flooding.
• An increase in ocean level – referred to as a swell.
• Rain – hurricanes can pick up roughly 2 billion tons of moisture per day this then forms rain.

Hurricane categories:

Category 1:

• · Wind Speed about 74-95 mph
• · Storm Surge of 4-5 ft.
• · Effects: No real damage to building structures. Damage principally to unanchored mobile homes, shrubbery and trees. Some coastal flooding and minor pier damage.

Category 2:

• · Wind Speed about 96-100 mph
• · Storm Surge of 6-8 ft.
• · Effects: Damage to roofs, windows and doors. Significant damage to mobile homes and vegetation. Coastal flooding may damage piers.

Category 3:

• · Wind Speed about 111-130 mph
• · Storm Surge of 9-12 ft.
• · Effects: Structural damage to small buildings. Destruction of mobile homes and vegetation. Coastal flooding may destroy small structures, larger structures can be damaged by floating debris. Inland flooding may also occur.

Category 4:

• · Wind Speed about 131-155 mph
• · Storm Surge of 13-18 ft.
• · Effects: Structural damage to curtain-walls. Destruction of roofs on small structures. Coastal erosion, particularly of beach areas. Substantial inland flooding may occur.

Category 5:

• · Wind Speed about 156+ mph
• · Storm Surge of 18+ ft.
• · Effects: Structural damage to many buildings, leading to building failure. Destruction of roofs on larger and industrial structures. Coastal erosion, particularly of beach areas. Substantial flooding causes major damage to lower floors of structure near shoreline. Massive evacuation of residential areas near the shoreline occurs.

Hurricane prediction:

The National Hurricane Centre in Miami, Florida looks for potential hurricanes as they are forming, it then tracks them through their life cycle until they dissipate and die. This is done using a network of satellites and many people and computer.

Satellites detect the early stages of development of hurricanes and can help to provide early warning. Specially reinforced aircraft can fly through and over hurricanes to collect additional information. Radar stations can locate and provide more data when the storm is within 200 miles of them. All of this data is then used to forecast the track or path of the storm, to provide residents in the areas that may be affected with the best information possible.

Hurricane warnings

The USA has the most highly developed hurricane warning system. When there are clear-cut signs that a storm may be turning into a hurricane the Weather Bureau system springs into action.

Coastal areas where the winds are expected to reach in excess of 74mph, or dangerously high waves or swells are predicted are issued with a hurricane warning. The general public are usually informed through television broadcasts and a system of flying flags during the day and lanterns at night.

The National Hurricane Center’s website has recently seen development where you type in your zip code to get information about possible hazards in your area and where to evacuate to if it is necessary.

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Lunar Eclipse: August 5-6, 2009

The Perseids Meteor Shower – August 2009

Viewing Venus and The International Space Station on August 17th

Earthquakes: Causes, Effects and Prediction, Including the Recent California Earthquake

Bubonic Plague: Symptoms, Treatment & Transmission