Download Geographic Regions at Risk for Cyclones, cont.

Geography 1700
Chapter 9
Part 2 of 4
 “Super-Storm Sandy” in October, 2012 caused more than
$55 Billion in financial losses and cost more than 300 lives.
 Most of these losses were preventable. People living along
the sea coast are “gamblers” - - hoping that a big storm
won’t really affect them.
 As of October, 2013, some people in New Jersey still do
not have electricity and/or drinking water.
 People in New Jersey can say the same thing about us:
people in Utah think that a big earthquake won’t really be
that bad.
Extra-tropical Cyclone
Development

Low pressure develops along fronts.
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Cold front on southwest, warm front on east.
Cold air circulates counter-clockwise.
Warm air rises on the southeast side.
Dry air aloft feeds the cyclone from behind the cold front.

Occluded front develops, trapping warm air aloft.

Pressure gradient weakens and storm dissipates.
Air will flow when there is a ‘gradient’ or “slope” between high
and low pressure. Air pressure results from differences in
temperature. High pressure flows to low pressure. WIND.
Hurricanes in East and Gulf
Coasts

Usually takes one of three
paths

Season starts June 1 and
ends Nov 30
Figure 9.21
Geographic Regions at Risk
for Cyclones
But what about
“tornado alley”?
Let’s broaden
our definition
of “cyclone”
Geographic Regions at Risk for Cyclones, cont.
What makes the USA so
unusual in severe storms?
Because, we should have desert in Alabama - - but we
don’t. Instead, we have “fight club” -- ”tornado alley”.
Track of Extra-Tropical Storms
Trade winds from east to west collect ocean transfer ocean heat to air
vapor where it can collide with drier air further north.
This red arrow is
probably wrong.
Hurricanes do not
reach Los Angeles.
Hurricanes west of Mexico
tend to blow away from land
because of the same trade
winds that blow hurricanes
toward land in the Gulf and
Atlantic.
Geographic Regions at Risk
for Cyclones
Our definition of
‘cyclones’ should
include “tornado alley”.
All together, the
United States
collects more than
90% of the world’s
tornadoes.
The coast is
“hurricane”
country, but
cyclones
include
tornadoes that
occur across
much of the
USA.
Hurricane
regions are
also tornado
regions.
Geographic Regions at Risk
from Cyclones, Summary

Tropical cyclones
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East and Gulf Coasts
Hawaii and Atlantic Canada
Baja California and West Coast Mexico
Extra-tropical cyclones
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Winter windstorms in Pacific Coast
Winter snow Sierra Nevada, Rocky Mountains, and east
Spring and summer thunderstorms and tornadoes in U.S. and
Canada
A classic “extra-tropical”
cyclone. In our hemisphere they
are called hurricanes.
Notice the tall clouds, welldeveloped “eye” and the
counter-clockwise winds.
Low air pressure inside these
storms (rising air) allows ocean
levels to rise also, allowing
‘taller’ sea level during the
storm.
High winds and heavy rain then
add much more to ‘storm surge.’
Flooding.
600+ miles wide
Looking down on a cyclonic storm, notice that the right
side probably exhibits higher wind speeds because the
forward speed of the storm adds to the wind speed inside
the storm.
If wind speed inside the
storm reaches 100 mph
and if the entire storm is
moving forward at 20 mph,
then the combined speed
of wind on the forwardmoving side should be
120 mph.
Likewise, the “back side”
of the storm subtracts
forward speed to yield
just 80 mph winds.
Higher wind means higher
storm surge flooding.
Is it true that
tropical storms
can become
stronger when
they take their
energy (heat) into
encounters with
cooler/drier air?
For the same reason a
‘dust devil’
hit Mr. Allred’s
car twice.
Still, it is important
that dry dust devils
rise only until they
lose their heat source,
such as a black
asphalt parking lot.
But wet tornadoes
contain their own
source of heat –
latent heat in
invisible water vapor.
They rise until they
run out of water &
heat.
Can you see why cyclonic
storms can “hit” twice?
Westerlies – cooler/drier
Trade winds flow
east to west.
After collision with
westerlies, storm
fronts tend to flow
SW to NE.
Calculate net wind
speed right front vs
left rear.
Easterly Trade Winds – warmer/wetter
Facing the on-coming storm, calculate the left
vs right side wind speed differential to show
why the storm is often worse on one side or
the other.
Wind speed 100 mph
Storm track 20 mph.
Can you see why
cyclonic storms
can “hit” twice?
What about a
‘dust devil’
hitting Mr. Allred’s car?
Cyclone Effects: High Winds

Described by Saffir-Simpson
Scale

Decrease exponentially with
landfall

Strongest recorded winds in
U.S. from extra-tropical
cyclone

Responsible for strong winds in
blizzards and tornadoes
Figure 9.28
Cyclone Effects: Storm Surge
1. Low atmospheric pressure allows sea water to rise as much as three
feet, like drawing soda up a straw.
2. High winds can push storm water far upstream and inland, adding
perhaps 6-10 feet of flooding above normal sea level.
3. High winds can cause severe damage even without water involved.
4. High winds cause higher and faster wave crests that push inland.
5. Heavy rain can cause downstream flooding even as sea water is
pushing upstream. People live in between and sometimes drown.
6. Flooding is even worse if the storm coincides with high tide. Spring
tide would be worse yet = Super Storm Sandy had it all – 20 feet of
surge in some places.
Combined total flooding in a hurricane can even exceed 30 feet.
Links to Other Natural
Disasters

Coastal erosion
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Flooding
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Mass wasting
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Other types of severe weather

Tornadoes, severe thunderstorms, snowstorms, and blizzards
Natural Service Functions of
Cyclones

Source of precipitation -- Many places depend on severe
storms to help meet annual water budget.
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Redistribute warm air from tropics
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Maintain ecosystems
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Winds carry plants, animals, and microorganisms.
Waves stir up deeper, nutrient-rich waters.
Winds topple weak and diseased trees in forests.
Waves break apart some corals.
Human Interaction with
Cyclones

Urbanization of vulnerable coastlines
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Destruction of sand dunes
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Construction of seawalls and bulkheads
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Poor building materials and practices
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Global warming
Forecasting and Warnings
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Forecast includes:
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If it will make landfall
Where and when
Wind strength
Rainfall amount
Storm surge
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Monitored by U.S. Hurricane Center, Canadian
Hurricane Center.
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Hurricane watch means likely hurricane in 36 hrs.
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Hurricane warning given when hurricane is likely
within 24 hrs or less.
Forecasting Tools
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Weather satellites
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Aircraft
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Detect early warning signs
Cannot show wind speed
U.S. Air Force, NOAA airplanes fly into the storm to collect
data
Doppler radar
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Give information on rainfall, wind speed, and direction of the
storm
Forecasting Tools, cont.
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Weather buoys
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Automated weather stations that give information at their
locations
Computer models
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Predict and track hurricane progress
Have vastly improved hurricane information
Still lacking in predicting storm intensity
Storm Surge Predictions

Predict the time and elevation of surge.
 Forecasters use wind speed, fetch, and average water depth.

Need detailed information on topography.
 Different elevations on land affect the storm surge.

Computer models use central pressure, size, forward speed, track, wind
speed, and seafloor topography.
Let’s keep in mind that prediction is still an issue –
even though we can see a hurricane coming, we don’t
know how each part of the storm will match-up with a
coastline and urban areas.
The result is sometimes widely varying differences in
storm surge and people who get caught by surprise.
Hurricane Prediction and the Future

Deaths have decreased dramatically because of better
forecasting, improved education, and greater public
awareness.
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However, coastal populations are increasing, causing an
increasing risk.
Perception of and
Adjustment to Cyclones
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Perception of hazard depends on personal experience.
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More experienced people may take hazard more precautions.
More experienced people may also take less precautions.
Community adjustments to cyclone hazard:
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Warning systems (Hurricane Katrina may have been the most advertised
disaster in human history. The whole world watched it develop).
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Evacuation plans and shelters
Insurance
Building design
Tornado warnings in the United States used to be
only 2-3 minutes before arrival.
Tornado warnings now provide as much as 11 minutes
of warning.
How do tornado warnings compared to hurricane
warnings?
Hurricanes are known well in advance – tornadoes
are often too small and quick-moving for the forecast.
Remember:
- a “watch” means that an event might happen
- a “warning” means that something IS happening – take cover.
Perception of and Adjustment to
Cyclones, cont.
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Personal adjustments to cyclone hazard
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Be aware of hurricane season
Prepare homes and property for hazard
Obtain flood insurance
Install heavy shutters that can be latched
Learn evacuation route
Make a family emergency plan
Collect emergency supplies