Sally officially experienced “rapid intensification,” a term that refers to a storm’s maximum sustained winds increasing at least 35 mph in 24 hours or less, according to the National Hurricane Center.

Sally saw top winds increase from 60 to 100 mph in 12 hours, from 5 a.m. to 5 p.m. Monday.

Rapid intensification is one way scientists believe the climate crisis is impacting hurricanes, with warmer waters helping storms grow stronger and do so faster.
Hurricanes Hanna and Laura earlier this year also rapidly intensified before making landfall in Texas and Louisiana, respectively.

Rapid intensification is especially dangerous when in happens in the 24 to 48 hours before a storm reaches land. That’s because you can go to bed at night anticipating a Category 1, then wake up to a Category 3 major hurricane that brings impacts far worse than earlier anticipated.

And that is exactly what we’ve seen with Sally, Laura and Hanna.

It’s creeping toward land

Sally is moving at 2 mph — slower than the average human walking pace.

Hurricanes and tropical storms are moving slower around the planet, says a study from National Oceanic and Atmospheric Administration scientist James Kossin, who analyzed hundreds of storms in all basins over decades.
Hurricanes are slowing, which could be a big problem

The slower a storm moves, the more rain it can drop on a particular area, and the longer severe winds have to weaken infrastructure.

There was a 10% decrease globally in storms’ forward speed between 1949 and 2016, though there was some variation among ocean basins, the 2018 study in the scientific journal Nature showed.

Recent storms that have devastated the US — such as Hurricane Harvey in Texas and Hurricane Florence in the Carolinas — have moved extremely slow, allowing for massive rainfall totals and flooding.

It looks like Sally will follow that trend.

It’s packing a lot of rain

Historic flooding is possible with Sally, the National Hurricane Center said, because of the amount of rain that is forecast over 48 hours beginning Tuesday.

Scientists are very confident the climate crisis is making storm rainfall worse by increasing the rate at which it falls, as well as the amount of rain a storm can produce.

A woman is evacuated by canoe in Houston after Hurricane Harvey dumped record rainfall in 2017.

“Simply put, warmer air holds more water vapor,” said Kossin, an atmospheric research scientist at NOAA’s National Centers for Environmental Information.

Gulf of Mexico water temperatures are largely above average, and the Northern Hemisphere just experienced its hottest summer on record. That allows storms like Sally to hold more moisture and produce more rain.

With Sally, three to four months’ worth of rain could fall before the storm leaves the region Thursday.

CNN meteorologist Judson Jones contributed to this report.

source: cnn.com

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