Landfalling Hurricanes

Storm-Oriented vs. Location-Oriented Forecast Information

Since the highest winds are closer to the eye of the storm and the lesser winds are farther out, it is important for people to know which part of the storm's wind field may be likely to intersect their location. This will depend on the storm's trajectory relative to the location, its intensity, and the size and structure of its wind field as it moves through the area.

Some classes of hurricane forecast information with landfall implications exhibit more of a storm-oriented perspective, while others lend themselves to a more location-oriented perspective. A storm-oriented perspective wants to know where the storm's next position is likely to be at some fixed time in the future, and where, if anywhere, on its track the center of a hurricane might intersect land. A location-oriented perspective is concerned with what is likely to happen at a particular place near the coastline, specifically, what kinds of conditions, if any, the residents or industries based there are likely to experience as a result of the landfalling hurricane.

The storm-oriented perspective begins in the water and follows the progression of the center or eye of the storm onto land. It is satisfied by the latitude/longitude coordinates contained in the track forecast and the cone of uncertainty, together with the maximum sustained winds contained in the intensity forecast. The first latitude/longitude pair that describes a location on land instead of in water indicates that landfall of the center is expected seaward of that location. The actual forecast coordinates would be located slightly inland from the predicted landfall area, unless the landfall projection happened to coincide exactly with one of the standard forecast times (that is, if landfall were forecasted to occur exactly 12, 24, 36, 48, 72, etc. hours after the initial time).

Except in that rare instance, the track forecast, a storm-oriented product, does not contain an explicit landfall forecast (a direct statement about projected landfall coordinates). The appearance of a land mass anywhere within the cone of uncertainty contains the same implicit landfall forecast information as the track forecast coordinates but with two-thirds of the statistical uncertanty taken into account. The projected intensity at landfall is also not explicitly stated but can be inferred from whatever category forecast was in effect at the last forecast time the storm was still predicted to be over water, and from the projected intensity trend immediately thereafter.

The location-oriented perspective, in contrast, begins and ends on land; it has to take into consideration the landfall not only of the center but of any part of the storm's wind field, which can radiate tens of miles out from center (hurricane-force winds) or hundreds of miles outward (tropical storm-force winds). It also has to take into account that those hurricane-force winds could be anywhere from Category-1 intensity (74 mph or greater) all the way up to Category-5 (155 mph or greater), depending on which part of the wind field passes over the location. A smaller, tightly-wound storm will by definition have wind fields of lesser extent and reach, and thereby a lesser chance of intersection of the worst parts of it with a built-up area. One of the many reasons Hurricane Katrina was so devastating was that it affected such a vast region, due in part to the large size of its most damaging wind fields.

Watches and warnings, together with wind speed probabilities - which contain statements about the likely potential of different parts of the tropical cyclone's wind field to intersect specific locations both on land and in water - contain more location-oriented predictive information than the track, intensity, and size forecasts taken alone.

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