The end of November marks the official end of Atlantic hurricane season — 97% of tropical cyclone activity occurs in the six-month between June and November.
That's a relief after an intense few months of destructive storms. The 2017 Atlantic hurricane season was a top-10 hurricane season by most metrics. It set a few all-time records as well.
The chart below shows how 2017 stacks up to other years, thanks to data collected by meteorologists at Colorado State University's Tropical Meteorology Project.
The season was "extremely active", to use the National Hurricane Center's technical term. In an "extremely active" year, storms have to generate at least 152.5 units of accumulated cyclone energy — a measure of storm intensity, duration, and frequency. 2017 hit 226, mostly due to storms in August and September, when Harvey, Irma, and Maria devastated parts of the Caribbean and US.
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An "extremely active" season also has to meet two out of these three conditions: 13 or more named storms, seven or more hurricanes, and three or more major hurricanes. We hit all three, with 17 named storms, 10 hurricanes, and six major hurricanes.
Here are some of the all-time records set this year, according to CSU:
- maximum sustained wind speed of 185 mph
- more than 60 inches of rain
Overall, it was a rough year — one that exceeded forecasters' expectations, even though most called for an above-average season. The exact factors that made it so active are still under investigation, though warmer-than-normal sea surface temperatures likely played a role, since that allows storms to pick up intensity. A lack of strong wind shear, which can break apart storms, is considered a factor.
Hurricanes can still happen after November ends, however. As the National Oceanic and Atmospheric Administration notes, "there is nothing magical in these dates."