Geography 1700Chapter 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.

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

Figure 9.21

Usually takes one of three paths

Season starts June 1 and ends Nov 30

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”.

Westerlies

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.

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.

This red arrow is probably wrong. Hurricanes do not reach Los Angeles.

Geographic Regions at Risk for Cyclones

Our definition of ‘cyclones’ should include “tornado alley”.

The coast is “hurricane” country, but cyclones include tornadoes that occur across much of the USA.

Hurricane regions are also tornado regions.

All together, the United States collects more than 90% of the world’s tornadoes.

Geographic Regions at Risk from Cyclones, Summary Tropical cyclones

East and Gulf Coasts Hawaii and Atlantic Canada Baja California and West Coast Mexico

Extra-tropical cyclones 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, well-developed “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.

Storm forward

track = 20 mph

Higher wind speed

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 forward-moving 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.

Lower wind speed

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’scar 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?

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.

Westerlies – cooler/drier

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 stormscan “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 Surge1. 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

Flooding

Mass wasting

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.

Redistribute warm air from tropics

Maintain ecosystems 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

Destruction of sand dunes

Construction of seawalls and bulkheads

Poor building materials and practices

Global warming

Forecasting and Warnings Forecast includes:

If it will make landfall Where and when Wind strength Rainfall amount Storm surge

Monitored by U.S. Hurricane Center, Canadian Hurricane Center.

Hurricane watch means likely hurricane in 36 hrs.

Hurricane warning given when hurricane is likely within 24 hrs or less.

Forecasting Tools Weather satellites

Detect early warning signs Cannot show wind speed

Aircraft U.S. Air Force, NOAA airplanes fly into the storm to

collect data

Doppler radar Give information on rainfall, wind speed, and

direction of the storm

Forecasting Tools, cont.

Weather buoys Automated weather stations that give information at

their locations

Computer models 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.

Allred’s Note

Hurricane Prediction and the Future

Deaths have decreased dramatically because of better forecasting, improved education, and greater public awareness.

However, coastal populations are increasing, causing an increasing risk.

Perception of and Adjustment to Cyclones Perception of hazard depends on personal

experience. More experienced people may take hazard more

precautions. More experienced people may also take less

precautions.

Community adjustments to cyclone hazard: Warning systems (Hurricane Katrina may have been the most

advertised disaster in human history. The whole world watched it develop).

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. Personal adjustments to cyclone hazard

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