Course: Introduction to Atmospheric sciencesATOC210 by GyuWon LEE

1
Chapter 16 Tropical cyclone (Hurricanes) 
Reading materials Chapters 16 of the text
book The national science digital
library Hurricane Waves

Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
2
Questions 1) What exactly are hurricanes ? 2)
How do they form? 3) Why do they strike the east
coast of North America more frequently than the
west coast?
Objectives 1) Understand the formation and
structure of hurricanes. 2) Understand their
paths and classification.
Approach 1) General concept 2) formation and
structure of hurricanes 3) Paths 4) Outcomes
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
3
General concept Tropical cyclone
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
4
General concept Tropical cyclone
Definition An intense storm of tropical origin,
with sustained winds exceeding 64
kts.
Characteristics - Size 500 km - Eye, eye
wall, spiral rain bands - Very low surface
pressure - Counterclockwise rotation
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
5
How hurricanes form?
Conditions 1) light winds 2) a deep layer of
high humidity (extending up through the
troposphere) 3) Over tropical oceans with
surface temperature greater than 26.5 C over a
vast area (no friction) 4) The Coriolis force
must not be too small (5 to 20 degree
latitude) 5) Trigger
Convergence on the eastern side of a tropical
wave along the ITCZ
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
6
How hurricanes form?
- TSTMs develop along a tropical wave - Cold
upper level trough from middle latitudes - the
release of latent heat resulting from the
condensation of water vapour that has evaporated
from the warm ocean - Pressure aloft increases
due to the release of latent heat. ? High
pressure - Surface pressure drops
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
7
How hurricanes form?
Stages of development
1. Tropical disturbance lt 20 kts 2. Tropical
depression 20kts 34 kts 3. Tropical storm 34
kts 64 kts 4. Tropical cyclone (hurricane) gt
64 kts
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
8
Structure of hurricanes
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
9
Hurricane movement and origins
Hurricanes move in the general direction of the
tropospheric winds. Thus Atlantic hurricanes
typically move westward in the NE Trades and then
towards the north and northwest around the
Bermuda High. Hurricanes dissipate rapidly when
they move over cold water or over a large
landmass.
Hurricane North Atlantic Ocean, Northeast
Pacific Ocean, or South Pacific Ocean Typhoon
Northwest Pacific Ocean Cyclone Southwest
Pacific Ocean, Southeast Indian Ocean, North
Indian Ocean, or Southwest Indian Ocean
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
10
Hurricane movement and origins
Erratic paths
Paths by satellite images
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
11
Saffir-Simpson scale
- 1-5 rating based on the hurricane's present
intensity (winds). - give an estimate of the
potential property damage and flooding
Scale Pressure Winds Damage 1 980 mb 64
82kts Damage mainly to trees 2 965 979 83
95 Major damage to exposed mobile homes,
Some damage to roofs 3 945 964 96 113 Large
trees blown down. Mobile homes destroyed,
some structural damage to small
building. 4 920 944 114 135 All signs blown
down, extensive damage to roofs, major
damage to lower floors of structures near
shore. 5 lt 920 gt 135 Severe damage to windows
and doors, small building overturned and
blown away.
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
12
Naming Hurricanes
Hurricane names are chosen from an alphabetical
list of male and female names for the Atlantic
and Pacific, some of which are retired if the
storm was especially damaging.
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
13
Outcomes
Storm surge
Before
After
Folly beach, South Carolina Hurricane Hugo (Sept.
1989)
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
14
Outcomes floods
29 March 2004
31 Aug. 2005
New Orleans Hurricane Katrina (Aug. 2005)
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
15
Outcomes
For any particular location, the chance that a
hurricane will directly affect the area sometime
during the whole June to November hurricane
season
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
16
Hurricanes vs. mid-latitude cyclones
Hurricanes Energy from latent heat Warm core
cyclone, weakens with height Central clear eye,
sinking air Strongest winds at surface Circular
isobars, stronger pressure gradients, no fronts
Mid-Latitude Storms Energy from temperature
contrast Cold core low, strengthens with height
Centres of rising cloudy air Winds strongest
aloft Isobars have kinks, weaker pressure
gradients, fronts
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE