Construct the requested confidence interval. A meteorologist was interested in the average speed of a thunderstorm in his area. He sampled 13 thunderstorms and found that the average speed at which they traveled across the area was 15 miles per hour with a sample standard deviation of 1.7 miles per hour. Assuming the speed of a thunderstorm is approximately normal, construct a 99% confidence interval for the true average speed of a thunderstorm in his area.