As predicted, the Atlantic hurricane season of 2010 has been stormy. To date, there have already been six hurricanes, and four of these — Danielle, Earl, Igor and Julia — reached massive category 4 status for a time (top sustained winds between 135 and 150 miles per hour). Fortunately, these powerhouse hurricanes have not impacted the mainland United States in any major way. Earl made a swipe at the East Coast in early September, but the strongest winds were well offshore, to the east of the center. The offshore oil rigs in the Gulf of Mexico have been spared any significant impact as well.
However, conditions are brewing in the Caribbean Sea that may signal the approach of a hurricane somewhere in the southeastern United States around the end of this month. Additionally, Tropical Storm Matthew is moving into Central America tonight. This storm will likely weaken over Central America this weekend and die.
A full-blown La Nina has blossomed in the Pacific Ocean. La Nina’s cooler waters have muffled the strong high altitude winds over the Atlantic that made last season, when there were only three hurricanes, so quiet. The Atlantic Ocean continues to be warmer than usual, creating more fuel. A steady train of tropical weather disturbances continues to migrate off the coast of Africa and plow westward. As they steadily traverse the Atlantic, they feed on the warm, humid air over the bathtub-like temperatures of the tropical Atlantic Ocean and grow stronger.
Hurricanes may have awesome power, but they have no control over their own destiny. A hurricane is imbedded in the ocean of air that is our atmosphere. It is this ocean of air that sweeps the hurricane along in its ever-changing current that eventually determines where and when a hurricane will or will not strike. The wind currents of the atmosphere are impossible to measure perfectly, even with today’s equipment — there are always going to be errors in our readings about how the ocean of air is behaving. Small errors in our initial measurements of the atmosphere can contribute to large errors in forecasts many days into the future.
Computer models are used to simulate the atmosphere’s behavior. These mathematical weather simulators have limitations. Although brilliant creations, they do not incorporate all of the subtleties that make the atmosphere work. In addition, the model predictions are highly dependent on how well we measure the initial state of the atmosphere. If we don’t measure all the significant atmospheric disturbances to start with, the models are immediately handicapped and will make inaccurate predictions. As a result, the models sometimes predict storms that never happen. Large and dangerous hurricanes have been generated by the models as much as 10 to 15 days into the future that turn out to be “computer dreams.”
One element we look for in the models is the persistence of a prediction. If a model predicts a storm over and over again from one forecast to the next, the possibility of it actually happening grows. If a hurricane is being forecast from the same model over a number of consecutive days, this is significant. It indicates there must be a disturbance in the atmosphere that is repeatedly being captured by our measurement, and is significant enough that the model can predict its future evolution. This persistence of prediction is enough to indicate a degree of credibility.