Hurricane Formation:
Ocean and Atmosphere Systems
Interact to Create Hurricanes
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
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 area
2) Instability in atmosphere (rising air mass, beneath which surface
winds converge)
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 atmosphere to tropopause
(tropopause)
Which wind profile has
too much vertical shear
for hurricanes to form?
(atmosphere)
(ocean)
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
Feedback
3. Air cools; H2Ovapor condenses
between the
4. Latent heat released
ocean and
-- Heat warms air; rises faster
5. P gradient increases
-- Faster winds converge at the low pressure center
-- More water vapor into system!
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?
Average number per month, 18512011
4
3.5
3
2.5
2
1.5
1
0.5
0
Tropical Storms
Hurricanes
Hurricanes w/US Landfall
Which of these things would cause
a hurricane to lose energy?
a)
b)
c)
d)
Moving over colder water
Moving over warmer water
Making landfall
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
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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-NonCommercialShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial
purposes as long as you provide attribution and offer any derivative works under a similar license.