Why Hurricane Arthur Is a Weather Forecaster's Worst Nightmare

Daniel Brown, Senior Hurricane Specialist at the National Hurricane Center, tracks Hurricane Arthur, the first of the 2014 Atlantic hurricane season on July 3, 2014 in Miami, Florida.

Hurricane Arthur is the type of storm hurricane forecasters dread — it is intensifying, gaining speed and tracking much closer to land than originally anticipated.
Rather than grazing the Outer Banks of North Carolina as a strong tropical storm or minimal Category 1 hurricane, it is likely to make landfall as a Category 2 — or possibly even Category 3 — storm, with maximum sustained winds of around 100 miles per hour. This means there will be much stronger winds, higher waves, and more damaging storm surge flooding than many emergency managers and homeowners planned for when they made their decisions of whether or not to board up and evacuate.
Storms like this instill fear in the hearts of hurricane forecasters because they spotlight how — despite satellites, radars, "hurricane hunter" aircraft and their legion of dropsondes, and other technological wizardry — the puzzle of what makes such storms rapidly intensify remains a mystery. And more so in this case than in others, so does how to solve the challenge of communicating to the public what all of the implications of forecast uncertainty are.
Hurricane Arthur

A well-organized Hurricane Arthur less than 12-hours before making landfall in North Carolina.
After all, it didn't take much for Arthur to transition from a nuisance type storm into a formidable threat to life and property, especially if you weren't paying close attention or didn't read between the lines of forecast discussions. (If you aren't a weather geek, then you probably weren't doing this.)
With Arthur, the National Hurricane Center (NHC) issued hurricane watches for coastal North Carolina about 36 hours in advance, which is what they are supposed to do, based on their own standards. And those watches mentioned the possibility that the storm could strengthen and move closer to the coast than initially realized, necessitating hurricane warnings, yet the dominant media message, at least at the national level, remained that the storm was likely to give the coast a glancing blow at worst.
This remained the case until Thursday morning.
Weather forecasters have had to more or less nowcast this storm since it was upgraded to a hurricane early Thursday morning, as it has gained strength steadily for the past 24 hours while moving closer to the coast than initially expected. These changes in strength, track, as well as an increase in the storm's forward speed are already having a huge effect on its impacts to the vulnerable North Carolina coastline, where barrier islands are reshaped by powerful hurricanes almost on an annual basis.
On Wednesday night, the Hurricane Center was projecting that there was a 10% chance that water levels in coastal North Carolina would exceed about 4 feet. But that was based on a storm strength and track that turned out to be too optimistic. If a storm passes just east of the Outer Banks, the winds will blow from the northeast, and the area would be on the weaker side of the weather system.
But if the storm were to pass just wet of the Outer Banks (as it now appears set to do), then there would be a flow of wind and water from the southeast, and the area would experience the strongest winds the storm has to offer. This, plus the timing of the storm, make a huge difference in predicting the storm surge, as the National Hurricane Center recently laid out in great detail on its blog:
"The exact amount of storm surge that any one particular location will get from a storm is dependent on a number of factors, including storm track, storm intensity, storm size, forward speed, shape of the coastline, and depth of the ocean bottom just offshore. Needless to say, it’s a complex phenomenon."
"Although we’re getting better on some aspects of hurricane forecasting, we still aren’t able to nail down the exact landfall of the storm or exactly how strong and big the storm will be when it reaches the coast. This means that there is a lot of uncertainty involved in storm surge forecasting."
In general, hurricane track forecasts are far more accurate than intensity forecasts, which is why the NHC has embarked on the multiyear Hurricane Forecast Improvement Project, or HFIP.
According to NOAA, hurricane track forecasts have improved by 50% during the pats 15 years, while the accuracy of intensity forecasts have not improved. Between 2003 and 2008, 24-to-48-hour intensity forecasts were likely to be off by at least one category on the Saffir-Simpson Hurricane Scale.
HFIP has the goal of reducing the average errors of hurricane track and intensity forecasts by 20% within five years and 50% in 10 years, but whether this is truly achievable is not yet known. Storms like Arthur, which is only the first of the 2014 Atlantic season, suggests that there are plenty of reasons to be skeptical.
History is full of examples of storms like Arthur (or worse than Arthur) that intensified rapidly or made sudden turns that weren't anticipated adequately by forecasters and the emergency managers who rely on them for making crucial evacuation decisions. There was Hurricane Charley in 2004, which struck southwest Florida, and Hurricane Ike in 2008, which struck the Galveston area as it was on the cusp of Category 3 intensity.
Although Hurricane Arthur is not a storm that suddenly rocketed from Category 2 to Category 5 intensity, it clearly shows the perils of relying too closely on the most optimistic forecast scenarios, and instead paying heed to realistic worst-case ones that have just as much likelihood of occurring.

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