ch 11 hurricanes · • large tropical cyclones • heat engines converting heat of tropical ocean...

11-1

Natural DisastersTenth Edition

Chapter 11Hurricanes

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11-2Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 11-2

Hurricanes

• Large tropical cyclones

• Heat engines converting heat of tropical ocean into winds, waves

• Generate winds over 240 km/hr

• Push massive amounts of water onshore as surges, up to 6 m over sea level

• Heavy rains cause dangerous floods well away from coastlines

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 11-3

Figure 11.3 Hurricanes


How a Hurricane Forms (1 of 3)

• Means of transporting excess tropical heat to mid-latitudes

• Requirements for development of hurricane:

– Seawater at least 27oC (80oF) in upper 60 m

– Air must be warm, humid and unstable

– Weak upper-level winds, preferably blowing in same direction as developing storm is moving



• Begins with tropical disturbance:– low-pressure zone drawing in cluster of thunderstorms

with weak surface winds

– Converging surface winds flow up central core (like chimney) sending warm, moist air into stratosphere

– Rising moist air cools to dew point temperature, condenses and releases latent heat

– Released heat warms surrounding air stronger updrafts increased rate of upward flow of warm, moist, surface air

– When winds exceed 63 km/hr: tropical storm

– When winds exceed 119 km/hr: hurricane



• Storm becomes tropical depression(receives identifying number):

– Surface winds strengthen and flow around and into core

– Rotates counterclockwise (in Northern Hemisphere)


Figure 11.4 Hurricane Katrina grows in strength moving over unusually warm

seawater


Figure 11.5 How a Hurricane Forms


How a Hurricane Works (1 of 3)

The Eye

• As more wind blows into center of tropical storm, difficult for all wind to reach center spiraling

upward cylindrical wind mass in center of storm

• When surface-wind speeds reach about 119 km/hr, none of wind reaches center calm clear eye

• Inside eye:

– Cool, high-altitude air sinks and absorbs moisture

• Eye wall:

– Cylinder-shaped area of spiraling upward winds around eye

– Strongest winds



The Eye

• Eddies of storm sucked up into eye wall and stretched vertically caused winds on one side

of 130 mph + 80 mph = 210 mph, and winds on other side of 130 mph – 80 mph = 50 mph

• Same phenomenon occurs on different sides of storm: one side experiences wind speed + travel speed of hurricane, other side experiences wind speed – travel speed of hurricane



Hurricane Energy Release

• Transfers heat from tropical seas to core of hurricane

• Huge amounts of latent heat released as air rises

• Generates energy at 200 times greater rate than worldwide electricity-generating capacity


Figure 11.10 Energy Flow within a Hurricane


Figure 11.27 How a Hurricane Works


Hurricane Origins (1 of 3)

• Differences from high-latitude storms:– Main energy source is latent heat released by water

vapor condensation

– Weakens rapidly when moves onto land

– Not associated with fronts

– Weaker high-altitude winds stronger hurricane

– Hurricane winds weaken with height

– Air in center of eye sinks downward

• Different names in different parts of the world:– Indian Ocean: cyclones

– Western Pacific Ocean: typhoons



• Form on west sides of oceans where warm water is concentrated

– Also off Pacific coast of Mexico – area of warm water isolated from cold California current by bend in coastline

– Not off coast of Brazil – Atlantic Ocean is too narrow, not enough warm water

• Form between 5o to 20o latitude, travel to higher latitudes



• Do not form along equator because Corioliseffect is zero

• Can not cross equator once formed – lose rotation

• Average of 84 tropical cyclones (hurricanes, typhoons, cyclones) form each year

– About 10 in north Atlantic Ocean, Caribbean Sea, Gulf of Mexico


Figure 11.11 Hurricane Origins


Hurricane Damage Potential

• Strength assessed by Saffir-Simpson scale– Category 1: wind damages trees and unanchored mobile

homes

– Category 2: winds blow down trees, major damage to mobile homes, some roofs

– Category 3: winds blow down large trees, strip foliage, destroy mobile homes, damage small buildings

– Category 4: all signs blown down, heavy damage to buildings, major damage to coastal buildings, flooding extends inland

– Category 5: severe damage to buildings, major damage to buildings less than 5 m above sea level and within 500 m of shoreline, small buildings overturned and blown away


TABLE 11.1 Saffir-Simpson Hurricane Damage Potential Scale

Barometric Pressure (millibars)

Barometric Pressure (inches)

Wind Speed (km/hr)

Wind Speed(mph)

Storm surge

(meters)

Storm surge(feet)

Damages

Category 1 ≥980 Over28.92 119-154 74-95 1.2-1.5 4-5 Minimal

Category 2 965-979 28.50-28.91 155-178 96-110 1.8-2.4 6-8 Moderate

Category 3 945-964 27.91-28.49 179-210 111-130 2.7-3.7 9-12 Extensive

Category 4 920-944 27.17-27.90 211-250 131-155 4-5.5 13-18 Extreme

Category 5 <920 Less than 27.17

>250 Over 155 >5.5 Over 18 Catastrophic


North Atlantic Ocean Hurricanes

• From 851 to 2006: U.S. Gulf and Atlantic coastlines hit by 279 hurricanes, three category 5 and 18 category 4

• Most form in late summer when sea surface temps are warmest


CategoryMaximum (Frequency

(Year))Minimum (Frequency

(Year))

Tropical Storms andHurricanes

28 (2005) 4 (1983)

Hurricanes 15 (2005) 2 (2013)

Major hurricanes (Winds > 110 mph)

8 (1950) 0 many times (e.g., 2013)

U.S. landfalling tropical storms and hurricanes

8 (1916) 1 many times (e.g., 1997)

U.S. landfalling hurricanes 6 (1985, 2004, 2005) 0 many times (e.g., 2013)

U.S. landfalling majorhurricanes

4 (2005) 0 many times (e.g., 2014)

Table 11.3 North Atlantic Tropical storms and Hurricanes, 1851-2014


North Atlantic Ocean Hurricanes: Cape Verde-type Hurricanes

• Usually begin as easterly waves moving west away from Africa

• May gain tropical storm status near Cape Verde Islands

• Blown westward with trade winds, gaining energy from warm seawater

• Movement curves northward due to Coriolis effect upon reaching western Atlantic


North Atlantic Ocean Hurricanes: Andrew,

August 1992 (1 of 2)

• Began as thunderstorms over West Africa, August 13

• Moved out over Atlantic Ocean as rotating low-pressure air mass

• Intensified into tropical storm by August 17

• Reached western Atlantic on August 21 as upper-level winds died down, allowing clouds and winds to build, and as high pressure to the north forced Andrew over warmer water to the west

• August 22: hurricane strength

• August 23: northern Bahamas, wind speeds of 240 km/hr


North Atlantic Ocean Hurricanes: Andrew, August 1992 (2 of 2)

• August 24: crossed southern Florida with 25-mile wide path over homes of 350,000 people, with winds of 250 km/hr, gusts up to 282 km/hr, vortices up to 320 km/hr

• Killed 33 people, destroyed 80,000 buildings

• Moved across Gulf of Mexico regaining energy

• Hit Louisiana with 190 km/hr winds on August 26

• Killed additional 15 people

• Spent remaining energy in heavy rains over Mississippi

• $35 billion in damages, most destructive in U.S. history

– Much of damage was result of poor construction


Figure 11.15 North Atlantic Ocean Hurricanes


Global Tropical Cyclone Paths

• Main influences on hurricane paths:

–Trade winds blow cyclones west

–Coriolis effect adds curve to right


Figure 11.12 Tracks of all Tropical Cyclones, 1985-2005


North Atlantic Ocean Hurricanes: Hurricane Paths

• Influences on hurricane paths:

– Size, position of Bermuda High: North Atlantic high pressure zone

▪ Small, to the north: hurricanes miss coastlines

▪ Strong, extensive: guides hurricanes along east coast of U.S.

▪ South: guides hurricanes to Gulf of Mexico


Hurricane Path Influences

• Bermuda High part of North Atlantic Oscillation(NAO): decade shifting of atmospheric pressures over ocean

– 1950s: east coast of North America hit by Category 3+ hurricanes

– 1960s, 1970s: Gulf coast hit by hurricanes


Figure 11.18 Hurricane Path Influences


North Atlantic Ocean Hurricanes: Caribbean Sea- and Gulf of Mexico- Type Hurricanes

• Form at Intertropical Convergence Zone (ITCZ), where trade winds meet

• Location of ITCZ moves with migration of the Sun

• ITCZ located south of equator in Northern Hemisphere’s winter and north of equator in Northern Hemisphere’s summer

• Low-pressure area forms where air flows converge thunderstorms hurricane


North Atlantic Ocean Hurricanes: Hurricane Mitch, October 1998 (1 of 2)

• October 22: tropical depression 13 at ITCZ in Caribbean

• 18 hours later: Tropical Storm Mitch

• 36 hours later: Hurricane Mitch

• October 26: one of strongest category 5 hurricanes

– Sustained winds of 290 km/hr, gusts greater than 320 km/hr

– Winds over 250 km/hr for 15 consecutive hours


North Atlantic Ocean Hurricanes: Hurricane Mitch, October 1998 (2 of 2)

• Heading toward Cuba then veered to Central America

• October 27: stalled off coast of Honduras, winds slowed down to tropical storm strength, but absorbed enormous amounts of water from warm ocean

• October 30: landfall in Central America, tremendous amounts of rain in Honduras and Nicaragua

– Three-day rainfall totals up to 2 m

– About 6,500 people killed in Honduras, about 3,800 people killed in Nicaragua, many by mudflows of pyroclastic material

– Second deadliest hurricane in history of Americas



Hurricane Forecasts • Increased number of storms in North Atlantic region can be

forecast based on:



Hurricane Forecasts• Annual probability of a named storm forming



Hurricane Forecasts• Percent probability of a hurricane hitting the coast.


TABLE 11.4 Hurricane Landfalls on U.S. Coastline, 1851-2014

State Hurricane Hits

Florida 114

Texas 64

Louisiana 58

North Carolina 53

South Carolina 30

Alabama 27

Georgia 23

Mississippi 19

New York 13

Massachusetts 11

Connecticut 11

Virginia 10

Data Source: NOAA.


TABLE 11.5 Hurricane Name Lists for the North Atlantic Basin Seasons, 2015-2020

(1 of 2)2015 2016 2017 2018 2019 2020

Ana Alex Arlene Alberto Andrea Arthur

Bill Bonnie Bret Beryl Barry Bertha

Claudette Colin Cindy Chris Chantal Cristobal

Danny Danielle Don Debby Dorian Dolly

Erika Earl Emily Ernesto Erin Edouard

Fred Fiona Franklin Florence Fernand Fay

Grace Gaston Gert Gordon Gabrielle Gonzalo

Henri Hermine Harvey Helene Humberto Hanna

Ida Ian Irma Isaac Imelda Isaias

Joaquin Julia Jose Joyce Jerry Josephine


TABLE 11.5 Hurricane Name Lists for the North Atlantic Basin Seasons, 2015-2020 (2 of 2)

2015 2016 2017 2018 2019 2020

Kate Karl Katia Kirk Karen Kyle

Larry Lisa Lee Leslie Lorenzo Laura

Mindy Matthew Maria Michael Melissa Marco

Nicholas Nicole Nate Nadine Nestor Nana

Odette Otto Ophelia Oscar Olga Omar

Peter Paula Philippe Patty Pablo Paulette

Rose Richard Rina Rafael Rebekah Rene

Sam Shary Sean Sara Sebastien Sally

Teresa Tobias Tammy Tony Tanya Teddy

Victor Virginie Vince Valerie Van Vicky

Wanda Walter Whitney William Wendy Wilfred


Decade of the Naughts – 2000 to 2009

• 2004: Florida hit by four hurricanes, Japan hit by 10 typhoons, first documented hurricane in South Atlantic hit Brazil

• 2005: Hurricane records broken in North Atlantic basin

• Increase due to human activity or natural variation?

• Total energy release by hurricanes is higher, probably due to increasing sea-surface temperatures and increased water vapor in lower atmosphere, possibly due to global warming


Table 11.6 Records Made During the 2005 Atlantic Hurricane Season

Most Numerous

28 named storms (old record: 21 in 1933)

15 hurricanes (old record: 12 in 1969)

4 major hurricanes hit the United States (old record:3 in 1909 1933 1954 2004

7 tropical storms before August 1 (old record: 5 in 1997)

Costliest

U.S. hurricane: Katrina

Mexican hurricane: Wilma


North Atlantic Ocean Hurricanes: Hurricane Damages

• Hurricane deaths are down in recent decades

• Hurricane damages are up

– Larger, more expensive homes on coastlines

• Destruction and deaths caused by:

–Winds

–Storm surges

–Heavy rains and inland flooding


TABLE 11.7 The 13 Deadliest Hurricanes in the United States, 1900-2014 (1 of 2)

When Where Number of Death

8 September 1900 Galveston, Texas 8,000

Mid-September 1928 South Florida—Lake Okeechobee 2,500

29 August 2005 Hurricane Katrina—Louisiana/Mississippi 1,836

Mid-September 1919 Florida Keys/Corpus Christi, Texas 600

29 September 1915 New Orleans, Louisiana 600

27 June 1957 Hurricane Audrey—Morgan City, Louisiana 416


TABLE 11.7 The 13 Deadliest Hurricanes in the United States, 1900-2014 (2 of 2)

When Where Number of Death

2 September 1935 Florida Keys 408

14-15 September 1944 East Coast Virginia to Massachusetts 390

Mid-September 1926 Miami, Florida/Alabama 372

21 September 1909 Grand Isle, Louisiana 350

17 August 1915 Galveston, Texas 275

21 September 1938 New England, especially Rhode Island 256

17-18 August 1969 Hurricane Camille-Mississippi 256


TABLE 11.9 The 22 Costliest Hurricanes Striking the United States, 1915-2014 (in 2010 US$) (1 of 2)

When Where Damage in Billions

Hurricane Category

2005 LA/MS—Katrina 106 3

2012 NJ/NY—Sandy 60 1

1992 FL—Andrew 46 5

2008 TX—Ike 28 2

2005 FL—Wilma 21 3

2004 FL/AL—Ivan 20 3

2004 FL—Charley 16 4

2011 NC/NJ/NY—Irene 15 1

1989 SC—Hugo 14 4

1972 FL/NE US—Agnes 12 1

2005 TX—Rita 12 3

1965 FL/LA—Betsy 11 3

2001 TX—Allison 11 TS


TABLE 11.9 The 22 Costliest Hurricanes Striking the United States, 1915-2014 (in 2010 US$) (2 of 2)

When Where Damage in Billions

Hurricane Category

2004 FL—Frances 10 2

1999 E US—Floyd 9 2 9 2

1969 MS—Camille 9 5

2004 FL—Jeanne 8 3

1995 FL/AL—Opal 8 3

1955 NE US—Diane 7 1

1979 AL/MS—Frederic 7 3

1938 New England 6 3

1996 NC—Fran 6 3


North Atlantic Ocean Hurricanes: Storm Surge Hazards

• Rise in sea level under storm due to:

– Winds push water ashore to pile up above normal levels, especially on right-hand side of storm – highest wind velocities

▪ In Northern Hemisphere, highest storm surge occurs 15-30 km to right of path of eye

– Low atmospheric pressure causes water to mound up under eye of hurricane

– Also large waves blown by hurricane winds

– Also sometimes already high astronomical tides


North Atlantic Ocean Hurricanes: Heavy Rains and Inland Flooding

• After moving on land, no more water vapor is absorbed into hurricane, so it loses strength

• Precipitation of massive volume of water in dissipating hurricane can cause massive flooding and deaths


TABLE 11.10 U.S. Hurricane Deaths, 1970-1999

Inland flooding 59%

Wind 12

Storm surge 12

Offshore 11

Tornado 4

Other 2

100%

Source : Tropical Cyclones & inland Flooding (2001); NOAA


Hurricanes and the Gulf of Mexico Coastline

Galveston, Texas, September 1900

• Deadliest natural disaster in U.S. history

• Galveston – wealthiest Texas city – 38,000 residents given warning of hurricane but many did not evacuate

• Category 4 hurricane – at high tide, with 200 km/hr winds

• Highest point on island flooded to 0.3 m

• 8,000 people killed, but many survived 10 m waves by crowding in lighthouse

• City constructed sea wall, brought in sand to elevate land

• 1915 hurricane killed another 275 people


Hurricane Katrina (1 of 2)

• August 24, 2005: Tropical air mass over Bahamas first catalogued as Katrina

• August 25, 2005: Grew to hurricane two hours before crossing Florida, lost strength but grew again rapidly over Gulf of Mexico double size, wind

speeds 280 km/hr

• August 26, 2005: models forecast 17% chance of direct hit to New Orleans

• August 27, 2005: Warnings issued, residents began to flee

• August 28, 2005: Mandatory evacuation ordered for 1.2 million residents, all roads exit New Orleans


Hurricane Katrina (2 of 2)

• August 29, 2005:

– Came ashore east of New Orleans, wind speeds of 195 mph

– Pushed in enough water to breach levees, overflow canals and flood 80% of low-lying New Orleans

– 1,800 of 100,000 residents who did not evacuate were killed

– Deadliest natural disaster since 1928 Okeechobee hurricane


Figure 11.34 Hurricane Katrina


Hurricane Katrina: Were the Katrina-Caused Deaths and Destruction a

Surprise? • Hurricane like Katrina was anticipated for

years

– Special reports in New Orleans Times Picayune in 2002, among others

• September 2004: Hurricane Ivan narrowly missed hitting New Orleans, after massive evacuation of city (practice run before Katrina, but same mistakes were repeated)


Hurricane Katrina: New Orleans-Can This Setting Be Protected? (1 of 2)

• Water and floods have always been part of city life, three centuries of floods from river and hurricanes

• Billions of dollars spent on levees

• City built on delta: loose mixture of sand, mud, and water deposited by Mississippi River


Hurricane Katrina: New Orleans-Can This Setting Be Protected? (2 of 2)

• Deltas naturally subside city has

subsided to 6 m below sea level and continues to subside

• Levees prevent flooding, therefore also prevent deposition of new layers of sand and mud that would build up land level

• Creates bowl, with lake and river water levels higher than city land

• Subsidence will continue no easy

solutions


Figure 11.37


The Evacuation Dilemma

• Satellite photos allow warning before hurricane makes landfall, people can evacuate out of way

• Almost 50 million people live in Atlantic Ocean or Gulf of Mexico coastline counties, population growth faster than construction of new roads or bridges

– Aided by assurance of federal disaster assistance

• Warning of 1999 Hurricane Floyd hitting South Carolina created massive gridlock leaving people exposed on roads

– Hurricane Floyd hit North Carolina instead

• Evacuation dilemma: estimated 72 hours to evacuate most cities

• Hurricane path not well known 72 hours in advance


Reduction of Hurricane Damages (1 of 2)

Building Codes

• After many manufactured homes destroyed by 1992 Hurricane Andrew, tougher building codes enacted – new manufactured homes survived four hurricanes of 2004

Roofs

• First step in destroying building is often to lift off roof

• Prevention by:

– Elimination or strengthening of eaves

– Strap roofs to walls

– Ban stapled asphalt roofing sheets on plywood

Impact of Wind-borne Debris

• Windows of shatter-proof glass or protected by shutters or plywood

• Remove loose objects outside


Reduction of Hurricane Damages (2 of 2)

Land-Use Planning

• Use low-lying coastal land for parks, farm fields, golf courses, nature preserves, etc., where flooding is not damaging

Coastal Development Restrictions

• Current building boom on shorelines

• Thousands of new homes built since last hurricane strike

• FEMA estimates next 60 years: 25% houses within 150 m of shoreline will fall into water during some hurricane, without mitigating actions


Figure 11.40

Hurricane Proofing a House: Sit atop pilings Allow water to flow below house Bolted steel beam construction No eaves Solid, heavy roof


Global Rise in Sea Level

• Global rise of ~1 ft in 20th century, probably 3 ft or more in 21st century

• Can move beaches inland by 1,000 ft in low-lying areas

• Continuing buildup of houses along coastline is just asking for trouble


Figure 11.41


Hurricanes and the Pacific Coastline

• 15% of Earth’s tropical cyclones: offshore southern Mexico, Guatemala, El Salvador

• Why is Pacific coastline hit by fewer hurricanes?

– Trade winds blow hurricanes west out to sea

– Cold California current from Alaska reduces energy available for hurricanes

Hurricane Iniki, September 1992

• Hawaiian Islands at northern edge of hurricane-generating warm waters, hit by storms formed to the southeast

• Iniki: category 4 storm tore across Kauai with 210 km/hr sustained winds and gusts of 260 km/hr

• Damaged all buildings, cost island economy $2 billion


Cyclones and Bangladesh

• Seven of world’s nine most deadly weather events in 20th century were cyclones hitting densely populated Bangladesh – low-lying sediments of deltas of Ganges and Brahmaputra Rivers, 1/3 below 6 m elevation

• In average year, 20% of country submerged in floods

• 1970 cyclone during full Moon high tides brought surge of 7 m, winds of 235 km/hr 300,000

people killed

• 1991 cyclone with 6 m surge, 235 km/hr winds killed 140,000 people

• Population of Bangladesh is expected to double in next 30 years

ch 11 hurricanes · • large tropical cyclones • heat engines converting heat of tropical ocean...

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