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Chapter 12Chapter 12

Tropical Weather SystemsTropical Weather Systems

AMS Weather StudiesAMS Weather Studies Introduction to Atmospheric Science, 4Introduction to Atmospheric Science, 4 thth Edition Edition

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Case-In-PointCase-In-Point Hurricane Katrina – 28 August 2005Hurricane Katrina – 28 August 2005

– Devastated the Gulf Coast of Louisiana and Mississippi; New Orleans Devastated the Gulf Coast of Louisiana and Mississippi; New Orleans experienced catastrophic floodingexperienced catastrophic flooding

– 33rdrd most intense landfalling U.S. hurricane most intense landfalling U.S. hurricane– Claimed 1,300 lives and is the most destructive hurricane in terms of Claimed 1,300 lives and is the most destructive hurricane in terms of

economic losseconomic loss– New Orleans topography made the city particularly vulnerableNew Orleans topography made the city particularly vulnerable

The city occupies a bowl between the Mississippi River and Lake The city occupies a bowl between the Mississippi River and Lake Pontchartrain, much of which is up to 1.8 m (6 ft) below sea levelPontchartrain, much of which is up to 1.8 m (6 ft) below sea level

New Orleans relies on levees and pumps to keep water outNew Orleans relies on levees and pumps to keep water out Levee system was breached, pumps failed, and city was flooded to depths Levee system was breached, pumps failed, and city was flooded to depths

of up to 6 m (20 ft)of up to 6 m (20 ft)– New Orleans residents were warned in advance, but thousands did New Orleans residents were warned in advance, but thousands did

not evacuatenot evacuate– Katrina was followed by Hurricane Rita less than a month laterKatrina was followed by Hurricane Rita less than a month later

Landfall was well to the west of New Orleans (near Sabine Pass, TX), but Landfall was well to the west of New Orleans (near Sabine Pass, TX), but flood waters up to 1.5 m (5 ft) deep spread over parts of the city due to flood waters up to 1.5 m (5 ft) deep spread over parts of the city due to new breaks in the leveesnew breaks in the levees

– Hurricane Gustav hit the Gulf Coast in 2008, causing $4.3 billion in Hurricane Gustav hit the Gulf Coast in 2008, causing $4.3 billion in damagedamage

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What conditions are required for the What conditions are required for the development of tropical cyclones?development of tropical cyclones?– This chapter will describe:This chapter will describe:

Weather in the tropicsWeather in the tropics Characteristics of tropical cyclonesCharacteristics of tropical cyclones Geographical and seasonal distributionGeographical and seasonal distribution Associated hazardsAssociated hazards Tropical cyclone life cycleTropical cyclone life cycle Forecasting effortsForecasting efforts Unsuccessful experiments to modify these stormsUnsuccessful experiments to modify these storms

Driving QuestionDriving Question

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Weather in the TropicsWeather in the Tropics The tropics is the belt between the Tropic of Cancer (23.5 degrees N) The tropics is the belt between the Tropic of Cancer (23.5 degrees N)

and the Tropic of Capricorn (23.5 degrees S)and the Tropic of Capricorn (23.5 degrees S) Weather exhibits very little seasonal variation with uniformly high Weather exhibits very little seasonal variation with uniformly high

temperaturestemperatures Diurnal temperature variation is typically greater than the range of Diurnal temperature variation is typically greater than the range of

monthly mean temperatures over the course of a yearmonthly mean temperatures over the course of a year No fronts or frontal weatherNo fronts or frontal weather

– Air masses are uniformly warm and humidAir masses are uniformly warm and humid Thunderstorm activityThunderstorm activity

– Thunderstorms may align in tropical non-squall clustersThunderstorms may align in tropical non-squall clusters– More intense cells (tropical squall clusters) can form that look like middle More intense cells (tropical squall clusters) can form that look like middle

latitude squall lineslatitude squall lines– ITCZ stimulates thunderstorm activity and follows the sun, so that summer is ITCZ stimulates thunderstorm activity and follows the sun, so that summer is

the rainy season and winter is the dry seasonthe rainy season and winter is the dry season Very little horizontal pressure gradientVery little horizontal pressure gradient

– Isobaric analysis is of little valueIsobaric analysis is of little value– Streamline analysis is used insteadStreamline analysis is used instead

A streamline is a line drawn on a map that is parallel to the wind directionA streamline is a line drawn on a map that is parallel to the wind direction Can be used to identify regions of divergence and convergence, such as that Can be used to identify regions of divergence and convergence, such as that

associated with an easterly waveassociated with an easterly wave

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Hurricane CharacteristicsHurricane Characteristics Definition – an intense cyclone that originates over Definition – an intense cyclone that originates over

tropical ocean waters, usually in late summer to tropical ocean waters, usually in late summer to early fall and has a maximum sustained wind speed early fall and has a maximum sustained wind speed ≥≥119 km per hr (74 mph)119 km per hr (74 mph)

Contrast with an Extra-tropical CycloneContrast with an Extra-tropical Cyclone– No associated fronts or frontal weather due to its origin No associated fronts or frontal weather due to its origin

over uniformly warm and humid conditionsover uniformly warm and humid conditions– Sea level pressure and steep horizontal air pressure Sea level pressure and steep horizontal air pressure

gradient are typically greater than that of an extra-tropical gradient are typically greater than that of an extra-tropical cyclonecyclone

– A hurricane is a much smaller systemA hurricane is a much smaller system– A mature hurricane is a warm-core low whose circulation A mature hurricane is a warm-core low whose circulation

weakens with altitude; an extra-tropical cyclone is a cold-weakens with altitude; an extra-tropical cyclone is a cold-core low whose circulation strengthens with altitudecore low whose circulation strengthens with altitude

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Hurricane CharacteristicsHurricane Characteristics The eye is at the center of a hurricaneThe eye is at the center of a hurricane

– Almost cloudless skies, subsiding air, light windsAlmost cloudless skies, subsiding air, light winds– Diameter ranging from 10 to 65 km (6 to 40 mi)Diameter ranging from 10 to 65 km (6 to 40 mi)– Eye shrinks as hurricane intensifiesEye shrinks as hurricane intensifies

The eye wall (borders the eye of a mature storm)The eye wall (borders the eye of a mature storm)– Ring of cumulonimbus clouds that produce heavy rains and very Ring of cumulonimbus clouds that produce heavy rains and very

strong windsstrong winds– The most dangerous and potentially most destructive part of a The most dangerous and potentially most destructive part of a

hurricane is the eye wall on the side of the advancing system where hurricane is the eye wall on the side of the advancing system where the wind blows in the same direction as the storm’s forward motionthe wind blows in the same direction as the storm’s forward motion In the Northern Hemisphere, this occurs on the right side of the In the Northern Hemisphere, this occurs on the right side of the

hurricane when facing in the direction of the system’s forward motionhurricane when facing in the direction of the system’s forward motion

Cloud bands spiral inward towards the eye wall and produce Cloud bands spiral inward towards the eye wall and produce heavy convective showers and hurricane-force windsheavy convective showers and hurricane-force winds

At high altitudes, cirrus or cirrostratus spiral outwardAt high altitudes, cirrus or cirrostratus spiral outward

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Hurricane CharacteristicsHurricane Characteristics

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Hurricane CharacteristicsHurricane Characteristics

The eye wall of Hurricane Katrina on 28 The eye wall of Hurricane Katrina on 28 August 2005 while the storm was over the August 2005 while the storm was over the

Gulf of MexicoGulf of Mexico

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Where and WhenWhere and When Necessary conditions for formation:Necessary conditions for formation:

– Relatively high sea surface temperatures (SST)Relatively high sea surface temperatures (SST) SST of at least 26.5 SST of at least 26.5 °°C (80 C (80 °°F) through an ocean depth of 45 m (150 ft) F) through an ocean depth of 45 m (150 ft)

or moreor more Sustains circulation by the latent heat released when water vapor, Sustains circulation by the latent heat released when water vapor,

evaporated from the ocean surface, is conveyed upward and condensesevaporated from the ocean surface, is conveyed upward and condenses Strong tropical cyclone winds can induce Ekman transport and lead to Strong tropical cyclone winds can induce Ekman transport and lead to

lower SSTlower SST Cyclones may intensify over warm-core rings and weaken over cold-core Cyclones may intensify over warm-core rings and weaken over cold-core

ringsrings SST requirement makes formation seasonalSST requirement makes formation seasonal

– Most Atlantic hurricanes develop in late summer and early autumn Most Atlantic hurricanes develop in late summer and early autumn when ocean surface waters are warmestwhen ocean surface waters are warmest

– Official season runs from 1 June to 30 NovemberOfficial season runs from 1 June to 30 November– Peak threat to U.S. coastline is from mid-August to late OctoberPeak threat to U.S. coastline is from mid-August to late October

– Adequate Coriolis EffectAdequate Coriolis Effect With rare exception, tropical cyclones do not form within 5 degrees of the With rare exception, tropical cyclones do not form within 5 degrees of the

equatorequator– Weak vertical wind shearWeak vertical wind shear

Allows cluster of cumulonimbus to formAllows cluster of cumulonimbus to form Wind shear would tear these apartWind shear would tear these apart

– Relatively humid air in the mid-troposphereRelatively humid air in the mid-troposphere

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Tropical Cyclone Breeding GroundsTropical Cyclone Breeding Grounds

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Where and WhenWhere and When

Frequency of Atlantic basin tropical storm and hurricanesFrequency of Atlantic basin tropical storm and hurricanes

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Where and WhenWhere and When During El NiDuring El Niñño, Atlantic hurricanes are infrequent due to o, Atlantic hurricanes are infrequent due to

strong high altitude windsstrong high altitude winds Strong wind shear is the main reason why hurricanes rarely Strong wind shear is the main reason why hurricanes rarely

form off the coasts of South Americaform off the coasts of South America Worldwide average of 80 tropical cyclones per yearWorldwide average of 80 tropical cyclones per year

– ½ strengthen to hurricanes½ strengthen to hurricanes– The western Pacific Ocean is the most active areaThe western Pacific Ocean is the most active area

About 27 systems each season, about 17 of which intensity into About 27 systems each season, about 17 of which intensity into typhoons (~ 4 supertyphoons)typhoons (~ 4 supertyphoons)

Only hurricanes spawned in the tropical Atlantic, Caribbean Only hurricanes spawned in the tropical Atlantic, Caribbean and Gulf of Mexico pose a serious threat to coastal North and Gulf of Mexico pose a serious threat to coastal North AmericaAmerica– Average – 10.6 named tropical storms, 6 become hurricanes (2.4 Average – 10.6 named tropical storms, 6 become hurricanes (2.4

major hurricanes), 2.5 hurricanes strike U.S. coast each yearmajor hurricanes), 2.5 hurricanes strike U.S. coast each year– 2005 season set a record with 27 named tropical storms2005 season set a record with 27 named tropical storms– Every Atlantic/Gulf coast state from TX to ME has been hitEvery Atlantic/Gulf coast state from TX to ME has been hit

FL is most hurricane prone, TX 2FL is most hurricane prone, TX 2ndnd, LA 3, LA 3rdrd

– The Pacific coast is rarely a hurricane target due to NE tradesThe Pacific coast is rarely a hurricane target due to NE trades– The Hawaiian Islands are sometimes threatenedThe Hawaiian Islands are sometimes threatened

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Life Cycle of a HurricaneLife Cycle of a Hurricane

Tropical DisturbanceTropical Disturbance– An organized cluster of An organized cluster of

cumulonimbus clouds over cumulonimbus clouds over tropical seas that has a tropical seas that has a surface center of low surface center of low pressure; usually triggered pressure; usually triggered by the ITCZby the ITCZ

– Easterly WaveEasterly Wave A ripple in the tropical A ripple in the tropical

easterlies featuring a weak easterlies featuring a weak trough of low pressuretrough of low pressure

Forms over East Africa and Forms over East Africa and propagates westwardpropagates westward

Precursors of ~ 65% of Precursors of ~ 65% of named Atlantic tropical named Atlantic tropical cyclonescyclones

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Life Cycle of a HurricaneLife Cycle of a Hurricane

Tropical DisturbanceTropical Disturbance– Only a small percentage of convective cloud clusters in the tropical Only a small percentage of convective cloud clusters in the tropical

Atlantic evolve into full-blown hurricanesAtlantic evolve into full-blown hurricanes Subsidence of air on the eastern flank of the Bermuda-Azores Subsidence of air on the eastern flank of the Bermuda-Azores

anticyclone and trade-wind inversion inhibit deep convectionanticyclone and trade-wind inversion inhibit deep convection Vertical wind shear is usually too greatVertical wind shear is usually too great Atmospheric conditions that inhibit cyclone formation appear to be Atmospheric conditions that inhibit cyclone formation appear to be

associated with the Sahara air layer (SAL), an elevated mass of dry, associated with the Sahara air layer (SAL), an elevated mass of dry, dusty, stable air originating over the Sahara Desert that travels many dusty, stable air originating over the Sahara Desert that travels many thousands of kilometers westward over the Atlanticthousands of kilometers westward over the Atlantic

– If conditions favor hurricane development, the surface air pressure If conditions favor hurricane development, the surface air pressure falls and a cyclonic circulation developsfalls and a cyclonic circulation develops Water vapor condenses within the storm, releases latent heat, and the Water vapor condenses within the storm, releases latent heat, and the

heated air rises. Expansional cooling of rising air triggers more heated air rises. Expansional cooling of rising air triggers more condensation and release of latent heatcondensation and release of latent heat

Rising temperatures in the storm’s core and divergence of air aloft Rising temperatures in the storm’s core and divergence of air aloft trigger a sharp drop in surface air pressure and increased surface trigger a sharp drop in surface air pressure and increased surface convergenceconvergence

If favorable conditions persist, cycle continues and the tropical If favorable conditions persist, cycle continues and the tropical disturbance intensifies and its winds strengthendisturbance intensifies and its winds strengthen

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Life Cycle of a HurricaneLife Cycle of a Hurricane

Tropical DepressionTropical Depression– Maximum sustained winds reach 37 km per hr Maximum sustained winds reach 37 km per hr

(23 mph) or higher(23 mph) or higher Tropical StormTropical Storm

– Winds reach at least 63 km per hr (39 mph)Winds reach at least 63 km per hr (39 mph)– Assigned a nameAssigned a name

HurricaneHurricane– Winds reach 119 km per hr (74 mph) or higherWinds reach 119 km per hr (74 mph) or higher

As storm weakens, it is downgraded by As storm weakens, it is downgraded by reversing this classification systemreversing this classification system

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Life Cycle of a HurricaneLife Cycle of a Hurricane Tropical cyclone trajectories are Tropical cyclone trajectories are

often erratic, however, cyclones often erratic, however, cyclones typically initially drift westward typically initially drift westward and curve toward the north and and curve toward the north and northeast when they reach the northeast when they reach the western Atlanticwestern Atlantic

Upon reaching about 30 Upon reaching about 30 degrees N, a hurricane may degrees N, a hurricane may begin to acquire extra-tropical begin to acquire extra-tropical characteristics as colder air is characteristics as colder air is drawn into the system and drawn into the system and fronts developfronts develop

Some hurricanes fueled by the Some hurricanes fueled by the warm Gulf Stream may maintain warm Gulf Stream may maintain tropical characteristics far up the tropical characteristics far up the Atlantic coastAtlantic coast

New England has been the New England has been the target of many strong hurricanestarget of many strong hurricanes

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Hurricane HazardsHurricane Hazards

Heavy rains and inland floodingHeavy rains and inland flooding– Freshwater flooding was responsible for 60% of deaths Freshwater flooding was responsible for 60% of deaths

from 1970 – 1999 attributed to tropical cyclones or their from 1970 – 1999 attributed to tropical cyclones or their remnantsremnants

Strong windsStrong winds– Responsible for 12% of deaths during the same periodResponsible for 12% of deaths during the same period

Tornadoes Tornadoes Storm surgeStorm surge

– Caused most of the 1,300 fatalities associated with Caused most of the 1,300 fatalities associated with Hurricane KatrinaHurricane Katrina

– Remains the most serious potential impact of a Remains the most serious potential impact of a landfalling hurricanelandfalling hurricane

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Hurricane HazardsHurricane Hazards

Inland FloodingInland Flooding– Rains are typically 13 - 25 Rains are typically 13 - 25

cm (5 - 10 in.)cm (5 - 10 in.)– Heavy rains persist as the Heavy rains persist as the

storm tracks inlandstorm tracks inland– Case study – Hurricane Case study – Hurricane

Agnes (1972)Agnes (1972) Rains accounted for most of Rains accounted for most of

the property damagethe property damage Devastating floods in mid-Devastating floods in mid-

Atlantic region, especially Atlantic region, especially central Pennsylvania, when central Pennsylvania, when heavy rain fell on already heavy rain fell on already saturated grounds and hilly saturated grounds and hilly terrainterrain

– Hurricane Mitch (1998), Hurricane Mitch (1998), Tropical Storm Alberto Tropical Storm Alberto (1994), and Tropical Storm (1994), and Tropical Storm Allison (2001) also caused Allison (2001) also caused devastating floodingdevastating flooding

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Hurricane HazardsHurricane Hazards

Inland FloodingInland Flooding– The image shows The image shows

radar-determined radar-determined cumulative rainfall cumulative rainfall over southeast over southeast Texas produced by Texas produced by the remnants of the remnants of Tropical Storm Tropical Storm AllisonAllison

– Allison ranks as the Allison ranks as the most deadly and most deadly and costly tropical storm costly tropical storm to strike the U.S. to strike the U.S. mainlandmainland

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Hurricane HazardsHurricane Hazards WindWind

– Wind pressure, the force per unit area caused by air in Wind pressure, the force per unit area caused by air in motion, increases with the square of the wind speedmotion, increases with the square of the wind speed

– Debris transported by wind increases damage potentialDebris transported by wind increases damage potential– Small but powerful whirlwinds (spin-up vortices) Small but powerful whirlwinds (spin-up vortices)

embedded in a hurricane’s circulation may be embedded in a hurricane’s circulation may be responsible for the most severe property damageresponsible for the most severe property damage

– Winds diminish rapidly upon storm landfallWinds diminish rapidly upon storm landfall Hurricane over land is no longer in contact with warm ocean Hurricane over land is no longer in contact with warm ocean

water, its energy sourcewater, its energy source Frictional resistance slows wind and shifts wind direction toward Frictional resistance slows wind and shifts wind direction toward

the center; causes the storm to fill and weakenthe center; causes the storm to fill and weaken The system may still produce tornadoes after making landfall, The system may still produce tornadoes after making landfall,

partially due to strong wind shear between the surface and aloftpartially due to strong wind shear between the surface and aloft

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Hurricane HazardsHurricane Hazards Storm surgeStorm surge

– A dome of ocean water 80 – 160 km (50 – 100 mi) wide that sweeps over A dome of ocean water 80 – 160 km (50 – 100 mi) wide that sweeps over the coastline near the hurricane’s landfallthe coastline near the hurricane’s landfall

– Caused by strong winds and low barometric pressure and is most likely on Caused by strong winds and low barometric pressure and is most likely on the side of the hurricane with onshore windsthe side of the hurricane with onshore winds

– Wind-driven waves on top of the dome of water, armed with floating debris, Wind-driven waves on top of the dome of water, armed with floating debris, are responsible for much of the structural damageare responsible for much of the structural damage

– Prior to 1970, was responsible for the majority of hurricane-related Prior to 1970, was responsible for the majority of hurricane-related fatalities. Awareness, warnings, and evacuation have generally been much fatalities. Awareness, warnings, and evacuation have generally been much better since then.better since then.

– From 1970 to 1999, there were only 6 storm surge deaths. Then there was From 1970 to 1999, there were only 6 storm surge deaths. Then there was Hurricane Katrina and the death and destruction caused by its surge.Hurricane Katrina and the death and destruction caused by its surge.

– 1895 unnamed hurricane killed an estimated 2,000, and left 20,000 to 1895 unnamed hurricane killed an estimated 2,000, and left 20,000 to 30,000 homeless due to the storm surge30,000 homeless due to the storm surge

– The most deadly U.S. natural disaster was the hurricane that hit Galveston, The most deadly U.S. natural disaster was the hurricane that hit Galveston, TX (1900) when 8,000 people perishedTX (1900) when 8,000 people perished

– Hurricane Camille (1969) produced a 7.3 m (24.3ft) surge at Pass Hurricane Camille (1969) produced a 7.3 m (24.3ft) surge at Pass Christian, MSChristian, MS

– East Pakistan (now Bangladesh) in 1970 – storm surge killed ~300,000East Pakistan (now Bangladesh) in 1970 – storm surge killed ~300,000

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Hurricane HazardsHurricane Hazards

What causes a storm surge?What causes a storm surge?– Strong onshore winds combined with low air pressureStrong onshore winds combined with low air pressure

Low air pressure causes the water to rise about 0.5 m for every Low air pressure causes the water to rise about 0.5 m for every 50 mb drop in pressure (or about 1 ft for every 1 in. of mercury 50 mb drop in pressure (or about 1 ft for every 1 in. of mercury drop in pressure)drop in pressure)

– The storm surge is superimposed on top of normal tidesThe storm surge is superimposed on top of normal tides– A surge of 1 – 2 m (3 – 6.5 ft) can be expected with a A surge of 1 – 2 m (3 – 6.5 ft) can be expected with a

weak hurricane; that of a violent hurricane may top 5 m weak hurricane; that of a violent hurricane may top 5 m (16.4 ft)(16.4 ft)

– The greatest potential for a surge occurs with strong The greatest potential for a surge occurs with strong onshore winds, a shallow sloping shoreline, during high onshore winds, a shallow sloping shoreline, during high tide, and in densely-populated areas lacking coastal tide, and in densely-populated areas lacking coastal buffersbuffers

– Storm surges are accurately predicted with a numerical Storm surges are accurately predicted with a numerical model called SLOSH (Sea, Lake, and Overland Surges model called SLOSH (Sea, Lake, and Overland Surges from Hurricanes)from Hurricanes)

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Storm SurgeStorm Surge

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Saffir-Simpson Hurricane Intensity ScaleSaffir-Simpson Hurricane Intensity Scale

Provides an estimate of potential coastal flooding and property Provides an estimate of potential coastal flooding and property damage from a hurricane landfalldamage from a hurricane landfall

Wind speed is the primary determining factor for a hurricane’s ratingWind speed is the primary determining factor for a hurricane’s rating Storm surge is just an estimateStorm surge is just an estimate

– It depends on underwater topography and other factors in the region of It depends on underwater topography and other factors in the region of landfalllandfall

Property damage rises rapidly with ratingProperty damage rises rapidly with rating– 100-300 times greater damage from a category 4 or 5 hurricane than a 100-300 times greater damage from a category 4 or 5 hurricane than a

category 1category 1 From 1901 to 2004, about 37% of landfalling hurricanes were classified From 1901 to 2004, about 37% of landfalling hurricanes were classified

as major (category 3 or above)as major (category 3 or above)

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Saffir-Simpson Hurricane Intensity ScaleSaffir-Simpson Hurricane Intensity Scale

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Saffir-Simpson Hurricane Intensity ScaleSaffir-Simpson Hurricane Intensity Scale

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Saffir-Simpson Hurricane Intensity ScaleSaffir-Simpson Hurricane Intensity Scale

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Trends in Hurricane FrequencyTrends in Hurricane Frequency The figure shows the The figure shows the

recent upward trend in the recent upward trend in the number of intense number of intense (category 4 and 5) (category 4 and 5) hurricanes worldwide, hurricanes worldwide, even though the overall even though the overall number of hurricanes number of hurricanes worldwide has declined worldwide has declined since the 1990ssince the 1990s

Most of the increased Most of the increased frequency occurred in the frequency occurred in the North Pacific, SW Pacific, North Pacific, SW Pacific, and Indian Ocean, with and Indian Ocean, with only a small increase in only a small increase in the North Atlanticthe North Atlantic

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Trends in Hurricane FrequencyTrends in Hurricane Frequency The North Atlantic is the The North Atlantic is the

only region of the globe only region of the globe where overall tropical where overall tropical cyclone activity has cyclone activity has increased recentlyincreased recently

Several factors contribute:Several factors contribute:– Higher SST in the tropical Higher SST in the tropical

Atlantic related to the Atlantic related to the Atlantic Multidecadal Atlantic Multidecadal Oscillation (AMO)Oscillation (AMO)

– An amplified ridge over the An amplified ridge over the central and eastern North central and eastern North AtlanticAtlantic

– Weaker vertical wind shear Weaker vertical wind shear in the deep tropics over the in the deep tropics over the central North Atlanticcentral North Atlantic

– Favorable African easterly Favorable African easterly jet streamjet stream

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Hurricane Threat to the SoutheastHurricane Threat to the Southeast The infrequency in major The infrequency in major

hurricanes during the 1970s and hurricanes during the 1970s and 1980s lulled many coastal 1980s lulled many coastal residents of the southeast U.S. residents of the southeast U.S. into a false sense of security into a false sense of security and encouraged coastal and encouraged coastal development and growthdevelopment and growth

In 2005, NOAA reported that the In 2005, NOAA reported that the coast is home to 53% of all coast is home to 53% of all AmericansAmericans

Population growth is most rapid Population growth is most rapid from Texas through the from Texas through the Carolinas, especially in FloridaCarolinas, especially in Florida

Public safety officials are Public safety officials are concerned about the trend concerned about the trend toward more Atlantic tropical toward more Atlantic tropical cyclonescyclones

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Hurricane Threat to the SoutheastHurricane Threat to the Southeast

Tracks of three of the four hurricanes that struck Florida in 2004Tracks of three of the four hurricanes that struck Florida in 2004

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Hurricane Threat to the SoutheastHurricane Threat to the Southeast Barrier islands are particularly at riskBarrier islands are particularly at risk

– A barrier island is an elongated, narrow A barrier island is an elongated, narrow accumulation of sand oriented parallel to the coast accumulation of sand oriented parallel to the coast and separated from the mainland by a lagoon, and separated from the mainland by a lagoon, estuary, or bayestuary, or bay

Padre Island in Texas is the longest in the U.S. Padre Island in Texas is the longest in the U.S. measuring more than 180 km (112 mi)measuring more than 180 km (112 mi)

– A constantly changing systemA constantly changing system Sea waves dissipate their energy by shifting the Sea waves dissipate their energy by shifting the

sands and modifying the shape of the islandsands and modifying the shape of the island Gradually migrate toward the mainlandGradually migrate toward the mainland Face an open ocean and absorb the brunt of ocean Face an open ocean and absorb the brunt of ocean

stormsstorms– Cities such as Atlantic City, NJ, Miami Beach, FL, Cities such as Atlantic City, NJ, Miami Beach, FL,

and Virginia Beach, VA are built entirely on barrier and Virginia Beach, VA are built entirely on barrier islandsislands

– The photographs show a barrier island at Pine The photographs show a barrier island at Pine Beach, FL before and after Hurricane Ivan caused Beach, FL before and after Hurricane Ivan caused a breacha breach

– Evacuation becomes critical here, as well as other Evacuation becomes critical here, as well as other coastal areascoastal areas

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EvacuationEvacuation Effectiveness of coastal evacuation Effectiveness of coastal evacuation

plans was tested in 1985 when plans was tested in 1985 when category 3 Hurricane Elena (bottom category 3 Hurricane Elena (bottom figure) followed an erratic path over figure) followed an erratic path over the Gulf of Mexicothe Gulf of Mexico

The potential downside of evacuation The potential downside of evacuation was illustrated by Hurricane Floyd was illustrated by Hurricane Floyd (1999), a very large hurricane (1999), a very large hurricane approaching the Southeastapproaching the Southeast– 2 million were evacuated and massive 2 million were evacuated and massive

gridlock occurredgridlock occurred Greater uncertainty with forecast Greater uncertainty with forecast

track translates into a broader track translates into a broader evacuation zone and greater evacuation zone and greater economic losseseconomic losses– Cost of evacuation amounts to about $1 Cost of evacuation amounts to about $1

million per mile of coastlinemillion per mile of coastline– Vertical evacuation may be an optionVertical evacuation may be an option

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EvacuationEvacuation

Other strategies to Other strategies to minimize loss of life and minimize loss of life and property:property:– Stringent building codesStringent building codes– Preservation of mangrove Preservation of mangrove

swampsswamps– Elimination of federal Elimination of federal

floodplain insurancefloodplain insurance The photograph shows a The photograph shows a

home designed so that the home designed so that the first floor will give way to first floor will give way to storm-surge floodwaters. storm-surge floodwaters. The second and third floor The second and third floor living areas are supported living areas are supported by wooden beams driven by wooden beams driven deeply into the sanddeeply into the sand

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Long-Range Forecasting of Atlantic Long-Range Forecasting of Atlantic HurricanesHurricanes

Since the early 1980s, Prof. William M. Gray and his colleagues at Since the early 1980s, Prof. William M. Gray and his colleagues at Colorado State University have issued seasonal hurricane activity Colorado State University have issued seasonal hurricane activity forecasts for the Atlantic basinforecasts for the Atlantic basin– First forecast issued 6 months before the hurricane season and then First forecast issued 6 months before the hurricane season and then

updates are madeupdates are made– Original basis of forecasts was apparent linkage between the frequency of Original basis of forecasts was apparent linkage between the frequency of

hurricanes in the tropical Atlantic and rainfall in West Africahurricanes in the tropical Atlantic and rainfall in West Africa– Also factored in stratospheric quasi-biennial oscillation (QBO)Also factored in stratospheric quasi-biennial oscillation (QBO)– After this scheme didn’t work well for several years after giving skillful After this scheme didn’t work well for several years after giving skillful

results, they developed a new one based on empirical relationships results, they developed a new one based on empirical relationships between Atlantic Basin hurricane activity and a combination of atmospheric between Atlantic Basin hurricane activity and a combination of atmospheric factors in various parts of the world, including the QBOfactors in various parts of the world, including the QBO

– In order to improve skill, a modified statistical forecast scheme was recently In order to improve skill, a modified statistical forecast scheme was recently developed using data from 1950-2007, and first implemented in the developed using data from 1950-2007, and first implemented in the December 2007 forecastDecember 2007 forecast

NOAA has also issued a Seasonal Outlook for Atlantic basin hurricane NOAA has also issued a Seasonal Outlook for Atlantic basin hurricane activity since 1998activity since 1998– Gives probabilities of overall seasonal activity compared to normal, and Gives probabilities of overall seasonal activity compared to normal, and

likely ranges of named tropical cyclones, hurricanes, major hurricanes, and likely ranges of named tropical cyclones, hurricanes, major hurricanes, and Accumulated Cyclone Energy (ACE)Accumulated Cyclone Energy (ACE)

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Hurricane ModificationHurricane Modification

Project STORMFURY (1961-1983)Project STORMFURY (1961-1983)– Spurred by 6 destructive hurricanes that affected U.S. Spurred by 6 destructive hurricanes that affected U.S.

East Coast during the mid-1950sEast Coast during the mid-1950s– Working hypothesis: seeding hurricanes with silver Working hypothesis: seeding hurricanes with silver

iodide crystals would reduce wind strengthiodide crystals would reduce wind strength This was supposed to increase latent heat and enhance This was supposed to increase latent heat and enhance

convection just beyond the eye wallconvection just beyond the eye wall A new eyewall would then form farther out and the hurricane’s A new eyewall would then form farther out and the hurricane’s

circulation would theoretically weakencirculation would theoretically weaken

– Apparent modest successes were dismissed because Apparent modest successes were dismissed because convective clouds in hurricanes were found to have too convective clouds in hurricanes were found to have too little supercooled water for seeding to be effectivelittle supercooled water for seeding to be effective