This work is supported by a National Science Foundation (NSF) collaboration between the Directorates for Education and Human Resources (EHR) and Geociences (GEO) under grant DUE - 1125331

Hurricane Formation:Ocean and Atmosphere Systems

Interact to Create Hurricanes

Questions

• What is a hurricane?• What four conditions are necessary for hurricane formation?• What happens as hurricanes approach land?

What is a Hurricane?

• Make a list of hurricane characteristics:

What is a Hurricane?

• Formal definition:An intense low pressure system with sustained winds >74 mph

What Makes a Hurricane?

• Four essential ingredients

What Makes a Hurricane?1) Warm SST >26.5°C (80°F) over large area

What Makes a Hurricane?

1) Warm SST (>26.5 C) over large area2) Instability in atmosphere (rising air mass, beneath which surface

winds converge)

What Makes a Hurricane?

1) Warm SST (>26.5 C) over large area2) Instability in atmosphere (rising air mass)3) Little/no vertical wind shear through atmosphere to tropopause

(ocean)

(atmosphere)

(tropopause)

Which wind profile has too much vertical shear for hurricanes to form?

What Makes a Hurricane?

1) Warm SST (>26.5 C) over large area

2) Instability in atmosphere (rising air mass)

3) Little/no vertical wind shear through troposphere

4) Sufficient latitude >5-10o off equator

Hurricanes are powered by:

• latent heat stored in water vapor– released when water condenses

1. Warm water supplies sensible heat and humidity to overlying air

2. Air decreases density; rises

3. Air cools; H2Ovapor condenses

4. Latent heat released-- Heat warms air; rises faster

5. P gradient increases -- Faster winds converge at the low pressure center

-- More water vapor into system!

Feedback between the ocean and atmosphere systems!

Can Hurricanes Cross the Equator?

• Discuss with the person next to you. • Why or why not?

Can Hurricanes Cross the Equator?

– Discuss with the person next to you. – Why or why not?

(Hurricane tracks 1985-2005; NASA)

North Atlantic Hurricane Season is June-November

Most storms occur in which month?

January

Febru

ary

Marc

hApril

May

June

July

August

September

October

November

December

0

0.5

1

1.5

2

2.5

3

3.5

4

Tropical StormsHurricanesHurricanes w/US Landfall

Ave

rage

num

ber p

er m

onth

, 185

1-20

11

Which of these things would cause a hurricane to lose energy?

a) Moving over colder waterb) Moving over warmer waterc) Making landfalld) Crossing the ocean

As a hurricane approaches land

Wind and Rain

(NOAA)

Storm Surge

(NASA)

As hurricanes make landfall, they decrease in strength

Why?

Remember what fuels hurricanes…

Warm water!

Draw:

• The relationships between the ocean, atmosphere, and people in a hurricane.

Make sure you can now answer these:What is a hurricane?

- What four conditions are necessary for hurricane formation?

- What happens as hurricanes approach land?

References• Slides 4 and 5. Public Domain Image of Hurricane Rita as a Category 5 hurricane. http

://www.nnvl.noaa.gov/hurseas2005/Rita2045zD-050921-1kg12.jpg• Slide 6. Public Domain Image of SST. http

://www.osdpd.noaa.gov/data/sst/fields/FS_km10000.gif• Slide 7. Public Domain illustration of tropical waves. http://www.aoml.noaa.gov/hrd/tcfaq/

Twaves.jpg• Slide 9. Creative Commons illustration of hurricane forces: http://en.wikipedia.org/wiki/

File:Hurricane_isabel_and_coriolis_force.jpg• Slide 12. Public Domain image of hurricane tracks: http://www.nasa.gov/images/content/

313775main_global_hurr_tracks_HI.jpg• Slide 15. Public Domain image of Hurricane Eloise approaching shore.http

://www.photolib.noaa.gov/historic/nws/images/big/wea00416.jpg• Slide 17. Public Domain illustration of storm surge.http

://earthobservatory.nasa.gov/Library/Hurricanes/Images/storm_surge.gif• Slide 18. Public Domain image of 2012 hurricane tracks. http://www.nhc.noaa.gov/

2012atlan.shtml• All other illustrations and text were created by Lisa Gilbert under a Creative Commons Attribution-NonCommercial-

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