Hurricane Danielle reached category 4 status this past Friday and was all set to send solid swell throughout the East Coast. Buoys along Florida and the Southeast were up, but wave heights along the Northeast left some in the upper half of the coast wondering where this mystical swell went?
So, how far of an overcall was it?
Well, some buoys along the Northeast were as little as 50 percent of the swell heights forecasted by Swellinfo as well other forecasting sources. This is not to say there was not good surf to be found along the Northeast, but most areas in the Northeast were generally smaller than anticipated. We have received feedback of very good surf in some areas, but this seem to peak around head high or so and in very localized areas.
It is important to note that with long period swells, there will always be more variability for individual breaks, since the long period swells are much more influenced by the ocean bottom. This allows for more refraction to focus swell energy towards some areas and away from others.
So, why such an overcall?
Well, to be honest, it is a bit unclear why the forecast models, which we are very reliant upon, over called the swell in the Northeast. As we mentioned above, forecasts were on target for the lower half of the East Coast. The best guess we have at Swellinfo of the overcall, is due to Danielle's quick shift to the Northeast. As a hurricane moves away from the coast, very little if any swell will be produced in the opposite direction of the storms movement. This is well understood, but what we think could be the source of error, which has been visible in the past is the following: As the storm changes direction away from the coast, it can act almost like a vacuum, where the strong winds on the west side of Danielle impede on the existing SE swell propagation. There are several other possibilities for error, but this is our strongest assumption at this point, where the wave model is not able to calculate this phenomenon.
So, how are we going to forecast better in the future?
Swellinfo has been experimenting with buoy data validation techniques for a while. Due to the nature of the Danielle swell, we have decided to release the forecast upgrade as of this evening (Sunday august 29th, 2010). It is currently being applied to the US East Coast and will be expanded to cover all forecast areas in the near future.
We hear you!
We are very happy with our proactive Swellinfo community section, and we always listen to when our users have positive or negative feedback. And, yes, we did hear the disappointed comments left by users in the Northeast. We are always striving to improve upon Swellinfo, and that is why we went into quick action to release the new forecast upgrade.
Don't look now, here comes Hurricane Earl!