Ivan’s path erratic

It would appear that everyone watching the travels of Hurricane Ivan were on the wrong path.

The United States National Hurricane Center’s report on Hurricane Ivan contains a section headed ‘Forecast and Warning Critique’ and notes that the National Hurricane Center’s official track forecast was at most times outperformed during Ivan by the UKMET and FSU Superensemble numerical track forecast models.

The official track forecasts, it notes, ‘had, in general, a persistent right-of-track bias for the first 11 days of Ivan’s existence as a tropical cyclone.’

This right-of-track bias of the official forecast had Ivan turning north farther east, or right, of the Cayman Islands because it relied on global models that showed a strong subtropical ridge north of Ivan eroding more quickly than it ultimately did.

Although some residents of the Cayman Island have spoken of Ivan ‘bouncing off the mountains of Jamaica,’ the report gives another possible explanation: ‘The westward jog that Ivan made on 11 September appears to be, at least in part, the result of a mid-to-upper-level cold low to the north of Hispaniola that moved slowly southwestward rather than weakening and lifting out to the northeast as some of the models had been forecasting.’

Director of Meteorological Services Fred Sambula said in a recent interview that it is not possible to predict a hurricane’s path with any certainty. ‘It’s going to be an on-going argument as to which model does better,’ he said. ‘One of the flaws in computer models is that they tend to base their conclusions on the assumption that all hurricanes will behave as others did.

‘We’ve tried to model the atmosphere, but there are so many variables that affect the time and space path of a hurricane. We try to take one element, temperature for example, and determine what effect it will have on a hurricane’s path, not really knowing how it will interact with some of the other elements,’ he said.

‘Instead of looking at one variable, maybe we should be looking at them all, but our computer models aren’t up to that capability yet,’ he concluded.

The difficulty in predicting a hurricane’s path underscores a common fallacy.

‘We look at the line of a hurricane’s predicted path and tend to focus on that point,’ Mr. Sambula said. ‘A hurricane is not a point. In truth, a hurricane is a wide area of destruction. If it was heading for Cayman Brac and was 400 miles across, of course we should have been concerned in Grand Cayman.’

Chief Meteorologist Jeff Tibbetts agrees, pointing out that predicted hurricane paths also show a wider margin of error area in which the hurricane could conceivably travel. ‘If you are anywhere within that error band, it means that we should start a high level of preparation,’ he said.

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