HURRICANES!…AN OVERVIEW OF TROPICAL CYCLONES

What is a hurricane?A hurricane is an intense rotating storm that forms over the tropical oceans.

•“Hurricane” is a specific regional name. • In general, these storms are known as “tropical cyclones”:

• Tropical depression: winds < 39 mph• Tropical storm: winds < 74 mph•Hurricane: winds > 74 mph

- Atlantic and Eastern Pacific Oceans (hurricanes)- Western North Pacific Ocean (typhoons)- South Pacific and Indian Oceans (cyclones)

Where do tropical cyclones form?

(10)(26)

(14)(15)

(5)

(9)

(nn) Number of storms per year

Why are the winds so strong in a hurricane?

Winds always move from areas of higher pressure to areas of lower pressure. The bigger the difference between the high and low pressure, the stronger the winds.

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The winds from Hurricane Fabian battering Bermuda on September 5, 2003.

What causes the winds to rotate around a hurricane?

Hurricane Isabel making landfall on September 18, 2003

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The Coriolis Effect: A change in the direction of moving objects due to

those objects moving on a rotating, spherical planet.

The Coriolis Effect caused by Earth’s rotation.

How is a lawn mower like a hurricane?

Gas provides the fuel for the mower’s engine

The engine uses the fuel to perform work and move the grass-cutting

blade

The starter rope and spark plug

are the “triggers” for making the mower start

Exhaust fumes are expelled

out away from the engine

The hurricane heat engine: how it works3. Having lost most of its heat and energy, the air is now expelled outward away from the center of the storm in the cooler hurricane outflow at high levels.

In mature hurricanes, an eye forms in the center. Here, the air is descending and the region is generally cloud-free.

2. The warm, moist air rises in thunderstorms surrounding the eye, supplying the fuel that helps strengthen the storm and intensify the winds.

1. As air rushes into the hurricane’s low pressure center, the air picks up heat and moisture (fuel) from the warm ocean surface.

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Hurricane formation

• Hurricanes grow from clusters of smaller storms and become more organized and intense as they develop.

Daily images of Hurricane

Frances (2004), from a weak

tropical depression to a

Category-4 hurricane… to

landfall

Hurricanes don’t just form out of thin air. They typically grow from clusters of smaller thunderstorms that move across the oceans.

The triple threat of damage from a hurricane:• Wind Damage: Wind gusts can approach 200

mph in the strongest hurricanes.

• Storm Surge: The winds of a hurricane pile up ocean water that can inundate coastlines with water levels up to 30 feet higher than normal.

• Inland Flooding: Today, this is the greatest risk to life from a hurricane. Hurricanes and tropical storms, especially slow-moving ones, can drop huge amounts of rain in a very short time, even inland far from where the storm made landfall. From 1970-2000, 9 out of every 10 fatalities in tropical cyclones were due to drowning from inland flooding.

Wind Damage examples

A 1x4 board of wood was pierced through a palm tree by Hurricane Andrew’s winds in August, 1992.

A mobile home park near Miami, FL was completely destroyed by Hurricane Andrew in August, 1992.

An historic home along the Gulf Coast before and after the passage of Category 5 Hurricane Camille in August, 1969.

The Saffir-Simpson Hurricane Wind Scale: A method for categorizing hurricanes based on wind speed

Category 1

Category 2

Category 3

Category 4 Category 5

Windspeed

(mph)

74-95 96-110 111-130 131-155 >155

Storm surge (ft)

4-5 6-8 9-12 13-18 >18

Damage description

Minimal Moderate Extensive Extreme Catastrophic

Storm Surge examples

Storm surge from Hurricane Carol completely inundates a yacht club in August, 1954.

Apartment building in Pass Christian, Mississippi before and after the passage of Category 5 Hurricane Camille in August, 1969. Thirty-two people ignored warnings and stayed for a “hurricane party”. Only two survived.

Hurricane Katrina’s 30-foot storm surge obliterated every home within several blocks of the shoreline in Pass Christian and Waveland, Mississippi.

Storm Surge examples

Waveland, MS

David & Kimberly King’s house, 4 blocks from the beach, on August 28

(1 day before Katrina hit)

…the same property, same view, on September 2

(4 days after Katrina hit)

•Hurricanes, Tropical Storms, and Tropical Depressions, form over water.•A tropical system is also known as a Cyclone, and a Typhoon.•All Cyclones start as tropical depressions then strengthen to tropical storms, then move on to Hurricane status. •Hurricane strength is measured using the Saffir-Simpson Scale.