ATS 351, Spring 2009
Week 13, Lab #11 - Answer Key
Hurricanes - 60 points
Question #1: Hurricane Structure (10 points)
a) (4 points) On the plot below, label in the regions provided: the eye, eye wall, and
spiral rain band. Also indicate the direction of rotation of the hurricane (at low
levels).
Rotation is counterclockwise
Eye
Eye wall
Spiral Rain
Bands
b) (6 points) Describe each of the regions and why they exist:
a. Eye: The eye is the region at the very center of the hurricane that generally
has broken clouds and lower wind speeds. High pressure aloft is created
from the warming of the air due to latent heat release, which creates
downward motion at the center of the storm.
b. Eye wall: A ring of intense thunderstorms adjacent to the eye where the
highest winds and heaviest rains are found. Winds move in towards the
center of the low at the surface and the eye wall is formed by intense
rising motion and convection around the eye.
c. Spiral rain band: The rising and sinking motion areas within a hurricane
create areas of convection next to areas of sinking motion. Clouds align
themselves into spiraling bands that swirl towards the center of the low.
Question #2: Formation (10 points)
a) (2 points) Why is a hurricane more likely to form in October than in May?
The oceans heat up during the summer and therefore the highest
temperatures are found in the fall and not prior to the summer heating. Since
hurricanes gain energy from latent and sensible heat fluxes from the warm ocean
surface, the warmer the temperatures, the greater the fluxes and the more likely a
hurricane will form. Therefore, formation is more favorable for hurricanes in
October as opposed to May.
b) (4 points) Why do hurricanes form over the ocean and dissipate over the land?
As it was said above, hurricanes gain energy from latent and sensible heat
fluxes from the warm ocean surface. When hurricanes move over land, this
source of energy is gone and hurricanes will dissipate. Also, friction increases
when hurricanes move over land, which decreases wind speeds. This also helps
to weaken the storm.
c) (4 points) There are two other common names for a hurricane that are used
regularly in other parts of the world. What are these names, and where are they
used?
Cyclone: India/Australia
Typhoon: Western North Pacific
Question #3: Stages of Development (12 points)
a) (8 points) Please list the 4 stages of hurricane development and describe the
characteristics of each stage.
Tropical disturbance: a group of thunderstorms with slight circulation
Tropical depression: when winds exceed 20 knots and the formation of the closed
low begins; on satellite, it appears as a cluster of thunderstorms; it is given a
number at this point
Tropical storm: winds exceed 35 knots and the central pressure drops; on satellite,
there is a more organized, circular shape and the storm gets a name
Hurricane: winds exceed 64 knots and surface pressure continues to drop; on
satellite imagery, clear cyclonic rotation around the center.
b) (4 points) What feature of a hurricane is responsible for the greatest percentage of
human casualties and damage when the storm makes landfall? Where can this
feature be found within the storm, relative to the storm’s direction of movement?
Storm surge; it is strongest where the storm motion and winds are in the same
direction which is on the right side of the hurricane.
Question #4: Major Hurricanes (28 points – 4 each)
Use the Internet to find the maximum Saffir-Simpson scale category achieved, location
and date of landfall in the United States, the estimated damage in US dollars, and at least
one or more interesting facts that are associated with the following major hurricanes.
a) Galveston hurricane, 1900
Saffir-Simpson scale: category 4
Date: September 8, 1900
Where: Galveston, Texas
Estimated damage: $20 million in 1900; $516 million in 2009
b) Florida Keys Labor Day hurricane, 1935
Saffir-Simpson scale: category 5
Date: September 2, 1935
Where: upper Florida Keys
Estimated damage: $6 million in 1935; $94 million in 2009
c) Hurricane Donna, 1960
Saffir-Simpson scale: category 5
Date: September 9, 1960 (accept 10th too)
Where: middle Florida Keys
Estimated damage: $900 million in 1960; $6.5 billion in 2009
d) Hurricane Hugo, 1989
Saffir-Simpson scale: category 5
Date: September 21, 1989
Where: South Carolina
Estimated damage: $10 billion in 1989; $17.4 billion in 2009
e) Hurricane Mitch, 1998
Saffir-Simpson scale: category 5
Date: November 5, 1998
Where: Gulf Coast of Southern Florida
Estimated damage: $6.2 billion in 2009
f) Hurricane Ivan, 2004
Saffir-Simpson scale: category 5
Date: September 16, 2004
Where: Gulf Shores, Alabama
Estimated damage: $16.4 billion in 2004; $18.7 billion in 2009
g) Hurricane Katrina, 2005
Saffir-Simpson scale: category 5
Date: August 23, 2005 & August 29, 2005
Where: Southern Florida then New Orleans, Louisiana
Estimated damage: $81.2 billion in 2005; $89.6 billion in 2009