Mariners Weather Log Vol. 59, No. 2, August 2015

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.

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/)

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

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

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.