The four rapid-intensifier hurricanes of 2017, compared with Hurricane Wilma of 2005. Shown are the last periods in which the hurricanes were at various levels (tropical depression, tropical storm, or Category 1 hurricane) along with the intervals from that point to the first point at which they achieved their top rating (either Cat 4 or 5). Graphic: Dr. Jeff Masters / Weather Underground

By Chris Mooney
19 September 2017

(The Washington Post) – “Maria is developing the dreaded pinhole eye,” wrote National Hurricane Center forecaster Jack Beven on Monday evening, as the storm reached Category 4 intensity.

That inward contraction of a hurricane’s eye can be one telltale indicator of what hurricane gurus technically call “rapid intensification,” although a more evocative word might simply be “explosion.” Whatever you call it, it’s something we keep seeing this year. Harvey, Irma, Jose and now Maria have rapidly strengthened — and all too often, have done it just before striking land.

It’s a dangerous and scary phenomenon that scientists and forecasters are still trying to understand.

“It’s not a common event. Typically, that occurs in maybe 5 percent of our forecasts,” said Mark DeMaria, acting deputy director of the National Hurricane Center.

But DeMaria said that this season is seeing more rapid intensification events than usual and that Maria, in particular, appears to have set a key record for hurricane rapid intensification in the Atlantic.

“Looking back through the records, Maria went from a tropical depression to a Category 5 hurricane in just two and a half days,” he said. “I couldn’t find any other tropical cyclones in our historical record that went that quickly from a depression to a Category 5 hurricane.”

That’s a big problem, because rapid intensification sets the stage for worst-case scenarios. Sadly, that’s what happened to the Caribbean island of Dominica on Monday night, hit by Maria at full Category 5 strength.

There’s little chance to warn people or for them to prepare if rapid intensification occurs, so forecasters naturally want to be able to have a handle on it — but it’s a struggle.

“One of the key issues is that it remains quite difficult to predict on a day-to-day basis. And of course, it’s something we would very much like to be able to predict, especially when an intensifying storm is near land,” said Gabriel Vecchi, a hurricane expert at Princeton University.

The National Hurricane Center technically defines rapid intensification as a wind speed increase of at least 35 miles per hour in 24 hours. All four of the most intense Atlantic storms in 2017 beat that easily:

  • On the evening of 24 August 2017, a day before landfall, Harvey was a Category 1 hurricane with 85-mile-per hour winds. Twenty-four hours later, at landfall in Texas, the storm was a Category 4 with 130-mile-per-hour winds.
  • At 11 a.m. on Monday, 4 September 2017, Hurricane Irma was already a strong Category 3 storm with 120-mile-per-hour winds. But Irma then radically strengthened further, becoming a superpowered upper-end Category 5 storm with 180-mile-per-hour winds in just 24 hours.
  • Following behind Irma in the middle of the day on 7 September 2017, Hurricane Jose was a Category 1 storm with 90-mile-per-hour winds. Twenty-four hours later, it was rated a high-end Category 4 with 150-mile-per-hour winds.
  • Beven’s “pinhole eye” language came as Hurricane Maria reached Category 4 intensity, despite having been a Category 1 just 12 hours earlier. But Maria wasn’t done. The storm would leap further to Category 5 strength, ultimately increasing in intensity by 65 miles per hour in 24 hours. [more]

The scariest thing about 2017’s hurricanes: They keep getting really strong, really fast



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