Although this year's predicted strong El Niño means the Atlantic hurricane season will be a quiet one, it doesn't mean the western Atlantic will be devoid of violent storms. Case in point: Hurricane Joaquin.
The storm's intensity took forecasters by surprise when it jumped over Wednesday night to a category 3—two days ahead of predictions. The National Hurricane Center expects Joaquin will hit category 4 status either later Thursday or Friday.
A drop in wind shear and an unusually warm pool of water in the ocean have contributed to Joaquin's growth into a powerful hurricane.
Evaporation of warm water powers a hurricane and causes it to intensify, said Kerry Emanuel, an atmospheric scientist at MIT in an earlier interview. Hotter sea surface temperatures means more water evaporating into the atmosphere, loading a hurricane with more energy.
Joaquin's slow-moving nature means it has more time to power up, which helps to account for the storm's explosive growth. The hurricane will lose steam once it's separated from warm water.
"That's why they always start to die when they move over land," said Emanuel. "[It's] because they don't have that fuel supply."
All that atmospheric churning translates to turmoil in the ocean. Hurricanes drag up cold seawater, which can put a damper on things. "A lot of hurricanes don't get as strong as they could because of this," Emanuel said.
Another component that can put a stop to these fierce storms is wind shear. Those upper atmospheric winds bring drier air into the center of a hurricane, which is "like throwing cold water on a fire," said Emanuel. "It just throttles the whole engine back."
Wind Isn't The Whole Story
While hurricanes are categorized based on their wind speeds, wind isn't typically the most dangerous part of such storms. "It's the storm surge," said the atmospheric scientist—that bulge of water built up in front of a cyclone or hurricane courtesy of its winds.
It's the number one killer in hurricanes, Emanuel explained. "That's what killed people in Katrina, it's what killed people in Sandy and in Haiyan."
The researcher likened a storm surge to a tsunami. One just happens to be caused by earthquakes (tsunamis), while the other is generated by hurricanes.
Then comes wind that blows around debris. Hurricane Andrew in 1992 is an example of this. "It didn't really cause too much of a storm surge," the atmospheric scientist said, "but boy did it blow a lot of buildings down."
The worrisome thing though, is that climate change will likely increase the frequency of "the high-end hurricanes," Emanuel said. Those categorized as threes or above (the scale tops out at five).
And those powerful storms have the potential to produce a lot of rain, flooding, and strong storm surges.
An Uncertain Path
Weather models are all over the place with respect to Joaquin's exact track into the weekend, but many are predicting the possibility of the hurricane making landfall somewhere between the Carolinas and New Jersey. (See National Geographic Channel's tips on preparing for a hurricane.)
The European model—the one that correctly predicted the path of superstorm Sandy—shows Joaquin heading east out over the Atlantic ocean rather than coming ashore. (Learn why the Europeans are better at predicting the weather.)
No matter which path Joaquin takes, forecasters predict moisture from the storm will be pulled into a low pressure system heading towards the east coast. That will still give communities along much of the Atlantic seaboard a good soaking.
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