Ch. 11: Hurricanes

Be able to…

Define what hurricane is.

Identify the life and death of a hurricane.

Identify the ways we track hurricanes.

What are Hurricanes?

• Smaller than mid-latitude

cyclones.

• Don’t have warm and cold fronts.

• Most destructive storms on earth.

What/ Where are Hurricanes?

A hurricane is an intense tropical low-pressure area with sustained winds of 74mph or greater.

They circulate counter-clockwise about their centers in the Northern Hemisphere.

Most Hurricanes form between the latitudes of 5°and 20°

Who’s # 1

• North Pacific has the greatest number of storms.– average 20 per year

• U.S. Only averages 11 tropical storms, and 6 hurricanes in the Atlantic Ocean.

Hurricane Data

• 4 methods of gathering data on hurricanes1. Satellite

2. Reconnaissance aircraft

3. Radar

4. Data buoys

← Best Method

Hurricane Destruction

• Hurricanes cause damage three ways:

1. Strong winds

2. Heavy rains

3. Storm Surge

The greatest damage associated

with hurricanes is caused by?

Storm surges

Storm Tide Facts

• Hurricane Camille in 1969 produced a 24-foot storm tide in Mississippi.

• Hurricane Hugo in 1989 generated a 20-foot storm tide in South Carolina.

• Hurricane Katrina in 2005 generated a 27-foot storm tide in Mississippi.

Hurricane Season

Hurricane Season

North American hurricane season is normally from June to November.

The most active months in the Atlantic are: Aug. – Oct.

The three Category 5 storms to hit the USA:

1. 1935 Florida Keys "Labor Day" hurricane.

2. Hurricane Camille, which hit Mississippi in 1969.

3. Hurricane Andrew, which hit Florida, on Aug. 24, 1992.

Birth of a Hurricane

• Hurricanes are formed from complex of thunderstorms. • The ocean water itself must be warmer than 80°F. • The heat and moisture from this warm water is ultimately

the source of energy for hurricanes.

Death of a Hurricane• Hurricanes will weaken

rapidly when they:– travel over land

– travel over colder ocean waters

– locations with insufficient heat and/or moisture.

Wind Shear

• Wind shear is defined as the amount of change in the wind's direction or speed with increasing altitude. – Weak wind shear is good for tropical storm

development.– Strong wind shear is bad for tropical storm development.

Hurricane Life Cycle

1) Tropical Disturbance or Wave

• Most common, about 100 forming each season.

• They lack a closed circulation

• Wind speeds are less than 20 knots, or 25 mph.

Hurricane Life Cycle

2) Tropical Depression

• A wave becomes a depression when there is a presence of a closed circulation, and sustained winds are 20 knots, or 25 mph.

• At this point, the system is still quite disorganized.

Hurricane Life Cycle

3) Tropical Storm

A depression becomes a tropical storm when thunderstorm activity moves over the closed circulation, and sustained winds reach at least 35 knots, or 39 mph.

At this point, the system is capable of causing minimal damage, and the storm receives a name.

Example. - T.S. Katrina)

Hurricane Life Cycle4) Hurricane

A tropical storm becomes a hurricane when the closed circulation becomes an eye, and sustained winds reach at least 65 knots, or 74 mph.

At this point, the system is capable of causing significant damage.

* Sustained winds

A 1-minute average wind measured at

about 33 ft (10 meters) above the

surface.

Life Cycle of a Hurricane

Other Names for Hurricanes

• Hurricane is given to systems that develop over the Atlantic or the eastern Pacific Oceans.

• Typhoons in the western North Pacific and Philippines

• Cyclones in the Indian and South Pacific Ocean

Saffir-Simpson Hurricane Scale• A Category 1 storm has the lowest wind speeds, while

a Category 5 hurricane has the strongest.

• The maximum sustained surface wind speed (peak 1-minute wind at 33 feet/10 meters) is the determining factor in the scale.

The Worst U.S Hurricanes• Most Damage

– Hurricane Katrina, August 2005, was the costliest

hurricane in history, racking up more than $80 billion

in damages. (#2 Hurricane Andrew, 1992 - $ 26 billion)

• Deadliest

– Galveston Hurricane 1900, 8,000 deaths attributed to

the storm.

• Strongest

– Hurricane Camille, which hit Mississippi with winds at

190 mph in 1969.

– The 882 mb pressure reported in Hurricane Wilma in

2005 is the lowest central pressure on record in an

Atlantic hurricane

Hurricane Watch vs. Warning

• HURRICANE WATCH: Hurricane conditions

are possible. The hurricane watch is issued 48 hours in

advance of the anticipated onset of tropical-storm-force

winds.

• HURRICANE WARNING: Hurricane

conditions are expected. The hurricane warning is issued

36 hours in advance of the anticipated onset of tropical-

storm-force winds.