Chapter 11: Hurricanes

What factors listed below are thought to increase the number of hurricanes that form in any one hurricane season? (Select all that apply.)

*Warmer sea-surface temperatures, since they provide the needed energy to grow tropical depressions *Greater wetness in the western Sahel Region of Africa because a wetter surface provides more nuclei for hurricanes

Reduction of Hurricane Damages

*We need better planning and design. There are also numerous shortcomings common in our human-built coastal structures.

Structure of a hurricane

*They are composed of numerous thunderstorm bands that move in rotating spirals around a center. *They have convergent wind flow at low levels, rising convective clouds, and divergent winds at upper levels.

Which of the following distinguish hurricanes from storms formed at higher latitudes? (Select all that apply.)

*They can become stronger when high-altitude winds are weaker. *They are not associated with fronts. *Air in the center is warmer and descending. *Latent heat released by the condensation of water vapor is the main energy source.

How do Cape Verde-type hurricanes form? (Select all that apply.)

*They form from preexisting convective storms near the islands off northwest Africa. *They form from easterly waves, which are north-south oriented disturbances that develop within the trade winds.

Why do hurricanes that form in the eastern Pacific Ocean tend to head out to sea instead of hitting the west coast of North America? (Select all that apply.)

*Trade winds blow the hurricanes westward. (Reason: Trade winds in the Atlantic basin also blow hurricanes to the west, but there they run into land.) *Cold water at the surface along the coast robs hurricanes of their strength.

Energy flow through hurricanes (1)

*Upon reaching the eyewall, the air rises rapidly, cools, and releases latent heat of condensation that adds to buoyancy and upward velocity. *Surface winds converging on the eyewall pick up additional heat from the ocean.

From a standpoint of limiting hurricane damage, which of the following are good land-use ideas for coastal areas? (Select all that apply.)

*Use low-lying areas for parks, farms, or natural reserves instead of for buildings. *Use higher and more protected land for housing.

Cyclones in Bangladesh (1)

*Bangladesh sits largely on the low-lying delta of the Ganges and Brahmaputra Rivers built into the Indian Ocean. Cyclones commonly move up the Bay of Bengal into Bangladesh.

Why is New Orleans sinking relative to sea level? (Select all that apply.)

*Levees, built to protect the city, keep additional sediment out that would otherwise help to raise ground level. *Global sea level is rising. *It is built on delta sediments, and it is the nature of those deposits to compact and subside.

Building codes call for protecting the roof as the number one priority for safe buildings during hurricanes. Which of the ways listed below are thought to help with that goal?

*Remove or strengthen eaves (projections) that stick out from the roof. *Strap roofs to walls.

Which of the following are true about the Accumulated Cyclone Energy (ACE) index? (Select all that apply.)

*The ACE is a measure of the total energy output of a hurricane. *The total energy released by each hurricane in a season is complied. *Hurricane Ivan in 2004 released more energy than is generated in some entire hurricane seasons.

Natural Disaster Tip

As she reached the third level, flood water shut off power to the elevator. The slowly rising water drowned the unfortunate woman trapped in her elevator jail. Remember: Do not use elevators during natural disasters.

Hurricane Katrina

On 24 August 2005, a tropical air mass over the Bahamas grew powerful enough to be given a name—Katrina. Two hours before reaching Florida on 25 August, Katrina had grown to be a hurricane. Katrina lost strength crossing Florida, but after reaching the warm waters of the Gulf of Mexico, the storm grew rapidly, with wind speeds reaching 280 km/hr (175 mph) and its size nearly doubling.

Conditions that favor Cape Verde- and Caribbean/Gulf of Mexico-type hurricanes include ________ sea-surface temperatures and __________ atmospheric pressure conditions in the Caribbean.

Warm, High Low

Which of the following best describes the forecasting of hurricanes by the National Hurricane Center?

They have greatly improved hurricane forecasting, and that has saved thousand of lives by permitting timely evacuations.

Tropical Disturbance

A low-pressure system in the tropics characterized by thunderstorms and weak surface wind circulation.

Atlantic Multidecadal Variability (AMV)

An Atlantic Multidecadal Variability (AMV) has been recognized based mainly on sea-surface temperatures in the North Atlantic Ocean. A reasonably distinct pattern appears to exist, showing alternating times of colder versus warmer water. The AMV involves variability in oceanic, atmospheric, and other natural processes as well as human-induced changes.

Hurricane Andrew, August 1992

Andrew was born in Africa. On 13 August, it had developed into thunderstorms over West Africa. It then moved out over the Atlantic Ocean as rainy, low-pressure wind waves that converged at low angles to form a rotating air mass. By 17 August, the central circulation had intensified into a tropical storm, but high-level winds disrupted the upward growth of the rotating core of clouds.

Tropical Cyclone

Any weather system formed over tropical waters that rotates counterclockwise in the Northern Hemisphere.

Hurricane Hugo- September 1989

Hugo came to town as the 10th strongest hurricane in the 20th-century United States. Hugo brought a 5.2 m (17 ft) high surge to Fort Sumter and 220 km/hr (135 mph) winds; it was a category 4 hurricane. The move onto land cut Hugo off from its warm-water energy supply. With decreasing energy, the storm adopted a curving path; a prominent northward hook led past the west side of Charlotte, North Carolina, at tropical-storm intensity at 6 a.m. Friday.

Hurricane Mitch, October 22, 1998- November 9, 1998

Hurricane Mitch began in the Caribbean Sea on 22 October 1998. Mitch stalled offshore from 27 to 29 October, dumping enormous volumes of rain on Honduras and Nicaragua. On 3 November, Mitch entered the Gulf of Mexico, picked up strength from the warm water, and headed northeast across the Atlantic, traveling north of England on 9 November.

Cyclones in Bangladesh (2)

Much of Bangladesh is low-lying river-delta land where cyclone storm surges kill many thousands of people. This photo from space shows multiple rivers winding through heavily populated mud flats.

East Side of wave axis

On the east side of the wave axis, the low-level winds converge and rise, forming clouds with rain.

Making a home more resistant to hurricane damage includes which of the following?

Protecting and sealing doors and windows, so winds cannot get inside.

Hurricanes in the Atlantic basin seem to have decades-long patterns of activity. Which long-term pattern below seems to be linked to this?

The Atlantic Multidecadal Oscillation (Reason: The Atlantic Multidecadal Oscillation is a pattern of warm and cold sea-surface temperatures.)

Hurricanes do not form at or within 5°N or S of the equator because ______.

The Coriolis effect is too weak

What path does the majority of hurricanes that form in the eastern equatorial Pacific Ocean take?

They head westward out into the Pacific Ocean.

If people cannot run far and high enough to escape an oncoming hurricane, what should they do?

They must seek out local shelters built strong enough to withstand the hurricane attack and high enough to avoid flooding by the storm surge. As a general rule: *Run from the water. *Hide from the wind.

Post-tropical cyclone

often between 30° and 40° latitude, if there is sufficient collision with upper-level troughs in the westerly wind belt. The collision forces a hurricane to tilt back into a colder air mass, disrupting convection up the eyewall and thus cutting off its primary source of energy—the latent heat of condensation supplied by thunderstorms near the hurricane center. When a hurricane ceases to have warm, moist air flowing up its warm core, it can turn into a cold core and the hurricane body can merge with the colliding weather front. The combined weather system may increase in size as the hurricane transforms.

Hurricane Camille

one of three category 5 hurricanes to hit the United States since 1900. Camille brought winds gusting over 320 km/hr (200 mph) that hit Mississippi in 1969 with a sea surge of 7.3 m (24 ft); this caused many of the 256 fatalities. Fatal sites included the three-story brick buildings of the seaside Richelieu apartment complex where, instead of evacuating, 32 party-hearty people held a "hurricane party" to celebrate the event—it was the last party for 30 of them

Isotherms

the lines of equal temperature (T). The T = 10°C (50°F) isotherm rises up markedly to define the warm core of the hurricane. The warm core is due to the release of huge quantities of latent heat from rising winds and to adiabatic warming of the sinking air in the eye. At the sea surface, temperatures in the eye may be only 0-2°C (0-3°F) warmer than surrounding air, but at altitudes of 10-12 km (6-7 mi), the temperatures within the warm core may be 11°C (20°F) warmer than the surrounding environment.

Hurricane

A large, tropical cyclonic storm with wind speeds exceeding 119 km/hr (74 mph); called a typhoon in the western Pacific Ocean and a cyclone in the Indian Ocean

Tropical Depression

As surface winds strengthen and flow more efficiently around and into the center of the growing storm, it becomes a tropical depression and receives an identifying number. The Coriolis effect is the mechanism that spins the storm in a counterclockwise (cyclonic) rotation around a central core in the Northern Hemisphere. The converging surface winds meet at the central core, which acts like a chimney, sending warm, moist air flowing rapidly upward toward the stratosphere (figure 11.4). The rising moist air cools and reaches its dew point temperature where water vapor condenses, thus releasing prodigious quantities of latent heat. The released heat warms the surrounding air, causing stronger updrafts, which in turn increase the rate of upward flow of warm, moist air from below.

Temperature in Hurricane development

As the sea-surface temperature increases, the amount of water vapor that air can hold increases exponentially. When 27°C is exceeded, the amount of latent heat lifted from the tropical ocean easily becomes large enough to fuel a hurricane. Hurricane Katrina picked up tremendous amounts of heat from the warm Gulf of Mexico water

Eye

Forms in the center of a hurricane when wind speeds exceed 119 km/hr (74 mph). Descending air in the eye warms, causing clear air.

As stronger winds cause waves to grow larger, the amount of energy lost to ______ increases as the wind moves over the ocean.

Friction

Which of the following describes the hurricane threat in Hawaii?

Hawaii sits at the northern edge of warm water capable of producing hurricanes and is sometimes stuck by them

Surges

Hurricanes can push massive volumes of seawater onshore as surges that temporarily raise sea level more than 6 m (20 ft). Their heavy rains can cause dangerous floods, killing people well away from the coastline, and tornadoes may spin out from their clouds.

Tropical Storm

If the converging winds continue to spiral up the core wall at ever-increasing speeds, then the cyclonic system grows in strength. When sustained surface-wind speeds exceed 63 km/hr (39 mph), it has become a tropical storm (surface winds from 39 to 74 mph).

Accumulated Cyclone Energy (ACE)

Measure of energy expended by a tropical cyclone. Values are totaled to measure energy released during an entire season.

What has been the proven impact of stronger building codes in reducing hurricane-related damage to mobile homes in Florida?

Mobile homes built to higher standards suffered less damage than those built to lower standards.

What will happen to the many thousands of expensive new buildings lining the shoreline?

They will be hit and damaged by hurricanes bringing wind, storm surges, waves, and heavy rain.

Location of the ITCZ

The location of the ITCZ moves with the seasons. The average position of the ITCZ is about 5°N latitude. In January, it mostly lies south of the equator, but by July, all the ITCZ is north of the equator.

Which of the following is the century-long trend in the United States related to hurricane destruction?

The number of deaths have been decreasing, and the economic damages have been increasing.

Which of the following accurately compares the yearly number of hurricanes in the eastern Pacific to those in the North Atlantic/Caribbean Sea/Gulf of Mexico basin?

There are about 25% more hurricanes in the eastern Pacific.

Which of the following statements is true about hurricanes, cyclones, and typhoons?

They are all the same basic storm with different names from different regions.

Hurricanes are Tropical Cyclones

They are heat engines that convert the heat energy of the tropical ocean into winds and waves. These powerful storms can generate winds more than 240 km/hr (150 mph) (

Where do the hurricanes that effect Hawaii come from?

They come from the south and follow a right-hooking path to get there.

Roofs

(1) Builders should eliminate or strengthen eaves that project out from roofs, thus making it harder for winds to lift off roofs. (2) Strap roofs to walls. Inside the attic where the roof meets the walls, add numerous hurricane straps to help hold the roof to the walls. Straps are heavy belts of material similar to those used on suitcases or backpacks. Each strap is wrapped around a roof rafter and a heavy stud in the wall, then fastened by numerous nails. (3) Ban the common practice of using rapid-fire staples to secure thin asphalt roofing sheets onto plywood roofs. Hurricane winds easily strip off these lightweight, flexible materials and thus gain entry to the house.

Requirements for Hurricanes

(1) Seawater should be at least 27°C (80°F) in the upper 60 m (200 ft) of the ocean; (2) air must be warm, humid, and unstable enough to sustain convection; (3) the storm must be far enough (∼500 km = 300 mi) from the equator for a Coriolis effect to be strong enough to spin the system; and (4) upper-level winds should be weak and preferably blowing in the same direction the developing storm is moving.

Hurricane Paths are hard to predict

(1) They must adjust to other high- and low-pressure atmospheric systems they encounter (2) Trade winds blow tropical cyclones toward the west. (3) The Coriolis effect adds a curve to the right that progressively increases in strength with distance from the equator. (4) An extensive high-pressure zone called the Bermuda High commonly sits above the North Atlantic Ocean. Hurricane paths vary depending on the size and position of the Bermuda High and other steering currents

How can you reduce the hazard posed to houses from wind-borne debris in a hurricane?

*Eliminate potential debris by picking up and storing outside items, and encouraging others to do the same. *Exterior glass must be shatterproof or protected by shutters or plywood.

Which of the following are known to strongly influence the path of hurricanes in the Atlantic Ocean? (Select all that apply.)

*Existing high- and low-pressure systems they encounter *The changing strength of the Coriolis effect with latitude *The trade winds

Which of the following are true about the hurricane season in the Atlantic and U.S. Gulf coast? (Select all that apply.)

*Hurricanes and/or their weaker forms (e.g., tropical storms) form every year. *Hurricanes will form when sea-surface temperatures are at their warmest.

Which of the following are accurate about the naming of hurricanes in the North Atlantic basin? (Select all that apply.)

*Hurricanes are currently named using both typically male and typically female names. *When a hurricane is particularly deadly or destructive, the name is never used again. *If more than 21 named storms occur in a year, the rest are named after letters in the Greek alphabet.

Which of the following are true about inland flooding caused by hurricanes? (Select all that apply.)

*Inland flooding from hurricanes is a hazard even in states without a coastline. *In the United States, inland flooding causes more deaths than storm surges.

Why do hurricanes need warm sea-surface temperatures to form? (Select all that apply.)

*It increases the amount of water vapor that can be stored in the atmosphere by warming the air from below. *Warmer water evaporates at a faster rate, and this transfers latent heat into the storm more quickly.

Which of the following would be typical for a hurricane in the North Atlantic-Caribbean-Gulf of Mexico region? (Select all apply.)

*It is large and lasts from 1 to 30 days. *It forms in the late summer.

Which of the following factors contribute to making a hurricane's storm surge higher? (Select all that apply.)

*Larger waves brought by the storm *High tides

Which of the following accurately describe the flow of energy in a hurricane? (Select all that apply.)

*Surface winds converging on the eyewall pick up additional heat from the ocean. *Upon reaching the eyewall, the air rises rapidly, cools, and releases latent heat of condensation that adds to buoyancy and upward velocity. *Air flowing outward from the top of a hurricane loses heat via long-wavelength radiation.

Why are the tropical cyclones that hit Bangladesh particularly deadly? (Select all that apply.)

*The country is low-lying, making flooding more likely. *The country is densely populated.

What are the natural conditions that help to increase the threat from cyclones in Bangladesh? (Select all that apply.)

*The topography and orientation of the land and water funnel storms toward Bangladesh. *The country mostly sits atop of low-lying delta sediments, and they are sinking as they compact.

Why is storm surge highest near to and to the right of the eye of a hurricane? (Select all that apply.)

*The winds there are blowing onshore as opposed to the offshore winds on the left side of the eye. *Low atmospheric pressure in the eye allows water to pile up there.

Land-Use Planning

. A recent study for the Federal Emergency Management Agency (FEMA) estimates that during the next 60 years, 25% of houses within 150 m (500 ft) of the shoreline will fall into the water unless mitigating actions are taken, such as adding sand to beaches, adding riprap, or building hard walls.

In low-lying areas of the Gulf and Atlantic coasts, how much sea level rise is needed to move the ocean front 1,000 ft inland?

1 Foot

Global sea level rose ______ in the 20th century, and it is likely to rise ______ more in the current century (the 21st).

1 ft; 2 ft

Hurricane Energy Release

A hurricane acts as a heat engine, transferring heat from the warm, moist air above tropical seas into the core of the hurricane. As air rises into the hurricane, latent heat is released in staggering quantities. The average hurricane generates energy at a rate 200 times greater than our worldwide capacity to generate electricity. The kinetic energy of winds in a typical hurricane is about half our global electrical capacity. Summing up, the energy released in a hurricane by forming clouds and rain is 400 times greater than the energy of its winds.

Rain bands of a hurricane

Bands of heavy rain showers that spiral inward toward the storm's center. Surrounds the eye wall.

Cyclones in Bangladesh (4)

Bangladesh has a 575 km (360 mi) long coastline shaped like a funnel that catches the cyclones roaring up and over the warm waters of the Bay of Bengal . About five cyclones per year enter the Bay of Bengal both before (April-May) and after (October-November) the southwest monsoon season.

Hurricane Katrina- New Orleans

By 26 August, computer models identified New Orleans as a possible target with a 17% chance of a direct hit. Many residents were nervous; they knew that most of the city of New Orleans lay below sea level and that Katrina would bring huge volumes of water. As 27 August dawned, residents saw that Katrina had moved ever closer. More warnings were issued. People began shuttering their homes, grabbing prized possessions, and fleeing. On the morning of 28 August, the situation looked even worse, causing a mandatory evacuation to be ordered for 1.2 million residents.

The inward drop in air pressure in a hurricane allows inward flowing air to ___________ below the sea-surface temperature, which in turn allows more heat to flow in from the sea.

Cool

The air inside a hurricane is ascending, whereas just outside the storm the air is _______ ,creating clear skies.

Descending or Subsiding

Hurricanes in the North Atlantic Ocean are large, mobile, and long-lasting

Each year, from 4 to 28 tropical storms and hurricanes occur in the North Atlantic-Caribbean Sea-Gulf of Mexico region. The coastline of the United States is frequently crossed by landfalling tropical cyclones

Easterly Wave

Easterly waves are disturbances or mega-ripples that develop within the trade winds; they are elongate, north-south oriented, and extend 2,000 to 3,000 km (1,200 to 1,900 mi).

Small twisting vortices analogous to eddies in a river or to tornadoes.

Embedded in the body of the hurricane were small twisting vortices analogous to eddies in a river or to tornadoes. The twisting eddies were about 150 m (500 ft) in diameter, and many were sucked up into the eyewall. When they drifted into the intense updrafts of the eyewall, they were stretched vertically, decreasing their diameters and increasing their speeds to about 80 mph. Consider the effects on the ground.

True or false: Thanks to better construction methods and advanced warnings, the economic and loss of human life caused by hurricanes has been dropping over the last 100 years in the United States.

False *Reason: Construction methods have improved, but more buildings and more expensive homes are being built along the coast. While deaths are down, the economic costs are up.

The best building codes related to limiting hurricane damage proved to be those that required a design that ______.

Passed the wind energy from the roof, to the walls, and to the ground

Tornadoes form in some hurricanes

Most commonly in the right-front quadrant of the hurricane in outer rain bands some 80-500 km (50-300 mi) from the hurricane center. Tornadoes are most likely to form in hurricanes that are: (1) large, intense, and strongly curving; (2) moving forward at 12-30 km/hr (8-18 mph); (3) interacting with old, weakened fronts; and (4) over land. Tornadoes are more likely when hurricanes interact with land. The surface winds slow down due to friction with the land, while the winds aloft keep up their momentum, creating the necessary vertical wind shear for rotation.

West Side of wave axis

On the west side of the wave axis, the upper-level winds diverge and sink, resulting in clear skies.

Hurricane Andrew's Damages

Once a window breaks, hurricane winds enter a house, tear up the inside, and lift off its roof. A study of Andrew's damages concluded that up to 40% of the losses could have been avoided if buildings had been constructed to meet the wind-resistance standards of the South Florida Building Code. Poor construction and lax enforcement of building codes caused much unnecessary suffering.

Wind-Borne Debris

Once an opening exists in a building, the winds can come inside and intensify their destruction. To prevent penetration, all exterior glass windows and sliding-glass doors should be made of shatterproof glass or be protected by shutters. If the building does not have built-in shutters, plywood should be precut to fit over all windows and sliding-glass doors.

Evacuation Dilemma

Population grows far faster than new roads and bridges are built. Moving large numbers of people out of harm's way is a time-consuming operation complicated by the limits of weather forecasting, by human psychology, and by transportation systems that do not allow free-flowing movements even with fewer vehicles in perfect weather.

The Intertropical Convergence Zone (ITCZ)

The ITCZ is a major site of convergence of warm, moist, low-level winds that rise high, forming a nearly continuous ring of thunderstorms surrounding the Earth. Thunderstorms are a daily event along the ITCZ, and occasionally a cluster of thunderstorms breaks away and organizes into a more unified system. Add some rotation to these convective columns and a tropical cyclone is born.

Why are there often clear skies around a hurricane?

The air diverging out of the top of the hurricane warms adiabatically as it sinks and evaporates clouds on its way down.

Hurricane eyewalls contain the highest wind speeds because ______.

The biggest drop in air pressure occurs there (Reason: Recall that winds move from high to low pressure and greater differences in air pressure result in higher wind speeds.)

Eyewall

The eyewall is an eye-encircling ring of tall thunderstorms that typically have the highest wind speeds and heaviest rainfall in a hurricane. Air in the eyewall spirals upward and outward.

Cyclones in Bangladesh (3)

The nation has densely populated a comparatively small area. Because Bangladesh has a rapidly growing population and scarce land and food, it is little wonder that many millions of people are driven to the rich delta soils that yield three rice crops per year. The delta country is low-lying, most of it a foot or less above sea level; more than 35% of Bangladesh is at less than 6 m (20 ft) elevation.

Decisions made about land use before development takes place can prevent a lot of damage

Think of the destruction that could be avoided if cities and counties designated low-lying coastal land for use as parks, farm fields, golf courses, nature preserves, or other uses where flooding will cause fewer problems. At the same time, the higher and more protected land could be zoned for house and business construction.

Tropical Storm Allison

Tropical Storm Allison poured rain onto Houston, Texas, on 7 June 2001, and then left the city only to return unexpectedly on 9-10 June. On its return, Allison dumped 36 cm (14 in) of rain onto the already saturated ground. Flooding drowned 2,500 animals involved in medical research at the Texas Medical Center and claimed the lives of 24 people in the region.

True or false: There are more hurricanes in the eastern Pacific Ocean than in the North Atlantic/Caribbean Sea/Gulf of Mexico every year.

True

Manufactured Homes

When Florida was hit by four hurricanes in 2004, countless old mobile homes were destroyed, but the new ones built to meet the tougher standards fared well. The Florida Manufactured Housing Association admitted that it had been wrong to oppose the new rules.

The Bermuda High

When the Bermuda High is small and to the east, hurricanes may curve northward around it and have little or no effects on coastlines When the Bermuda High is strong and extensive, it may guide hurricanes along the east coast of the United States, causing widespread death and destruction as resulted from the New England hurricane of 1938, Diane in 1955, Donna in 1960, and Agnes in 1972.