SEVERE WEATHER

What is a HURRICANE?

*A large, swirling low-pressure tropical weather system that has wind speeds of at least 119 km/h.

*Most powerful storm

*Can travel for thousands of kilometers

*Vary in size from 160-1500km in diameter

*Atlantic/Eastern Pacific Oceans = hurricane

*Western Pacific = typhoon

*Indian Ocean = cyclone

Different names…same disaster

How do they form?*Begins as thunderstorms over warm ocean water

*Heat = energy, so rising warm air provides the energy to create the hurricane

*Air masses meet and begin to spin because of the Coriolis Effect

-Clockwise in the Northern Hemisphere

-Counter-clockwise in the Southern Hemisphere

Progression of a hurricane

*Tropical Depression-

winds of less than 62 km/h

*Tropical Storm-

winds of 62 km/h-118km/h

*Hurricane-

winds of at least 119 km/h

Parts of a hurricane*Eye- calmest area, VERY low pressure, can be very wide, be careful not to mistake for the end of a hurricane

*Wall- most deadly area of a hurricane, wall of clouds that surrounds the eye, also called eye wall

*Spiral Bands- largest area of hurricane, where rain falls from, thin clouds surrounding the eye wall

When do they occur?*June 1 to November 30 is known as hurricane season

What is a storm surge?

How are they measured?Saffir-Simpson Hurricane Scale

Category Wind Speed Effects

174 to 95 mph(119 to 153 kph)

-Storm surge 4 to 5 ft (1.2 to 1.5 m) above normal•Some flooding•Little or no structural damage

296 to 110 mph(155 to 177 kph)

-Storm surge 6 to 8 ft (1.8 to 2.4 m) above normal•Trees down•Roof damage (shingles ripped off)

3111 to 130 mph(178.6 to 209 kph)

-Storm surge 9 to 12 ft (2.7 to 3.7 m) above normal•Structural damage in houses•Mobile homes destroyed•Severe flooding

4131 to 154 mph(210 to 247.8 kph)

-Storm surge 13 to 18 ft (4 to 5.5 m) above normal•Severe flooding inland•Some roofs ripped off•Major structural damage

5>155 mph(> 249.4 kph)

-Storm surge at least 18 ft (5.5 m) above normal•Severe flooding further inland•Serious damage to most wooden structures

What’s in a name?

*There are different hurricane names depending on where the hurricane occurs.

*Hurricane names are retired when they have made extremely negative economic and social impacts.

*Sets of names are repeated after a number of years.

*Go to the National Hurricane Center website for more details

What is a tornado?*A violent, whirling wind that moves in a narrow path over land.

*Can last for hours and travel hundreds of miles if very powerful; 160 km/h to 480 km/h

When do they occur?*Spring time

*Most commonly in the USA (“Tornado Alley”)

How do they form?*Begins with a thunderstorm

*Any change in the state of matter (example: gas liquid, condensation) results in heat, which is a form of energy

*Rising warm air creates a thunderstorm…we call this rising air an UPDRAFT

*Differences in wind direction and speed near Earth’s surface cause a funnel/vortex parallel to Earth’s surface, the updrafts from a storm can turn that funnel/vortex upward to create a column of rising air.

*This column of rising air becomes a vortex, and when the vortex goes from the ground to the bottom of the cloud, it becomes a tornado

*Funnel cloud = the column of air does not reach the ground

How are they measured?Enhanced Fujita Scale, named for its inventor, University of Chicago meteorologist Theodore Fujita. Fujita created the scale, based on the wind speed and type of damage caused by a tornado, in 1971. There were six levels on the original scale:

LevelWind

SpeedPossible Damage

F040 - 72 mph

Light damage: Tears branches from trees; rips shallow-rooted trees from the ground; can damage sign-posts, traffic signals and chimneys

F173 - 112 mph

Moderate damage: Roofing materials and vinyl siding can be displaced; mobile homes are highly vulnerable and can easily be knocked from the foundation or toppled; motorists can be sent careening off road and possibly flipped over

F2113 - 157 mph

Considerable damage: Well established trees are easily uprooted; mobile homes are dessimated; entire roofs can be ripped off houses; train cars and trucking hauls are knocked over; small objects become dangerous missiles

F3158 - 206 mph

Severe damage: Forests are destroyed as a majority of trees are ripped from the ground; entire trains are derailed and knocked over; walls and roofs are torn from houses

F4207 - 260 mph

Devastating damage: Houses and other small structures can be razed entirely; automobiles are propelled through the air.

F5261 - 318 mph

Incredible damage: Cars become projectiles as they are hurled through the air; entire houses are completely destroyed after being ripped from the foundation and sent tumbling into the distance; steel-reinforced concrete structures can be seriously damage

THunderstorms• Small, intense weather systems that

produce strong winds, heavy rain, lightning and thunder.

• Usually occur along cold fronts, can occur elsewhere also.

• Must have two conditions

1. Warm, moist air near Earth’s surface

2. Unstable atmosphere