Geo Science 102 Hurricanes

What is a hurricane?

A hurricane is an intense tropical cyclone with strong rotating winds around a low-pressure center.

What is a tropical cyclone?

A tropical cyclone is a storm system with rotating winds around low pressure that forms over warm tropical oceans

What does “cyclone” mean?

It means winds rotate around a low-pressure center.

What does “tropical” mean?

It means the storm forms in warm tropical regions.

Why do tropical cyclones have different names depending on the ocean basin?

Because different regions use different naming systems (e.g., hurricanes, typhoons, cyclones).

How do tropical cyclones form? (Step 1)

Warm ocean water heats the air above it, causing the air to rise and form clouds.

How do tropical cyclones form? (Step 2)

As air rises, low pressure develops, causing surrounding air to move in and begin rotating.

How do tropical cyclones form? (Step 3)

More clouds form and release heat, lowering pressure further and strengthening winds.

What causes air to rise over warm ocean water?

Warm water heats the air, making it less dense so it rises.

What causes low pressure to develop in a storm?

Rising air removes mass from the surface, creating a low-pressure area.

Why do winds begin to rotate in a cyclone?

Because of the Coriolis Effect acting on moving air.

Why do winds intensify as more clouds form?

Because heat released from cloud formation fuels the storm and lowers pressure further.

Which is denser and heavier: warm, humid air or cold, dry air?

Cold, dry air is denser and heavier.

Why is cold, dry air denser than warm, humid air?

Because colder air molecules move less and are packed closer together.

In the Northern Hemisphere, where is storm surge highest in a hurricane?

In the forward right quadrant of the storm.

Why is storm surge highest in the forward right quadrant of a storm?

Because storm motion and wind rotation combine, producing the strongest onshore winds.

Why are winds stronger on the right side of a hurricane (Northern Hemisphere)?

Because the storm’s forward motion adds to the rotational wind speed on that side.

Why is New Orleans especially vulnerable to flooding?

Because about 70% of the city lies below sea level.

What percentage of New Orleans lies below sea level?

About 70%.

What are levees and what is their purpose?

Levees are barriers that keep water from flooding land.

How do drainage canals and pumps help prevent flooding?

They remove rainwater and excess water from low-lying areas.

What is the Coriolis Effect?

The apparent deflection of moving objects due to Earth’s rotation.

Where is the Coriolis Effect strongest?

At the poles.

Where is the Coriolis Effect weakest?

At the equator (zero).

Why is the Coriolis Effect zero at the equator?

Because there is no lateral deflection at 0° latitude.

How does Earth’s rotation speed vary with latitude?

It is fastest at the equator and slowest at the poles.

Why does the Coriolis Effect affect moving objects?

Because Earth rotates, causing paths of motion to curve relative to the surface.

Why does the Coriolis Effect matter for hurricanes?

It causes storms to rotate and determines their direction of spin.

What makes tropical cyclones difficult to study globally?

They are rare, small-scale events and cannot be fully resolved by global climate models.

About how many tropical cyclones occur globally each year?

About 80 per year on average.

Why is there no clear theory for cyclone frequency?

Because of large variability (year-to-year and long-term) and complex interactions.

How does El Niño affect Atlantic hurricanes?

El Niño years typically have fewer Atlantic hurricanes.

Why is the observational record for hurricanes relatively short?

Because full global coverage (via satellites) only began in the 1970s.

Why were hurricanes often missed before satellites?

There were limited observations over open oceans.

How did scientists estimate past hurricane activity before satellites?

Using ship track data to estimate storms that may have been missed.

Is there a clear long-term trend in total hurricane frequency?

No, there is no clear long-term trend.

What type of variability dominates hurricane records?

Interannual (year-to-year) variability.

What happened in the 2005 Atlantic hurricane season?

There was a record of 15 hurricanes, including Katrina and Wilma.

What trend appears after smoothing hurricane data?

An increase since ~1980, but still comparable to late 1800s levels.

What are “major hurricanes”?

Category 3–5 storms.

Why did major hurricane frequency drop in the 1970s–1980s?

Cooling from aerosols and other factors reduced storm intensity.

What role did aerosols play in hurricane trends?

What factors increase hurricane activity?

Warmer sea surface temperatures (from greenhouse warming)

Has global warming clearly increased hurricane frequency since 1860?

No, there is no clear impact on frequency.

Why is the climate signal hard to detect in hurricanes?

It is masked by natural variability and aerosol effects.

What do models predict about future hurricane frequency?

A decrease in total number of storms

What do models predict about hurricane intensity?

An increase in intensity per storm.

What do models predict about strong hurricanes (Cat 4–5)?

They will become more frequent.

What do models predict about hurricane rainfall?

Rainfall rates will increase

Why is hurricane frequency expected to decrease?

Due to increased wind shear.

Why is hurricane intensity expected to increase?

Because of warmer sea surface temperatures.

By how much are Category 4–5 storms projected to increase?

About 28% increase.

Where will rainfall increase the most in storms?

Near the center (eyewall).

What has the IPCC concluded about strong hurricanes?

The proportion of Category 3–5 storms has likely increased globally.

What has the IPCC concluded about rapid intensification?

It has likely increased over the past 40 years.

How has climate change affected Hurricane Harvey?

It contributed to extreme rainfall amounts.

What are the impacts of Hurricane Harvey?

~90 deaths, ~200,000 homes damaged, ~$160 billion in costs.

What were the impacts of Hurricane Katrina?

~1361 deaths, massive displacement, ~$200 billion in damages.

How did Katrina affect New Orleans population?

Dropped from ~485,000 to ~230,000, later recovering to ~400,000.

Are hurricane landfall patterns certain under climate change?

No, they are still uncertain and an active research area.

What is an attribution study?

A study that estimates how much climate change influenced a specific event.

How did climate change affect Hurricane Harvey likelihood?

Made extreme rainfall about 6× more likely.

Did climate change increase hurricane intensity in some storms?

Not necessarily; it mainly increased rainfall.

What is the overall conclusion about hurricanes and climate change today?

No clear observed trend in frequency or intensity due to masking effects

What is the main future expectation for hurricanes?

Fewer storms overall, but stronger and wetter ones.

Why will storm surge impacts worsen in the future?

Because sea levels are rising.

Why are hurricanes becoming more costly?

Due to increased coastal development.

Is climate change the main reason hurricanes are more expensive?

No, increased development along coasts is the main reason.

Which of the following are other names for tropical cycles?

-Typhoons

-Hurricanes

 -Typhoons

What provides fuel for tropical cyclone growth?

Warm ocean waters

Which three hurricanes in 2005 were particularly strong and damaging?

Katrina

Wilma

Rita

Where are tropical cyclones extremely rare?

South Atlantic Ocean

What is the Loop Current?

A flow of warm Caribbean water that arcs into and out of the Gulf of Mexico, often boosting hurricanes.

Which location is NOT frequently hit by tropical cyclones?

Brazil

How many people were killed by Hurricane Katrina?

More than 1800

When was the first year in recorded history that the Atlantic basin had 4 Category 5 winds?

2005

Which is stronger: a category 1 hurricane or a category 5 hurricane?

Category 5

What made Superstorm Sandy particularly damaging to New York City?

It had an unusual track that hit NYC straight on, maximizing storm surge

True or False: The idea that melting Arctic sea ice due to global warming is causing a change in midlatitude weather is a well-accepted idea in the scientific community.

False

How can Sandy's damage definitely be attributed to global warming?

Sandy's storm surge was greatly worsened by 11 inches of sea level rise in New York City

True or False: Over the past century, the average number of tropical cyclones worldwide has been increased by global warming

 

False

In the Atlantic basin, tropical cyclones are called:

hurricanes

Tropical cyclones are typically smaller or larger than a typical 1-degree climate model grid?

Smaller

According to most scientific studies, how is the number of tropical cyclones (TCs) expected to change due to global warming?

The number of TCs will decrease

Which particularly damaging hurricane occurred in 1992?

Andrew

True or False: The damage caused by Hurricane Harvey was made worse by global warming

True

Which US territory suffered catastrophic damages from Hurricane Maria?

Puerto Rico

How is the strength of tropical cyclones (TCs) expected to change due to global warming?

TC strength is expected to increase

What is the maximum intensity category for tropical cyclones?

 

5

When is storm surge from a tropical cyclone likely most damaging? 

High tide

Which factors make areas more vulnerable to storm surge?

Wetland loss

Land subsidence

Frequency and intensity of extratropical cyclones in a warming world are: 

Highly uncertain

What are hurricane ratings systems based on?

Maximum sustained wind speed

What are three things that fuel or power a Hurricane?

Warm sea surface temperatures, low atmospheric pressure, and humid air

The surface air pressure in the eye of a hurricane is_______:

low, due to the warm, rising moist air that surrounds it.

Why is there a lack of tropical cyclones in the northern Pacific (off western U.S. and Canadian coastline) and the Southern Ocean near Antarctica?

The surface ocean temperatures are too cold in these regions.