WRAL WeatherCenter Blog

Longer Leads from the Hurricane Center

Posted January 9, 2010

Forecast "fan" and advisories associated with Hurricane Ida. Watches and warnings for storms like these may be issued between 12 and 24 hours earlier under new policies being implemented for 2010 by the National Hurricane Center.

You've probably heard news reports about the improvements through the years in hurricane track forecasting, a result of better data collection, research on factors that influence the patch taken by the storms, more powerful computers and the resulting upgrades in computer models that project these tracks. One outcome of all this is that the average error of track forecasts from the National Hurricane Center have been cut in half over the past 15 years or so. Unfortunately, forecasting the intensity changes that will occur with the storms remains a greater challenge, and relatively little improvement has been made there. Still, having greater confidence where the storm will be and when is a major achievement.

Just a few years back, this led NHC to increase the time span covered by their official forecasts from three days to five days into the future. Now, they are taking the next step and increasing the lead time they will apply to their tropical watches and warnings. This will bring a change to the definitions of those advisories, one that is intended to allow preparedness activities and, as needed, evacuations, to get underway at an earlier point in the approach of a storm.

I've included a link to the NHC web site where they summarize the reasons behind the change, and where they provide the new definition for each watch and warning product. The bottom line is that there are two meaningful changes. One, they will increase the lead time on these products by twelve hours, and, in a more subtle change, those lead times will be applied to the expected onset of tropical storm force winds, for both tropical storm and hurricane watches and warnings. Taken together, this could mean watches and warnings for some large storms that are issued at least 12, and as many as 18-24 hours earlier than in the past.

There are probably some trade-offs involved in this policy. By extending the lead times this much, "false alarms" may increase a bit relative to recent years, but due to the increase track accuracy shouldn't be higher than they were a decade or so ago. On the other hand, the earlier timing should be a boon for emergency management agencies that have to enact preparedness and evacuation plans, and will hopefully result in meaningful savings of life and property.


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