Author: Matthew Cappucci / Source: Science News for Students
The Atlantic hurricane season certainly hit the United States hard this year. First came Florence. That storm dropped 91.3 centimeters (35.9 inches) of rain. Then Michael roared ashore as the third most-intense U.S. tropical cyclone to ever hit landfall. But the eastern Pacific had it even worse. As of October 22nd, this region recorded its most energetic cyclone season on record.
That big — and scary — assessment comes from Phil Klotzbach. He used to work for the National Hurricane Center in Miami, Fla. Now he works at Colorado State University in Fort Collins. There, he analyzes tropical storms and hurricanes. He calculates how much energy they release. That energy is expressed as a numerical score known as ACE. It’s an abbreviation for Accumulated Cyclone Energy. These scores have been kept since around 1970.
Klotzbach and other atmospheric scientists use ACE measurements to describe the amount of destructive force unleashed by a storm’s winds over its life. To figure it out, scientists take the maximum sustained wind speed within the eyewall of a storm. It’s measured in knots. Then they square that number. To account for variations in the storm’s strength, this process is repeated every six hours. Once a storm has fallen apart, researchers tally up the energy estimates computed from each six-hour chunk of a storm’s lifetime.
The results are pretty big numbers! To make the digits more manageable, scientists normally divide the total by ten. To see how a hurricane season stacks up, they keep a running sum and compare that year’s score to those for other years. The hurricane season is longer in the Pacific Ocean than in the Atlantic. It runs from May 15 to November 30. (In the Atlantic, it runs from June 1 to November 30.) That’s because the waters in the eastern Pacific tend to be much warmer, thanks to the structure of its ocean currents.
By late October most years, the ACE score for storms in the eastern Pacific totals around 125.7 units. So far this year, storms have churned out a staggering 305 units! That’s how scientists know it’s been a really bad year.
These numbers, by the way, come from tallies for storms in the ocean basin that’s east of the International Date Line. (This imaginary north-south line passes through the middle of the Pacific Ocean.) West of there, tropical cyclones are called typhoons. Near the Date Line, there’s a natural lull in storm activity.
There may be more to come
Keep in mind, there is still another month left in the eastern Pacific hurricane season. Despite this, 2018 has already claimed the top spot since recordkeeping began. It’s above the season-long 295 ACE units counted in 1992, and the 297 tally for 2015. In the coming weeks, this year’s ACE total could top 350 or 400! Simply stated, we’re in uncharted territory.
So what churned up so much Accumulated Cyclone Energy? At least 10 major hurricanes developed in that region this year. Each reached Category 3 status or greater. That means they had winds of 179 to 209 kilometers (111 to 130 miles ) per hour. Of these, four climbed to Category 4 status. Another 3 reached the top tier — Category 5. Those potentially lethal storms boast winds stronger than 251 kilometers (156 miles) per hour. For perspective, this year is only the third in recorded history to generate three Category 5 storms in the eastern Pacific.
Such monster storms can wreak havoc wherever they strike. On October 22, Hurricane Willa was the year’s third Category 5 storm. Its winds revved up to 257 kilometers (160 miles) per hour. En…
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