Hurricanes

This chapter discusses:

1. Tropical cyclone and hurricane development, structure, and movement

2. Hurricane damages, warning systems, and naming conventions

Tropical Weather & Waves

• Tropical winds typically blow from the east, and when they encounter a slow moving trough of low pressure, called a tropical wave, the winds initially converge and lift to produce showers and thunderstorms.

• In the tropics, since pressure gradient are so weak, streamlines are used to depict the easterly (tropical) waves

• Rain showers are located behind the wave.

Structures and Sizes of Hurricanes

• Tropical cyclone (TC) is the international name for hurricane.

• TC typically forms from an organized mass of storms initially starting out as a tropical wave.

• The central area of broken clouds is called the eye, which is surrounded by an eye wall cloud and spiral rain bands, with a total diameter nearing 500 kilometers.

• Hurricanes can come in many sizes but general are on the order of the meso-alpha scale.

• Typhoon Tip (1979) was the largest storms with gale force winds (39 mph) that extended out for 675 miles (1087 km) in radius in the Northwest Pacific on 12 October, 1979.

• The smallest storm was Tropical Cyclone Tracy with gale force winds that only extended 30 miles (48 km) radius when it struck Darwin, Australia, on December 24, 1974.

Courtesy of the NWS

Hurricane Vertical Wind Profile

• The low pressure core of the hurricane is surrounded by several thunderstorms, each with updraft and downdraft cycles.

• The wind and moisture cycle is repeated as:

- surface moist air converges in a counterclockwise (in the northern hemisphere) pattern at the eye;

- rises to create high pressure aloft, condenses, precipitates, dries, diverges outward in a clockwise pattern, sinks, and warms.

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L

L

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3-D Radar Image and Horizontal Wind Profile of Hurricane

• Several key features of a hurricane are shown in this radar composite image, including overshooting clouds, the area of strongest echoes (heaviest rain), and the eyewall.

• Cloud tops within the eyewall can reach 16km (52,000 ft).

• Notice the cyclonic wind motion around a hurricane and the highest winds are locate within the eyewall.

Ingredients Needed for Hurricane Formation

• Surface Ocean Temperature > 26.5 °C (80 °F)

• Depth of the warm water > 200 m (600 ft)

• Forms between 5°- 20° (Coriolis effect is needed)

• Surface winds convergence (ITCZ)

• Rising motion (trade wind inversion = bad)

• Weak upper level wind (high pressure aloft)

During El Nino Events, upper-level winds over the Atlantic ocean are stronger.

Organized Convection Theory

• This theory explains that hurricane formation requires cold air above an organized mass of thunderstorms, where the release of latent heat warms the upper troposphere, creating high pressure aloft, which pushes air outward and causes a low to deepen at the surface.

• Air moving toward this low intensifies the cycle and the low pressure will deepen.

• The stronger winds will generate rougher seas which increase surface friction.

• The increase in friction causes the wind to converge and ascend around the center of the storm.

• This set of actions eventually forms a hurricane and is considered a feedback mechanism.

• Hurricane development process has been proposed similar to a heat engine cycle, fueled by warm moist input air and the release of heat when it converts to cool dry air.

• Hurricane is taken heat energy at the surface and transforming it into kinetic energy.

• Differences in the input and output temperatures determine the amount of work on the ocean and winds that is performed.

• The greater the difference, the stronger the tropical system.

• Hence, the warmer the ocean surface, the lower the minimum pressure, the stronger the wind speed.

Cold (Tropopause)

Warm and Moist (Sea Surface)

Temperature Difference

Hurricane Stages of Development

tropical disturbance (tropical wave) – a semi-organized mass of thunderstorms generally with a cyclonic wind shift; wind speed < 20 knots (< 23 mph).

tropical depression – an organized mass of thunderstorms with a weak low-level cyclonic circulation; wind speed ranges from 20 - 34 knots (23 - 39 mph).

tropical storm – a more organized system of thunderstorms with cyclonic low-level winds; wind speed ranges from 35 - 64 knots (40 - 74 mph).

hurricane - A well developed cyclonic system with winds exceeding 64 knots (> 74 mph).

Hurricanes vs. Extratropical Cyclones

• Extratropical Cyclones (ETC) are cold core lows.

• Intensify with height

• Hurricanes (TC) are warm core lows.

• Weaken with height

• Center of the storm:

• ETC – rising motion

• TC – sinking motion

• Isobars

• ETC – not as circular

• TC – circular and tighter

Hurricane Movement

• Global patterns of tropical cyclone formation and movement have been recorded on this figure, which notes regional names for these systems.

• Travel speeds for the hurricane my range from 10 to 50 knots, but they may also stall over a region and cause destructive flooding.

Erratic Paths of Hurricanes• Historical charts of hurricane

location may reveal erratic, and hard to predict, patterns of movement.

• As this figure shows, hurricanes may occasionally double back.

• Usually, once a tropical system enters into the middle latitudes, it turns to the northeast and increase in the system’s speed.

• Further, when removed from the ocean and without a moisture source to supply energy, they may still continue an inland journey.

• In the North Atlantic, on average 3 storms per year move inland and bring damaging winds and rain.

North Atlantic Hurricanes• Composite infrared

imagery of Hurricane Georges reveals the pattern of a seasonal threat for Central and North America coastlines.

• Tropical cyclones at the same latitude survive longer in the Atlantic than Pacific Ocean because of warmer Atlantic Ocean waters.

Annual average of tropical systems developing in the Atlantic basin and the numbers of those storms turning into

hurricanes.

Climatological Areas of Origin and Typical Hurricane Tracks by Month Over the Atlantic Ocean Basin

The average cumulative number of Atlantic and Eastern Pacific systems

• Eastern Pacific Basin tends to form more named systems, hurricanes, and more intense tropical storms.

• Most Eastern Pacific systems tend to move out to sea and have no adverse effect on society with the exception of rip currents along the coast.

Australian Hurricanes

Image credit: Navy Research Lab

• Cyclone Monica at peak intensity at 0130 GMT April 24, 2006, the strongest storm in 2006 Australia TC season-180 mph sustained winds with gusts of 215 mph, and an estimated central SLP of 879 mb pressure.

• Notice the clockwise rotation of tropical cyclone Monica.• Southern hemisphere low pressure systems spin clockwise.

Image credit: Navy Research Lab

• The Brazilian hurricane on March 26, 2004 was the first officially recorded tropical system in the south Atlantic.

• The surface winds were estimated about 65 knots (~75 mph).

• The South Atlantic is generally not a favorable environment where tropical cyclones can form where the water temperatures are generally too cool and the vertical wind shear too strong.

• It was unofficially named Catarina by the weather community.

Brazilian “Unnamed” Hurricane

Societal Impacts•During 2004 and 2005, 8 hurricanes made landfall over Florida and Gulf Coast states.

•Hurricane Ivan made landfall on 15 September 2004 with winds of 121 mph and a central pressure of 945 mb.

•The sea level along the Alabama coast rose to 16 ft above normal causing property damage over 14 billions.

Hurricane Damage & Warning

• Hurricanes have their highest wind speeds on the side where storm pushing winds amplify cyclonic, or counterclockwise, rotational winds.

• In coastal areas, flooding is aggravated by the hurricane low pressure triggering higher tides and Ekman transport piling up water.

• The combination of high water, high winds, and enhance transport of water creates a storm surge.

• Huge waves, high seas, and flooding cause the most damage with a land falling hurricanes and not the high winds.

Hurricane Watch & Warning

• The National Hurricane Center in Florida issues a hurricane watch 24 to 48 hours before a threatening storm arrives, and if it appears that the storm will strike within 24 hours, a hurricane warning is issued.

• While some consider the warning area too large, causing unneeded evacuation, such evacuations have saved many lives.

• Hurricane Hugo, with peak winds near 174 knots, caused tremendous damage.

Hurricane Saffir-Simpson Winds

• In 1989 Hugo caused nearly $7 billion in damages in the U.S., killing 49 in the Caribbean and United States.

• Current classification of hurricanes is based on their wind speed, however, and not on human or property damage.

• Hurricanes range from category 1 to 5, with winds of 64 to more than 135 knots.

Hurricane Scale

Hurricane Names and Cost

• Category 5 Hurricane Andrew (1992) was the costliest US storm, but it ranks as less intense than 1935 and 1969 hurricanes.

• Hurricane names are chosen from an alphabetical list of male and female names for the Atlantic and Pacific, some of which are retired if the storm was especially damaging.

Names for Atlantic and Eastern North Pacific tropical systems

Atlantic Ocean Basin Name List for Tropical Systems

Eastern Pacific Ocean Basin Name List for Tropical Systems

Likelihood for Landfall

• Between 1900 and 2010, only three category 5 hurricanes have made landfall along the Gulf or Atlantic.

• Numerous category 1, and less damaging storms, that do make landfall may not cause much damage, but bring needed rainfall.

Decade

Saffir-Simpson ScaleAll

1,2,3,4,5Major3,4,51 2 3 4 5

1851-1860 8 5 5 1 0 19 6

1861-1870 8 6 1 0 0 15 1

1871-1880 7 6 7 0 0 20 7

1881-1890 8 9 4 1 0 22 5

1891-1900 8 5 5 3 0 21 8

1901-1910 10 4 4 0 0 18 4

1911-1920 10 4 4 3 0 21 7

1921-1930 5 3 3 2 0 13 5

1931-1940 4 7 6 1 1 19 8

1941-1950 8 6 9 1 0 24 10

1951-1960 8 1 5 3 0 17 8

1961-1970 3 5 4 1 1 14 6

1971-1980 6 2 4 0 0 12 4

1981-1990 9 1 4 1 0 15 5

1991-2000 3 6 4 0 1 14 5

2001-2006 6 2 6 1 0 159 7

 

1851-2006 110 73 75 18 3 279 96

Average Per Decade 7.1 4.7 4.8 1.2 0.2 17.9 6.2

U.S. Hurricane Strikes by Decade

30 Costliest Contiguous U.S. Hurricanes from 1900 - 2006 (unadjusted)

RANK HURRICANE YEAR CATEGORY DAMAGE (U.S.)

1 KATRINA (SE FL, SE LA, MS) 2005 3 $81,000,000,000

2 ANDREW (SE FL/SE LA) 1992 5 26,500,000,000

3 WILMA (S FL) 2005 3 20,600,000,000

4 CHARLEY (SW FL) 2004 4 15,000,000,000

5 IVAN (AL/NW FL) 2004 3 14,200,000,000

6 RITA (SW LA, N TX) 2005 3 11,300,000,000

7 FRANCES (FL) 2004 2 8,900,000,000

8 HUGO (SC) 1989 4 7,000,000,000

9 JEANNE (FL) 2004 3 6,900,000,000

10 ALLISON (N TX) 2001 TS 5,000,000,000

11 FLOYD (Mid-Atlantic & NE U.S.) 1999 2 4,500,000,000

12 ISABEL (Mid-Atlantic) 2003 2 3,370,000,000

13 FRAN (NC) 1996 3 3,200,000,000

14 OPAL (NW FL/AL) 1995 3 3,000,000,000

15 FREDERIC (AL/MS) 1979 3 2,300,000,000

16 DENNIS (NW FL) 2005 3 2,230,000,000

17 AGNES (FL/NE U.S.) 1972 1 2,100,000,000

18 ALICIA (N TX) 1983 3 2,000,000,000

19 BOB (NC, NE U.S) 1991 2 1,500,000,000

19 JUAN (LA) 1985 1 1,500,000,000

21 CAMILLE (MS/SE LA/VA) 1969 5 1,420,700,000

22 BETSY (SE FL/SE LA) 1965 3 1,420,500,000

23 ELENA (MS/AL/NW FL) 1985 3 1,250,000,000

24 GEORGES (FL Keys, MS, AL) 1998 2 1,155,000,000

25 GLORIA (Eastern U.S.) 1985 3 900,000,000

26 LILI (SC LA) 2002 1 860,000,000

27 DIANE (NE U.S.) 1955 1 831,700,000

28 BONNIE (NC,VA) 1998 2 720,000,000

29 ERIN (NW FL) 1998 2 700,000,000

30 ALLISON (N TX) 1989 TS 500,000,000

30 ALBERTO (NW FL,GA,AL) 1994 TS 500,000,000

30 FRANCES (TX) 1998 TS 500,000,000

30 ERNESTO (FL,NC,VA) 2006 TS 500,000,000

30 Costliest Contiguous U.S. Hurricanes from 1900 - 2006 (adjusted for 2006 standard of living, population growth and wealth normalization)

RANK HURRICANE YEAR Category Damage (Millions)

1 SE Florida/Alabama 1926 4 $164,839

2 N Texas (Galveston) 1900 4 104,330

3 KATRINA (SE LA, MS, AL) 2005 3 85,050

4 N Texas (Galveston) 1915 4 71,397

5 ANDREW (SE FL/LA) 1992 5 58,555

6 New England 1938 3 41,122

7 SW Florida 1944 3 40,621

8 SE Florida/Lake Okeechobee 1928 4 35,298

9 DONNA (FL/Eastern U.S.) 1960 4 28,159

10 CAMILLE (MS/LA/VA) 1969 5 22,286

11 WILMA (S FL) 2005 3 21,630

12 BETSY (SE FL/LA) 1965 3 18,749

13 DIANE (NE U.S.) 1955 1 18,073

14 AGNES (NW FL, NE U.S.) 1972 1 18,052

15 HAZEL (SC/NC) 1954 4 17,339

16 CHARLEY (SW FL) 2004 4 17,135

17 CAROL (NE U.S.) 1954 3 16,940

18 IVAN (NW FL, AL) 2004 3 16,247

19 HUGO (SC) 1989 4 16,088

20 SE Florida 1949 3 15,398

21 CARLA (N & Central TX) 1961 4 14,920

22 SE Florida/Louisiana/Alabama 1947 4 14,406

23 NE U.S. 1944 3 13,881

24 S Texas 1919 4 13,847

25 SE Florida 1945 3 12,956

26 RITA (SW LA/N TX) 2005 3 11,865

27 FREDERIC (AL/MS) 1979 3 10,781

28 FRANCES (SE FL) 2004 2 10,168

29 NC/VA 1933 2 8,603

30 DORA (NE FL) 1964 2 8,066

30 Most Intense Contiguous U.S. Hurricanes from 1851 - 2006 (by lowest observed central pressure)

CATEGORY MINIMUM PRESSURE

RANK HURRICANE YEAR (at landfall) Millibars Inches

1 FL (Keys) 1935 5 892 26.35

2 CAMILLE (MS/SE LA/VA) 1969 5 909 26.84

3 KATRINA (SE LA, MS) 2005 3 920 27.17

4 ANDREW (SE FL/SE LA) 1992 5 922 27.23

5 TX (Indianola) 1886 4 925 27.31

6 FL (Keys)/S TX 1919 4 927 27.37

7 FL (Lake Okeechobee) 1928 4 929 27.43

8 DONNA (FL/Eastern U.S.) 1960 4 930 27.46

9 LA (New Orleans) 1915 4 931 27.49

9 CARLA (N & Central TX) 1961 4 931 27.49

11 LA (Last Island) 1856 4 934 27.58

11 HUGO (SC) 1989 4 934 27.58

13 FL (Miami)/MS/AL/Pensacola 1926 4 935 27.61

14 TX (Galveston) 1900 4 936 27.64

15 RITA (SW LA/N TX) 2005 3 937 27.67

16 GA/FL (Brunswick) 1898 4 938 27.70

16 HAZEL (SC/NC) 1954 4 938 27.70

18 SE FL/SE LA/MS 1947 4 940 27.76

19 N TX 1932 4 941 27.79

19 CHARLEY (SW FL) 2004 4 941 27.79

21 GLORIA (Eastern U.S.) 1985 3 942 27.82

21 OPAL (NW FL/AL) 1995 3 942 27.82

23 FL (Central) 1888 3 945 27.91

23 E NC 1899 3 945 27.91

23 AUDREY (SW LA/N TX) 1957 4 945 27.91

23 TX (Galveston) 1915 4 945 27.91

23 CELIA (S TX) 1970 3 945 27.91

23 ALLEN (S TX) 1980 3 945 27.91

29 New England 1938 3 946 27.94

29 FREDERIC (AL/MS) 1979 3 946 27.94

29 IVAN (AL, NW FL) 2004 3 946 27.94

29 DENNIS (NW FL) 2005 3 946 27.94

25 Deadliest Contiguous U.S. Hurricanes from 1851 - 2006 (causing 25 or greater fatalities)

RANK HURRICANE YEAR CATEGORY DEATHS

1 TX (Galveston) 1900 4 8000 a

2 FL (SE/Lake Okeechobee) 1928 4 2500 b

3 KATRINA(SE LA/MS) 2005 3 1500

4 LA (Cheniere Caminanda) 1893 4 1100-1400 c

5 SC/GA (Sea Islands) 1893 3 1000-2000 d

6 GA/SC 1881 2 700

7 AUDREY (SW LA/N TX) 1957 4 416 h

8 FL (Keys) 1935 5 408

9 LA (Last Island) 1856 4 400 e

10 FL (Miami)/MS/AL/Pensacola 1926 4 372

11 LA (Grand Isle) 1909 3 350

12 FL (Keys)/S TX 1919 4 287 j

13 LA (New Orleans) 1915 4 275 e

13 TX (Galveston) 1915 4 275

15 New England 1938 3 256

15 CAMILLE (MS/SE LA/VA) 1969 5 256

17 DIANE (NE U.S.) 1955 1 184

18 GA, SC, NC 1898 4 179

19 TX 1875 3 176

20 SE FL 1906 3 164

21 TX (Indianola) 1886 4 150

22 MS/AL/Pensacola 1906 2 134

23 FL, GA, SC 1896 3 130

24 AGNES (FL/NE U.S.) 1972 1 122 f

25 HAZEL (SC/NC) 1954 4 95

Notes:

a Could be as high as 12,000

b Could be as high as 3000

c Total including offshore losses near 2000

d August

e Total including offshore losses is 600

f No more than

Records of the 2005 Atlantic Hurricane Season (Source: NOAA)

Most Numerous:

* 27 named storms (previous record: 21 in 1933) * 14 hurricanes (previous record: 12 in 1969)* Four major hurricanes hitting the U.S. (previous record: three in 2004) * Three Category 5 hurricanes (previous record: two in 1960 and 1961) * Seven tropical storms before August 1 (previous record: five in 1997) * Two-year consecutive total of tropical storms: 42 (previous record: 32 most recently in 1995-96) * Two-year consecutive total of hurricanes: 25 (previous record: 21 in 1886-87) * Two-year consecutive total of major hurricanes: 13 (ties record in 1950-51) * Two-year consecutive major hurricane landfalls: Seven (previous record: five in 1954-55) * Two -year consecutive Florida major hurricane landfalls: Five (previous record: three in 1949-50) * Three-year consecutive total of tropical storms: 58 (previous record: 43 most recently in 2002-04) * Three-year consecutive total of hurricanes: 31 (previous record: 27 in 1886-88) * Three-year consecutive total of major hurricanes: 16 (ties record in 1949-51 and 1950-52)

Costliest:

*Hurricane: Katrina (at least $80 billion) - (previous record Andrew, $26.5 billion - 1992 dollars)

Deadliest:

*U.S. hurricane since 1928: Katrina (at least 1,300)

Strongest:

* Hurricane in the Atlantic Basin: Wilma 882 millibars (mb) - (previous record: Gilbert at 888 mb)* Three of the six strongest hurricanes on record: Wilma 882 mb (1st), Rita 897 mb (4th), Katrina 902 mb (6th)* July hurricane: Emily (155 mph top sustained winds) - (previous record: Dennis (150 mph) in 2005;

Hurricane #1 (140 mph) in 1926

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25

30

35

40

-95 -90 -85 -80 -75 -70

Hurricane Katrina23-31 August

Hurricane

Tropical Storm

Tropical Dep.

Extratropical

Subtr. Storm

Subtr. Dep.

00 UTC Pos/Date

12 UTC Position

Low / Wave

PPP Min. press (mb)

25

24

31

30

29

2827

26

902 mb

920 mb

984 mb

928 mb

Track positions for Hurricane Katrina, 23-30 August 2005.

GOES-12 visible image of Hurricane Katrina over the central Gulf of Mexico at 1745 UTC 28 August 2005, near the time of its peak intensity of 150 kt.

Hurricane Wilma Rapid Intensification Over 72 hours

10/19/05 10/20/05

10/17/05 10/18/05

880

890

900

910

920

930

940

950

960

970

980

990

1000

1010

1020

10/15 10/17 10/19 10/21 10/23 10/25 10/27

Hurricane WilmaOctober 2005

BEST TRACK

Sat (TAFB)

Sat (SAB)

Sat (AFWA)

Obj T-Num

AC (sfc)

Surface

Pre

ssu

re (

mb

)

Date (Month/Day)

Selected pressure observations and best track minimum central pressure curve for Hurricane Wilma, 15-25 October 2005. Estimates during the extratropical stage are based partially on analyses from the NOAA Ocean Prediction Center. Vertical lines denote landfalls.