OCSI Atlantic Hurricane Predictions Versus Bill Gray’s Seasonal Forecasts

By:

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

Weather Research Center – Houston, Texas

http://www.wxresearch.com

 

WRC’s OCSI FORECASTs COMPARED TO GRAY’s FORECASTS

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.

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 1 gives a summary of the forecasts comparisons that are shown in Table 2 through 5. 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 2. Figure 1 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.

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 3 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 4 gives the detail of these comparisons.

Table 5 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. .

 

 

Table 1. 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 2: 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 1: Comparison of the Error on the number of forecast storm.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 3: 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 4: 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

-7

 

 

 

 

 

 

 

 

 

 

 

Table 5: 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

~75

50

25

65

10

-26