HurricanesHurricanesOne of Natures most powerful and destructive storms

Hurricanes are known by many names around the world

Cyclones in the Indian Ocean

Typhoons in the Western Pacific

Hurricanes in the Atlantic and east Pacific

Hurricane SeasonSince hurricanes need warm ocean waters they form during the warmer months. So, hurricane season

begins on June 1st and

ends November 30.

Recipe for a HurricaneIngredients:Warm water. Warmer than 26.5 0C (810F)

High Relative Humidity. This reduces the amount of evaporation in clouds and maximizes the amount of heat released because there is more precipitation. (water vapor releases heat when it condenses or changes to precipitation). The concentration of heat is critical to driving the system.

Low vertical wind shear. This means that the wind speed does not change with altitude. This allows the storm to grow vertically concentrating the heat released from precipitation in a smaller vertical area. High vertical wind shear would cause the storm to grow over a larger area.Converging winds (winds blowing towards each other)

ProcedureFirst: Start a convection process. The warm ocean waters warm the air above it causing it to rise lifting moisture with it This starts the convection process.

The red arrows show warm air rising and the blue arrows show cooler air sinking.

Second: Add converging winds. These create a cyclone, or low pressure area, increasing convection. Click on this link to see how convergence aids in building a hurricane. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/grow/cisk.rxml

.

The pink arrows are the converging winds. The red arrows are warm air rising. The blue arrows are cool air sinking.

Fourth: Add low vertical wind shear. This will keep the building storm more upright allowing the energy being created from being spread out over a large area. Click on the link below to see an animation.

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/grow/home.rxml

Third: Create a high pressure area aloft. This is done by the release of heat as the water vapor cools and condenses as it rises. The heated air aloft expands and creates the high pressure area

Fifth: Wait and watch.

The low pressure at the surface and the high pressure aloft creates a “pressure gradient”. This increases the rising motion and the release of heat aloft as condensation occurs. If these conditions continue the storm builds upon itself and a hurricane is made.

Stages of Hurricane DevelopmentHurricanes evolve through a life cycle of stages from birth to death.

The birth of a hurricane, having only a

slight circulation with no closed isobars

around an area of low pressure.

Tropical disturbances commonly exist in

the tropical trade winds at any one time

and are often accompanied by clouds and precipitation.

Stage one: Tropical Disturbance

Stage two: Tropical DepressionIf sustained winds increase to at least 23 miles per hour, a disturbance is upgraded to a tropical depression. Surface wind speeds vary between 23 miles per hour and 38 miles per hour and a tropical depression has at least one closed isobar that accompanies a drop in pressure in the center of the storm.

Stage three: Tropical Storm

If sustained wind speeds increase to at least 39 miles per hour, a tropical depression is upgraded to a tropical storm. Surface wind speeds vary between 39 miles per hour and 73 miles per hour and the storm becomes more organized. Tropical storms resemble the appearance of hurricanes due to the intensified circulation.

Stage four: H U R R I C A N EAs surface pressures continue to drop, a tropical storm becomes a hurricane when sustained wind speeds exceed 74 miles per hour. A pronounced rotation develops around the central core as spiral rain bands rotate around the eye of the storm. The heaviest precipitation and strongest winds are associated with the eye wall. Click on this link to see an animation of how a hurricane forms http://observe.arc.nasa.gov/nasa/earth/hurricane/creation.html

Hurricane AnatomyThe eye is found at the center and are between 20-50km in diameter. The eye is the focus of the hurricane, the point about which the rest of the storm rotates and where the lowest surface pressures are found in the storm.

Skies are often clear above the eye and winds are relatively light. It is actually the calmest section of any hurricane.

Click on this link to watch an animation and explanation of the formation of the eye

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/stages/cane/eye.rxml

The Eye Wall

Located just outside of the eye is the eye wall. This is the location within a hurricane where the most damaging winds and intense rainfall is found

Spiral Bands

Radiating outward from the eye wall one can see a banded structure within the clouds. These clouds are called either spiral rain bands (or spiral bands).

There are sometimes gaps in between these bands where no rain is found. In fact, if one were to travel between the outer edge of the hurricane to its center, one would normally progress from light rain to dry, back to slightly more intense rain again over and over with each period of rainfall being more intense and lasting longer until reaching the eye.

Movement of Hurricanes(Steered by Global Winds)

Hurricane Strength

 

Category

Wind Speeds

mi/hr

Storm Surge

feet

ObservedDamage

1 74-95  

4-5  

some damage to trees, shrubbery, and unanchored mobile homes

2 96-110  

6-8  

major damage to mobile homes; damage buildings' roofs, and blow trees down

3 111-130  

9-12  

destroy mobile homes; blow down large trees; damage small buildings

4 131-155  

13-18  

completely destroy mobile homes; lower floors of structures near shore are susceptible to flooding

5 >"155"  

>"18"  

extensive damage to homes and industrial buildings; blow away small buildings; lower floors of structures within 500 meters of shore and less than 4.5 m (15 ft) above sea level are damaged

 

Saffir-Simpson Hurricane Damage-Potential Scale

Damage Caused By HurricanesWinds http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/damg/wind.rxml

Storm Surge http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/damg/surg.rxml

Heavy Rain and Flooding

Tornadoes

Rip Tides http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/damg/rip.rxml

Public Awarness

2005 Hurricane Season