Validating Ship Reports during Hurricane Katrina

S. A. Hsu
Coastal Studies Institute
sahsu@lsu.edu

Abstract

Wind speeds as measured by the ships during Hurricane Katrina are compared to those based on the operational cyclostrophic equation using atmospheric pressure measurements. It is shown that, on the average, they are in good agreement for operational applications.

1. Introduction

A decade ago in August 2005 Hurricane Katrina (see Figures 1 and 2) devastated north-central Gulf of Mexico and southeastern Louisiana and Mississippi Gulf Coast (see, e.g., Wang and Oey, 2008).

The timeline of Katrina is provided in Table 1 and ship reports are in Table 2. The purpose of this study is to evaluate these ship reports.

2. Relation between Minimum Sea-level Pressure and Wind Speed at 10m

On the basis of the balance between centrifugal force and pressure gradient force Hsu (2005) has formulated an operational cyclostrophic equation such that:

U10 (in m/s) = 6.3 (1013 - Pmin) ^ (1/2) (1)

U10 (in knots) = 12 (1013 – Pmin) ^ (1/2) (2)

Where U10 is the wind speed at 10m and Pmin is the minimum sea-level pressure (hPa or mb).

Further validations of Equation (1) are presented in Figure 3 based on estimations from the National Hurricane Center (NHC) as listed in Table 1 during Katrina. Because nearly all anemometers on NDBC buoys were damaged, we employ the buoy measurement during Hurricane Lili in 2002 at NDBC Buoy 42001. Figure 4 illustrates that Equation (1) is in good agreement with the measurements made at 42001 (for location, see Figure 2) in 2002 over the Gulf of Mexico during Hurricane Lili. These results indicate that Equation (1) is very useful operationally.

3. Validating the Ship Reports

Now, if we substitute the pressure measurements from ship reports as listed in the 5th column in Table 2 into Equation (2), we get the estimated wind speed at 10m. Our results are shown in thelast column in Table 2. Since the difference between the averaged value of all ship reports (=41kts) and that of our computed averaged (=44 kts) based on the cyclostrophic equation is only 3 kts, we can say that these ship reports are consistent on the average with our theoretical reasoning. Furthermore, since the coefficient of variability of ship reports is 15% vs. that of 19% based on the cyclostrophic equation, these ship reports are validated to be reasonable.

4. Conclusions

On the basis of aforementioned evaluations and because of the composite effects of airflow distortion on and the height variation in the anemometer on ships, it is concluded that, on the average, these ship reports are reasonable and indispensable for operational applications such as the incorporation of these data onto the surface weather maps.

Katrina

Figure1. Image of Katrina over the central Gulf of Mexico near its peak wind conditions (see Table 1)

Linear relationship between visibility and air pressure

Figure 2. Hurricane Katrina's Track and NDBC Stations. Katrina's track (in red with the start of each day numbered) from the positions of the National Hurricane Center's Forecasts / Advisories (http://www.ndbc.noaa.gov/hurricanes/2005/katrina/)

figure3

Fig.3. Figure 3. A verification of Equation (1) based on data as listed in Table 1

figure4

Figure 4. Further verification of Equation (1) using the Hurricane Lili measurements made at Buoy 42001 during Lili in 2002

Damaged Vessels along the Mississippi coast following Katrina
Images coutesy NOAA Photo Library

Damaged Vessels along the Mississippi coast following Katrina Images coutesy NOAA Photo Library

Damaged Vessels along the Mississippi coast following Katrina
Images coutesy NOAA Photo Library

Damaged Vessels along the Mississippi coast following Katrina Images coutesy NOAA Photo Library




Table 1 (below). Timeline and characteristics of Hurricane Katrina over the Gulf of Mexico in August 2005

Advisory Number

Latitude Degrees

Longitude Degrees

Time UTC

Wind Speed, kts

Minimum sea-level pressure

Saffir/Smpson Category

11

25.3

-81.5

08/26/09Z

65

987

HURRICANE-1

11A

25.3

-81.8

08/26/11Z

65

987

HURRICANE-1

11B

25.2

-82

08/26/13Z

65

987

HURRICANE-1

12

25.1

-82.2

08/26/15Z

70

981

HURRICANE-1

13

25.1

-82.2

08/26/15Z

85

971

HURRICANE-2

13A

24.9

-82.6

08/26/18Z

85

969

HURRICANE-2

14

24.8

-82.9

08/26/21Z

85

965

HURRICANE-2

14A

24.7

-83.3

08/27/00Z

85

965

HURRICANE-2

15

24.6

-83.6

08/27/03Z

90

965

HURRICANE-2

15A

24.4

-84

08/27/06Z

95

963

HURRICANE-2

16

24.4

-84.4

08/27/09Z

100

945

HURRICANE-3

16A

24.4

-84.6

08/27/12Z

100

940

HURRICANE-3

17

24.5

-85

08/27/15Z

100

940

HURRICANE-3

17A

24.5

-85.4

08/27/18Z

100

949

HURRICANE-3

18

24.6

-85.6

08/27/21Z

100

945

HURRICANE-3

18A

24.8

-85.9

08/28/00Z

100

944

HURRICANE-3

19

25

-86.2

08/28/03Z

100

939

HURRICANE-3

20

25.1

-86.8

08/28/06Z

125

935

HURRICANE-4

21

25.4

-87.4

08/28/09Z

125

935

HURRICANE-4

22

25.7

-87.7

08/28/12Z

140

908

HURRICANE-5

23

26

-88.1

08/28/15Z

150

907

HURRICANE-5

23A

26.5

-88.6

08/28/18Z

150

906

HURRICANE-5

24

26.9

-89

08/28/21Z

145

902

HURRICANE-5

24A

27.2

-89.1

08/29/00Z

140

904

HURRICANE-5

25

27.6

-89.4

08/29/03Z

140

904

HURRICANE-5

25A

27.9

-89.5

08/29/03Z

140

908

HURRICANE-5

25B

28.2

-89.6

08/29/07Z

135

910

HURRICANE-5

26

28.8

-89.6

08/29/09Z

130

915

HURRICANE-5

26A

29.1

-89.6

08/29/11Z

125

918

HURRICANE-5

26B

29.7

-89.6

08/29/13Z

115

923

HURRICANE-4




Table 2 (below). Ship reports during Katrina

Date/Time UTC

Ship Call Sign

Latitude (0N)

Longitude (0W)

Pressure (mb)

Wind Speed

Cyclostrophic Equation U10 = 12(1013-P)^0.5, kts

25/1800

ZCAM5

26.8

79.3

1005.5

37

33

26/0600

WNDG

24.5

80.3

1005

45

34

26/0600

WTER

24.6

81.8

999.3

40

44

26/0600

KSYP

24.8

80.4

1004.5

36

35

26/1200

WFJN

24

81.8

1003

37

38

26/1400

WTER

24.6

81.8

1000.8

50

42

26/1500

WTER

24.6

81.8

1000.8

55

42

26/1800

WTER

24.6

81.8

1002.9

39

38

26/1900

WTER

24.6

81.8

1002.2

52

39

26/2100

C6FM9

24.4

80.4

1007

40

29

26/2100

WTER

24.6

81.8

1001.4

35

41

27/0000

ELQQ4

24.1

82

1000.5

37

42

27/0600

V7DW6

22.8

84.3

999

45

45

27/1200

KS049

22.7

84.5

994.1

36

52

27/1800

H3VR

23.2

83.3

1001

40

42

27/1800

KS049

23.5

82.6

994.5

41

52

27/1800

ELQQ4

25.5

83.1

1003.5

37

37

27/2100

WDB325

23.8

86.8

995.2

38

51

27/2100

WGXO

23.8

82.8

1001.2

37

41

28/0000

PFSK

21.1

84.4

1005.5

35

33

28/0000

WGXO

23.5

83.2

1000.3

37

43

28/0300

WGXO

23.2

83.8

1002

37

40

28/0300

WDB325

23.7

85.5

996

37

49

28/0000

WGXO

23

84.5

1001.2

44

41

28/0600

WDB325

23.7

84.7

999.5

54

44

28/0800

V7HD3

27.6

92.1

994

35

52

28/0900

WDB325

23.7

84

1001.2

48

41

28/1200

WGXO

23

85.9

999.5

44

44

28/1200

PFSK

23

85.7

1001.9

37

40

28/1200

PJOJ

27.6

83

1007.3

35

29

28/1400

AUBK

24

88.3

1000

37

43

28/1500

WGXO

23

86.8

1000.8

40

42

28/1500

C6FE5

23.1

86.5

1006.5

36

31

28/1500

V7HD2

27.1

91.6

1003

40

38

28/1800

C6FE5

23.8

87

1004.5

36

35

28/1800

MCLQ4

26

84.9

1005

42

34

28/1800

V7HC8

27.5

90.6

998

40

46

28/2100

WGXO

23.5

88.2

998.5

37

46

28/2100

V7HC6

26.2

91.4

993

35

54

28/2100

V7EA2

26.9

91.7

989.4

37

58

28/2100

V7HD2

27

92.3

1001

35

42

28/2100

V7HC8

27.4

90.9

997

35

48

29/0000

WGXO

23.7

89.1

998.8

37

45

29/0000

C6KJ5

24.9

89.4

994.5

38

52

29/0000

V7HC6

26.2

91.4

993.1

40

54

29/0000

ELXL3

26.6

90.9

990

55

58

29/0000

V7EA2

26.8

91.7

986.8

44

61

29/0000

V7HD2

27

92.7

1001

40

42

29/0000

V7HC9

27.1

92.6

998.6

37

46

29/0200

VRZN8

26.5

92.7

997

54

48

29/0300

C6KJ5

25.2

89.7

995.7

38

50

29/0300

ELXL3

26.5

90.8

991

52

56

29/0300

V7EA2

26.8

91.7

988.2

44

60

29/0400

V7HC8

27.1

91.4

996

40

49

29/0500

VRZN8

26.4

92.2

996

54

49

29/0600

C6KJ5

25.5

90

997

38

48

29/0600

ELXL3

26.4

90.8

994

45

52

29/0600

V7HC9

27

92.7

998.3

37

46

29/0600

MCLQ4

27.6

85.2

1005.6

36

33

29/0700

V7EA2

26.8

91.7

988

40

60

29/0800

V7HC9

27

92.7

998.6

38

46

29/0900

C6KJ5

25.9

90.5

997.5

35

47

29/0900

VRZN8

26.3

91.4

995

54

51

29/0900

ELXL3

26.4

90.8

996

44

49

29/0900

V7EA2

26.8

91.7

989

35

59

29/1100

C6FM8

22.3

88

1009

35

24

29/1200

VRZN8

26.5

91

995

47

51

29/1200

MCLQ4

28.3

85.5

1004.3

36

35

29/1500

VRZN8

26.9

90.7

999

54

45

29/1800

MCLQ4

28.3

86.4

1004.8

39

34

Mean:

41

44

Standard deviation:

6

8

Coefficient of variation:

15 percent

19 percent

References

Hsu, S. A., 2005. “Air-Sea Interaction”. In Water Encyclopedia, Vol. 4, pp. 1 - 4, Wiley - Interscience.

Wang, D.-P., and L.-Y. Oey, 2008, Hindcast of Waves and Currents in Hurricane Katrina, Bulletin of American Meteorological Society, 89 (4), 487-495.

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