it is a sure sign of weather change. If the rate of fall is 1 to 2 millibars (0.03 to 0.06 inches of mercury) per hour, it can signal danger.
In June 1996, a group of sailboats set out from New Zealand to Tonga. It was an informal regatta that included all types of boats, from monohulls to catamarans. The atmospheric pressure was 1,020 millibars. Without warning, after the boats were under way, a tropical depression began forming between Vanuatu and Fiji. The atmospheric pressure dropped suddenly from 1,001 to 986 millibars and the next day to 979 millibars. When the atmospheric pressure in a tropical depression drops at the rate of 1 millibar per hour for 24 hours, the New Zealand Meteorological Service refers to it as a “meteorological bomb.” The gale from this depression moved southwest across the center of the fleet sailing for Tonga. Boats in the Force 12 storm’s path were brutalized by high winds and violent seas. Five boats were lost, a number of rescues were carried out, and miraculously only three persons drowned. New Zealand Air Force planes involved in rescue attempts reported surface winds at 70 to 80 knots and wave heights up to 100 feet. The boats at the center of the storm reported Force 12 conditions. Boats were knocked down, dismasted, rolled over—some several times. Crews frantically reported their condition and location by shortwave radio to Auckland. A freighter in the area, a French navy ship, and New Zealand naval and air force personnel all came to the rescue.18
The crew of one disabled vessel was rescued by a large cargo ship. As the captain skillfully maneuvered the huge vessel close to the small sailboat, the crew waited for the exact moment when the mountainous seas crested, leapt from the sailboat to cargo nets hanging from the side of the larger ship, and then climbed as fast as they could to avoid being swept away by a giant wave. The jump had to be perfect—there would be no second chance in those roiling waters. With each passing wave, the two vessels ground together with a horrific noise as the sailboat drifted toward the stern of the cargo ship. When all of the sailors were safely aboard, they watched in horror as their beloved boat passed under the stern of the cargo ship. As the larger ship slammed down into