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Wave Hazard Assessment for Selected Sites on the West Coast of Dominica, West Indies

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Caribbean Disaster Mitigation Project

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2. History of Storms on Dominica: HURSTAT

The events most likely to generate significant waves for the study site are tropical cyclones. As of 1996, the US National Center for Atmospheric Research has 110 years of reliable, standardized weather data for the region. The HURSTAT program, developed by Charles Watson in conjunction with CDMP, extracted statistics for Dominica, using the latitude and longitude of a point near the center of the west side of the island.

The storms are sorted by category of intensity, according to the Saffir/ Simpson hurricane scale. HURSTAT gives the storm category according to the pressure and wind strength at the longitude and latitude chosen. Many of these historical storms had higher intensities at their centers, but the centers did not pass over the chosen location, and HURSTAT compensates for that.

Table 1. Saffir / Simpson Hurricane Scale (Adapted from Lutgens & Tarbuck)

Category Pressure

(millibars)

Winds

(km/hr)

Storm Surge

(meters)

Damage
0 Tropical storm > = 995 61 - 119 0.5 - 1.2 Some
1 Hurricane 980 - 995 119 - 153 1.2 - 1.5 Minimal
2 " 965 - 979 154 - 177 1.6 - 2.4 Moderate
3 " 945 - 964 178 - 209 2.5 - 3.6 Extensive
4 " 920 - 944 210 - 250 3.7 - 5.4 Extreme
5 " < 920 > 250 > 5.4 Catastrophic

 

Table 2. General Statistics for Dominica, at Lat 15.5, Lon 61.4, for 1886 to 1996

Number of storms 61
Years with storms 45
Years with multiple storms 13
Years with multiple hurricanes 1
Category 0, tropical storms 40
Category 1, hurricanes 13
Category 2 " 3
Category 3 " 3
Category 4 " 2
Category 5 " 0

 

Table 3. Interval Analysis for Tropical Storms or Greater at Lat 15.5, Lon 61.4, for 1886 to 1996

Intervals Found 35
Average Interval 2.885714 years
Maximum Interval 12 years
Minimum Interval 1 year
   
Interval between storms (years) Number of occurrences of interval
1 15
2 10
3 1
4 2
5 1
6 2
7 1
8 1
11 1
12 1

 

Table 4. Interval Analysis for Hurricanes of Category 1 or Greater at Lat 15.5, Lon 61.4, for 1886 to 1996

Intervals Found 17
Average Interval 5.764706 years
Maximum Interval 20 years
Minimum Interval 1 year
   
Interval between storms (years) Number of occurrences of interval
1 3
2 5
4 2
5 1
7 1
10 2
12 1
13 1
20 1

 

Table 5. Interval Analysis for Hurricanes of Category 2 or Greater at Lat 15.5, Lon 61.4, for 1886 to 1996

Intervals Found 7
Average Interval 13.57143 years
Maximum Interval 34 years
Minimum Interval 2 years
   
Interval between storms (years) Number of occurrences of interval
2 2
8 1
10 1
13 1
26 1
34 1

 

Table 6. Interval Analysis for Hurricanes of Category 3 or Greater at Lat 15.5, Lon 61.4, for 1886 to 1996

Intervals Found 4
Average Interval 23.75 years
Maximum Interval 70 years
Minimum Interval 2 years
   
Interval between storms (years) Number of occurrences of interval
2 1
10 1
13 1
70 1

 

Table 7. Interval Analysis for Hurricanes of Category 4 or Greater at Lat 15.5, Lon 61.4, for 1886 to 1996

Intervals Found 1
Average Interval 15 years
Maximum Interval 15 years
Minimum Interval 15 years
   
Interval between storms (years) Number of occurrences of interval
15 1
Warning: With only two C4 hurricanes, interval analysis is doubtful.

The numbers in the tables above need to be used with caution. For instance, Table 3 indicates that there would be an interval of nearly three years (2.88 years) between storms, on the average. But, looked at in another way, the Table 3 says that there are 15 chances out of 35 that any given interval will last only a year, and 25 chances out of 35 that it will last two years or less.

In order to relate these statistics to personal experience, it is useful to remember that Hurricane Marilyn of 1995 was a strong Category 1, and that Hurricane David of 1979 was a strong Category 4 hurricane.

Personal experience offers only limited help in assessing the risk of severe storms, however. Table 4 shows that there was one interval when Dominica did not have a hurricane for twenty years. People who grew up during that calm period may have felt complacent about hurricanes, based on their experience, but they were wrong to do so.

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