OH MY!! !

Hurricanes, Tornadoes, Floods, Droughts, and Fires

When does hurricane season start?

The Atlantic hurricane season is from June 1 to November 30

The Eastern Pacific hurricane season is from May 15 to November 30

Characteristics of a hurricane:

can be up to 600 miles across and have strong winds spiraling inward and upward at speeds of 75 to 200 mph

usually lasts for over a week, moving 10-20 mph over the open ocean

gather heat and energy through contact with warm ocean waters

rotate in a counter-clockwise direction around an ‘eye’

How do hurricanes form?

A hurricane is a system of low pressure that originates over a tropical area.

warm ocean water of 80°F or warmer

rapidly cooling, unstable atmosphere

the wind must be blowing in the same direction and at the same speed to force air upward from the ocean surface

winds flow outward above the storm allowing the air below to rise

hurricanes typically form between 5 to 15 degrees latitude north and south of the equator

Hurricane Formation

Stages of a hurricane:

Stage 1: Tropical Depression: wind speeds of less than 38 miles per hour

Stage 2: Tropical Storm: wind speeds of 39 mph to 73 mph

Stage 3: Hurricane: wind speeds greater than 74 mph

Saffir-Simpson Scale

•The Saffir-Simpson Scale has been updated to only reflect wind speed due to the in-accuracies that air pressure and storm surge represent

•Although the Saffir-Simpson Scale no longer uses pressure and storm surge it is still a vital component of the tracking and forecast process

Tornado ScienceA violently rotating column of air extending

from a thunderstorm cloud to the ground

In the Northern Hemisphere, tornadoes spin counterclockwise

Important to earth’s weather patterns 1. releases pressure that builds up in the atmosphere2. the storms that produce them often bring much needed rain

EF Scale Wind Speed (3 sec. gusts)

Description of Damage

EF0Light Damage

65 – 85 mph Some damage to siding, shingles and gutters; breaks branches from trees

EF1 Moderate Damage

86 – 110 mph Considerable roof damage; uproot trees; damage signs; exterior parts of house

EF2Considerable Damage

111 – 135 mph Damage to mobile homes; roof damage, uproots large trees; damage to cars, flagpoles, signs

EF3Severe Damage

136 – 165 mph Damage to houses, office buildings; ability to toss cars

EF4 Devastating Damage

166 – 200 mph Completely destroys well-built residences, large public buildings, tosses objects like cars

EF5 Incredible Damage

More than 200 mph*to date, no EF5s have been recorded

Significant structural damage to mid- and high-rise buildings; throws cars 100 yards or more

Tornado Formation

Begins with a front – cool air pushes against warm air in the atmosphere, where the two meet is called a front- cool air presses forward, slides underneath the warm air- warm air is pushed upward, water droplets form - thunderheads (fast-growing clouds) form

Tornado Formation

The power of these winds, along with slower winds closer to the ground, can make the rising air start rotating

Air pressure inside the tornadoes funnel is much lower than the air pressure outside which makes it act like a huge vacuum cleaner

The column of spinning winds is called a mesocyclone.

Tornado Formation Model

Tornado Alley

The geography of central US is suitable to bring all necessary ingredients for a tornado together

More than 500 tornadoes typically occur in this area every year

Tornadoes have been reported in every state

Why talk about Floods and Flash Floods?

Floods are among the most frequent and costly natural disasters

Number one killer related to severe weather

Flood Science

Rainfall intensity and duration Prolonged rainfall over several days Intense rainfall over a short time period Ice or debris jam that causes a river to overflow

Topography, soil conditions and ground cover are also important

Can be slow- or fast-rising

Flash Floods

Take only a few minutes to a few hours to develop

Can catch people unpreparedMost occur after intense rainfall, after the

failure of a dam, or following a sudden release of water

What is a drought?

A period of unusually dry weather that persists long enough to cause serious problems such as crop damage and/or water supply shortages.

The severity of the drought depends upon the degree of moisture deficiency, the duration, and the size of the affected area.

How do meteorologists predict droughts?

Monitoring variables such as precipitation and soil moisture

These values are compared to previous data to draw conclusions

Wild Fire Science

Chemical Change: the formation of new material

1. Surface fire - burns along the forest floor (most common)

2. Ground fire – started by lightning, burns along and/or below the forest floor along the dense root systems of trees

3. Crown fire – jumps from treetop to treetop and spreads quickly

Why Wild Fires are Important

Natural part of the ecosystem

Cleans out excess vegetation and insects

Wildlife diversity

Eliminates heavy fuel accumulations

Some plants strengthened by fire

Fire Behavior Triangle

FuelThe dryer and

lighter the fuels the more easily they will ignite.

A continuous layer of fuels on the forest floor can aid in the spread of a fire.

Fire Behavior Triangle

Weather: (wind, temperature and

humidity)Strong winds may

push the flames toward new fuel sources

Winds can transfer embers, sparks or ash to start spot fires

Blowing winds can also dry fuel in moist areas

Fire Behavior Triangle

The temperature of fuel will determine how quickly or slowly fuel reaches its ignition point and burns.

Moisture dampens fuel and slows the spread of flames.

Fire Behavior Triangle

Topography:- Contours, elevation

and slope of an area - Barriers within the

landscape (rocks, cliffs and water) help determine how a fire will spread