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We made it through Hurricane Sally, mostly bruised and battered. Sadly, some lives were lost. Areas of big property damage were focused along the coasts and shorelines. I hope for you Sally was “just” an inconvenience and disruption. The landfall at night was scary since howling wind, gusting for long periods, adds to the stress, fear and unknowns of trees falling, projectiles striking our homes or roofs being ripped off. Power outages and roads blocked by downed trees were more than an inconvenience.
Sally was an extremely difficult hurricane to forecast because of weak steering winds, leaving multiple scenarios of strengthening and paths as options. The slow motion is what allowed tremendous rain amounts closer to the beaches, and it kept extreme winds there much longer than expected of a typical hurricane.
A day before landfall, it became clear Sally was not going to Louisiana. “But the forecast changed from what you said yesterday,“ some people commented on Facebook. Yes, it did, for the same reason that when you are using GPS driving across the country, you constantly hear, “recalculating.” As new data arrives, you must recalculate your projection. Don’t plan tomorrow based on yesterday’s forecast.
“What category will it be?” That’s the same question as, “Are we there yet?” We don’t truly know the landfall category until landfall. Relying on a category to define all threats of a hurricane is like choosing a partner based on their weight. The hurricane wind scale is only for wind speed. While years ago it did have storm surge estimates, we’ve learned storm surge often does not correlate to the category at landfall.
Rainfall? Tornadoes? The category tells you nothing about those either. The category also does not tell you the duration of the storm. A category 2 storm that stalls on the coast could be more devastating than a small, fast-moving category 3 storm.
The difference between categories is 1 mph, but the difference within categories can range from 15-25 mph. A high category 1 and a low category 1 are not the same.
In any given location, Sally could have been the worst storm ever to strike, as all hurricanes have unique structures and each of us defines “worst” differently.
Compare Hurricane Sally to Hurricane Ivan, which made landfall in virtually the same spot of Baldwin County exactly 16 years prior. Sally had maximum sustained wind of 105 mph, a forward motion of 3 mph and a hurricane wind radius of 40 miles. Ivan had maximum sustained wind of 130 mph, a forward motion of 13 mph and a radius of 105 miles. That reinforces that no one statistic on a hurricane gives you the single answer to what the impact will be in one location.
As with all storms, the maximum wind is typically estimated since rarely is there a weather sensor in the path of the highest wind. Statistics often have to be estimated by interpolating known measurements and sometimes finding data after the storm that was not available in real time.
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