Verification of the OCSI Atlantic Hurricane Predictions Since 1985

By:

Jill F. Hasling, CCM and Dr. John C. Freeman, CCM

Weather Research Center – Houston, Texas

www.wxresearch.com

  1. INTRODUCTION
  2. The Orbital Cyclone Strike Index [OCSI®] is based on the premise that the orbit of the Sun about the center of gravity of the solar system has an influence on the general circulation of the earth’s atmosphere. This influence is reflected in the paths of Atlantic tropical cyclones. Freeman and Hasling (2002) have recently pointed out that this orbit of the sun is shared by the earth. Jose (1969) and Landscheidt (1976) found that the orbit of the Sun is related to solar activity including the sun spot cycle. This seems to indicate that there are orbital influences reflected in the solar activity.

    Forecasts of the sections of the United States Coast with the highest risk of experiencing a landfall of a tropical storm or hurricane have been made since 1985. These forecasts have been verified and the results of this verification is given in the paper below.

    Secondary forecasts are made each year of the number of tropical cyclones expected each year as well as the number that would intensify into hurricanes. The number of storm days and hurricane days were also included in the outlook. The verification of these forecasts is also given with a comparison to Bill Gray’s seasonal outlooks.

  3. OCSI
  4. Recent research indicates that the premise that there could be orbital influences on the large scale circulation patterns in the earth’s atmosphere is plausible. Freeman and Hasling (2002) believe that the earth revolves around the center of the sun as the sun goes through its orbit about the center of gravity of the solar system. This orbit is believed to be one of the influences that drives the solar cycle [sun spot cycle] as well as cycles in the earth’s atmosphere.

    The OCSI starts with the years when the sunspot minimum occurs. These years are Phase 1 of the index. The year after the sunspot minimum would be Phase 2 and so on. A cycle could have as few as 9 phases or as many as 14 phases. This process creates the OCSI index in Table 1 which is made up of 10 cycles that start years 1878, 1889, 1901, 1913, 1923, 1933, 1944, 1954, 1964 and 1976.

    The Atlantic tropical cyclone data is then sorted into the index to determine which sections of the US coast has the most years with landfall of tropical storms or hurricanes in each Phase. Table 2 gives the probabilities for each section of the US coast by phase. The probability was computed by taking the number of years out of 10 that a storm made landfall on a particular section of the coast. This information is used to make a prediction of which section had the highest risk of experiencing a tropical cyclone landfall each year as well as which sections had the second highest risk each year.

     

     

    Forecasts have been made each year since 1985. The forecasts from 1985 which was phase 10 of Cycle 10 through 2003 were used for this verification. The cycle which started with 1851 and the cycle which started with 1867 were also used for verification.

    Figure 1 gives the forecast for each section of the United States Coast for Phase 9 [which will be the outlook for the 2004 Atlantic Hurricane Season]. As you can see from Table 1 the years which make up Phase 9 are 1886, 1897, 1909, 1921, 1931, 1941, 1952, 1962, 1972, and 1984. Figure 1 indicates how the highest and second highest probability was computed. Figure 1 indicates that the West Coast of Florida had 7 out of the 10 years [1886, 1897, 1909,1921,1931, 1941, 1952, 1962, 1972, 1984] which experienced landfall storms along the west coast of Florida. This gives the West Coast of Florida a 7 out of 10 chance or 70% chance of experiencing a tropical storm or hurricane. For Texas there 6 out of the ten years when a tropical storm or hurricane made landfall on the Texas coast.

    The years that had Texas landfalls were 1886, 1897, 1909, 1921, 1931 and 1941. This gives Texas the second highest probability in the 2004 season out look or a 60% chance.

    When reviewing the years in each phase some the significant events are noted. For example in Phase 9 of the OCSI, there have been several very significant hurricanes. There was the 1875 Texas hurricane which almost destroyed the town of Indianola and in 1886 another hurricane did destroy the town of Indianola. Other strong Texas storms during this Phase of the OCSI were in 1909, 1941. There was a very strong Florida Keys hurricane in 1909 as well as a very strong Louisiana hurricane in 1909.

     

  5. VERIFICATION OF THE OCSI
  6. The verification of the forecast made each year from 1985 to 2003 is in Table 3. A forecast verifies with landfall in at least one the sections with the highest probability of landfall. In the past 19 years there have been only 2 years [1987 and 1992] when a storm did not make landfall in any of the sections with the highest probability. This gives you an accuracy of 89.5%.

    Hindcasts were made for 1851 10 1877. These hindcasts were verified and the results appear in Table 4. There were 22 years that hindcasts were made. Out of those 22 years there were 5 years when a cyclone did not make landfall in the section of the coast with the highest risk, for an accuracy rate of 77%. Summaries of Table 3and 4are given below.

    Years Highest Forecasts

    1856

    11 years

    4 years missed

    64%

    1867

    11 years

    1 year missed

    91%

    1986

    10 years

    2 years missed

    80%

    1996

    8 years

    1 years missed

    87.5%

    An alternate verification process would be to consider that 30 forecasts of the highest probable section of the US coast could be made in the 19 years. There were 9 times when a storm did not make landfall for one of these forecasts. In other words, there were 9 missed forecasts out of the 30 forecasts with an accuracy rate of 70%. For the hindcasts made from 1856 to 1877, there were 34 hindcasts made in the 22 years of the sections of the United States coast with the highest risk of a tropical cyclone making landfall. There were 7 missed hindcasts for an accuracy rate of 79%.

     

     

     

    Total Highest Forecasts

    1856

    17 forecasts

    5 missed

    71%

    1867

    17 forecasts

    2 missed

    88%

    1986

    16 forecast

    7 missed

    56%

    1996

    13 forecasts

    1 missed

    92%

     

    Looking at Table 2, climatology would have forecast each year that the West Coast of Florida had the highest chance each year of experiencing a landfall from a tropical storm or hurricane. Based on climatology there is a 71 percent chance of a storm on that section of the coast line. Out of the 40 years there were 10 years when storms did not make landfall on the west coast of Florida for an accuracy rate of 75%.

     

    Highest Climatology Forecasts

    1856

    11 years

    5 years missed

    55%

    1867

    11 years

    1 year missed

    91%

    1986

    10 years

    4 years missed

    60%

    1996

    8 years

    0 years missed

    100%

    There have been 40 years that forecasts or hindcasts were made. Of those 40 years, there were only 7 years when a tropical storm or hurricane did not make landfall in one of the sections with the highest risk. This gives you an accuracy rate of 83%. There have been 62 forecast made in the 40 years with the highest risk and there have only been 14 times in the 40 years when a tropical storm or hurricane did not make landfall in one of 62 forecast areas. This gives you an accuracy rate of 77%.

  7. WRC’s FORECAST COMPARED TO GRAY’s FORECAST

In order to compare the OCSI with other Atlantic Seasonal hurricane outlooks, secondary predictions where made of the number of tropical cyclones, number hurricanes, number of tropical storm days, and number of hurricane days each year. These forecasts were compared to climatology as well as the forecast made by Colorado State Professor Bill Gray. The years used for this comparison were for the twenty years from 1984 to 2003.

The secondary predictions were made by averaging the number of storms for the years in each phase as well as average the number of tropical storm days and hurricane days. These numbers were used to make the secondary outlook each year.

This verification of the twenty years of forecast demonstrates that WRC’s OCSI model is as accurate if not more accurate than Gray’s model. The advantage of the OCSI model is that WRC’s model can make a prediction years in advance. Table 5 gives a summary of the forecasts comparisons that are shown in Table 6 through 9. This table gives the number of years that each model was closest within the limits indicated.

WRC forecast the number of storms each year and this forecast was verified for the past 20 years. There were eight years out of the twenty years when WRC’s forecast was within plus or minus one storm. Gray’s forecast was only within one storm five of the twenty years and climatology was only within one storm two of the twenty years. This is shown in Table 6. Figure 2 shows a graph comparing the plus or minus error in the forecast versus observed. This graph also shows the forecast error for the forecast made by climatology.

The graph seems to indicate that climatology and WRC’s method has under forecast the number of storms in the Atlantic since 2001. In 1997 WRC forecast the correct number of storms. Other years when WRC forecast the exact number of storms were 1994, 1992, and 1987

WRC forecast the number of hurricanes each year. The forecast verified within one hurricane ten out of the twenty years and Gray’s method forecast within one hurricane eight of the twenty years. WRC forecast the number of hurricane days each year. This verified within five days eight out of the twenty years. Table 7 shows the comparison of the forecast erros.

Gray’s method forecast the number of hurricane days within five days six out of the twenty years and climatology was five out of the twenty years. WRC’s model then forecast the number of storm days, this verified within ten days for ten of the twenty years. Gray’s model forecast the number of days within ten days for seven of the twenty years and climatology five out of the twenty years. Table 8 gives the detail of these comparisons.

Table 9 gives the forecast for both WRC’s and Gray’s model for the number of storm days in each year. WRC’s model forecast the number of days within ten days for ten of the twenty years. Gray’s model forecast the number of days within ten days for seven of the twenty years.

This verification of the twenty years of forecast demonstrates that the WRC’ OCSI model is as accurate if not more accurate than Gray’s model. The advantage of the OCSI model is that WRC’s model can make a prediction years in advance. .

REFERENCES:

Gray, William M., Philip J. Klotzbach, and Chrisopher W. Landsea, 2003, Updated Forecast of Atlantic Seasonal Hurricane Activity and US Landfall Strike Probability for 2003, Dept. of Atmopsheric Science, Colorado State University/

Gray, William M, Christopher W. Landsea, Paul W. Mielke, Jr., Kenneth J. Berry, and Erick Blake, 2000; Summary of 2000 Atlantic Tropical Cyclone Activity and Verification of Aurthor’s Seasonal Activity Forecasts – Appendix A: Verification of Past Seasonal Forecasts, Colorado State University.

Freeman, John C. and Jill F. Hasling, 2003, The Effect of the Orbit of the Sun on the Earth’s Atmosphere, AMS Annual Meeting

Jose, P.D., 1965, Sun’s Motion and Sunspots, Astronomical Journal 10,(1),193-200.

 

 

Table 1: Orbital Cyclone Strike Index

Phase

1

1878

1889

1901

1913

1923

1933

1944

1954

1964

1976

2

1879

1890

1902

1914

1924

1934

1945

1955

1965

1977

3

1880

1891

1903

1915

1925

1935

1946

1956

1966

1978

4

1881

1892

1904

1916

1926

1936

1947

1957

1967

1979

5

1882

1893

1905

1917

1927

1937

1948

1958

1968

1980

6

1883

1894

1906

1918

1928

1938

1949

1959

1969

1981

7

1884

1895

1907

1919

1929

1939

1950

1960

1970

1982

8

1885

1896

1908

1920

1930

1940

1951

1961

1971

1983

9

1886

1897

1909

1921

1931

1941

1952

1962

1972

1984

10

1887

1898

1910

1922

1932

1942

1953

1963

1973

1985

11

1888

1899

1911

1943

1974

12

1900

1912

1975

 

 

 

Table 2: OCSI FORECASTS

Phase

Mexico

Texas

Louisiana – Alabama

West Florida

East Florida

Georgia-N. Carolina

East US Coast

GOM Oil Block

1

40

40

60

70

50

90

60

90

2

40

40

70

60

40

60

40

80

3

70

60

40

90

70

20

20

80

4

40

70

90

90

60

70

40

100

5

20

30

60

60

30

60

20

90

6

40

40

70

70

30

60

50

70

7

20

60

60

80

40

30

10

90

8

30

40

50

50

30

70

70

80

9

50

60

40

70

30

40

30

70

10

50

70

50

70

30

60

20

100

>10

25

50

75

63

13

50

25

88

Avg

40

51

59

71

41

56

36

85

 

 

 

 

Figure 1: Past Storms in Phase 9 by Section of US Coast

The sections with the highest number of storms in past years were West Florida Coast with storms in 8 of the 11 years and Texas with storms in 7 of the 11 years

 

 

 

 

 

 

Table 3: OSCI Verification

Year

Highest

1

1985

TX 70% W FL 70%

Kate

2

1986

GA/NC 90%

Charley

3

1987

LA/AL - 70%

X

4

1988

W. FL 90%

Keith

5

1989

LA-AL 90% WFL 90%

Allison

6

1990

W FL 60% GA-NC 60% LA-AL 60%

Marco

7

1991

W FL 70% LA-AL 70%

Fabian

8

1992

W FL 80%

9

1993

NE US 70% GA-NC 70%

Emily

10

1994

W FL 70%

Alberto Beryl Gordon

11

1995

TX 70% W FL 70%

Dean Allison Erin Opal

12

1996

GA-NC 90%

Arthur – Bertha – Fran

13

1997

LA-AL 70%

Danny

14

1998

W FL (90%)

Earl Mitch

15

1999

LA-AL 90% WFL90%

Harvey Irene

16

2000

W FL 60% LA-AL 60% GA-NC 60%

Gordon/Helene Gordon Helene

17

2001

W FL 70% LA-AL 70%

Gabrielle Allison

18

2002

W FL 80%

Hanna

19

2003

NE US 70% GA-NC 70%

Isabel Isabel

 

 

 

 

 

 

Table 4: OSCI Verification 1856-1877

Year

Highest

1

1856

GA/NC 90%

Strm#3

2

1857

LA/AL - 70%

3

1858

W. FL 90%

Strm#3

4

1859

LA-AL 90% WFL 90%

Strm#5 Strm#5

5

1860

W FL 60% GA-NC 60% LA-AL 60%

Strm#1 Strm#1/4/6

6

1861

W FL 70% LA-AL 70%

Strm#6 Strm#2

7

1862

W FL 80%

8

1863

NE US 70% GA-NC 70%

Strm#6 Strm#6

9

1864

W FL 70%

10

1865

TX 70% W FL 70%

Strm#2/4 Strm#7

>10

1866

LA-AL 75%

Year

Highest

1

1867

GA/NC 90%

Strm#1

2

1868

LA/AL - 70%

Strm#1

3

1869

W. FL 90%

4

1870

LA-AL 90% WFL 90%

Strm#1 Strm#6/9

5

1871

W FL 60% GA-NC 60% LA-AL 60%

Strm#6/7 Strm#3 Strm#7

6

1872

W FL 70% LA-AL 70%

Strm#5 Strm#1

7

1873

W FL 80%

Strm#3/4/5

8

1874

NE US 70% GA-NC 70%

Strm#6 Strm#6

9

1875

W FL 70%

Strm#3

10

1876

TX 70% W FL 70%

Strm#5

>10

1877

LA-AL 75%

Strm#14

 

 

Table 5. Summary of Model Comparison

# of Storms in Atlantic

within 1 storm

WRC OCSI

8 Years

CLIMATOLOGY

2 years

Gray’s Fcst

5 years

# hurricanes in Atlantic

within 1 storm

10 years

5 years

8 years

# of hurricane days

with 5 days

8 years

4 years

6 years

# of storm days

within 10 days

10 years

5 years

7 years

Table 6: Number of Named Storms in the Atlantic

Year

OBS

WRC FCST

WRC Error

Gray

APR FCST

GRAY APR Error

CLIMATE

Error

1984

12

7

-5

10

-2

-2

1985

11

10

-1

11

0

-1

1986

6

11

5

8

2

4

1987

7

7

0

8

1

3

1988

12

8

-4

11

-1

-2

1989

11

10

-1

7

-4

-1

1990

14

8

-6

11

-3

-4

1991

8

9

1

8

0

2

1992

6

6

0

8

2

4

1993

8

7

-1

11

3

2

1994

7

7

0

9

2

3

1995

19

10

-9

10

-9

-9

1996

13

11

-2

11

-2

-3

1997

7

7

0

11

4

3

1998

14

8

-6

10

-4

-4

1999

12

10

-2

14

2

-2

2000

14

8

-6

11

-3

-4

2001

15

9

-6

10

-5

-5

2002

12

6

-6

12

0

-2

2003

16

7

-9

12

-4

-6

 

 

 

 

Figure 2: Comparison of the Error on the number of forecast storm.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 7: Number of Hurricanes in the Atlantic Basin

Year

OBS

WRC FCST

WRC Error

Gray Apr/Jun

Gray Error

CLIMATE Error

1984

5

4

-1

7

2

1

1985

7

5

-2

8

1

-1

1986

4

5

1

4

0

2

1987

3

4

1

5

2

3

1988

5

5

0

7

2

1

1989

7

6

-1

4

-3

-1

1990

8

5

-3

7

-1

-2

1991

4

6

2

4

0

2

1992

4

3

-1

4

0

2

1993

4

5

1

7

3

2

1994

3

4

1

5

2

3

1995

11

5

-6

6

-5

-5

1996

9

5

-4

7

-2

-3

1997

3

4

1

7

4

3

1998

10

5

-5

6

-4

-4

1999

8

6

-2

9

1

-2

2000

8

5

-3

7

-1

-2

2001

9

6

-3

6

-3

-3

2002

4

3

-1

7

3

2

2003

7

5

-2

8

1

-1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 8: Number of Hurricane Days

Year

OBS

WRC FCST

WRC Error

Plus/Minus

Days

Gray Apr/Jun FCST

Gray Error

Plus/Minus

Days

Climate

Error

1984

18

16

-2

30

12

7

1985

21

21

0

35

14

4

1986

11

24

13

15

4

14

1987

5

7

2

20

15

20

1988

21

25

4

30

9

4

1989

32

30

-2

15

17

-7

1990

27

20

-7

30

3

-2

1991

8

20

12

15

7

17

1992

16

15

-1

15

0

9

1993

10

21

11

25

15

15

1994

7

16

9

15

8

18

1995

62

21

41

25

37

-37

1996

45

24

-21

25

-20

-20

1997

10

7

-3

25

15

15

1998

49

25

-24

20

-29

-24

1999

43

30

-13

40

-3

-18

2000

32

20

-12

25

-7

-7

2001

27

20

-7

25

-2

-2

2002

11

15

4

30

19

14

2003

32

21

-11

35

-3

-4

 

 

 

 

 

 

 

 

 

 

 

Table 9: Number of Storm Days in the Atlantic

Year

OBS

WRC FCST

WRC Error

Plus/Minus

Days

Gray Apr/Jun FCST

Gray Error Plus/Minus

Days

Climate

Error

1984

51

55

-4

45

6

-2

1985

51

68

-17

55

-4

-2

1986

23

83

-60

35

-12

26

1987

37

47

-10

40

-3

12

1988

47

57

-10

50

-3

2

1989

66

69

-3

30

36

-17

1990

66

58

8

55

11

-17

1991

22

64

-42

35

13

27

1992

39

41

-2

35

-4

10

1993

30

50

-20

55

25

19

1994

28

55

-27

35

7

21

1995

121

68

53

50

71

-72

1996

78

83

-5

55

23

-29

1997

28

47

-19

55

-27

21

1998

80

57

23

50

30

-31

1999

77

69

8

65

12

-28

2000

66

58

8

55

11

-17

2001

63

64

-1

50

13

-14

2002

54

41

13

65

-11

-5

2003

71

50

-21

65

6

-26