Florida seems to be getting hit from all sides. The ocean is so hot that people can’t cool off in it. Insurers are pulling out of the state. The governor is in a knockout fight with both Disney and Donald Trump. Dust carried all the way from the Saharan Desert is in the air above Floridians’ heads.
Actually, that last one’s fine. It is, in fact, normal. The dust that’s coming to the state now is part of a regular cycle called the Saharan Air Layer that, as my colleague Robinson Meyer recently wrote, has been delayed this summer, contributing to the weirdly hot waters off Florida. But it’s not just the dust: to understand what the summer in Florida — and the Southeast at large — is going to look like, we have to turn to West Africa.
Let’s start with the dust. The dust storms that make up the Saharan Air Layer start out in (surprise!) the Sahara desert and can be as big as the lower 48 states before they weaken as they move across the ocean. When they hit Florida they make the air about a mile above the ground extremely hot and dry, while the air below remains soupy and humid. That hot, dry air a mile up is essentially a cloud-killer: any potential hurricanes would dissipate in those conditions, but so do the thunderstorms that would otherwise bring some cooling rain to the state.
For the most part, the dust isn’t anything to worry about, said Jason Dunion, a meteorologist and field program director for the National Oceanic and Atmospheric Administration (NOAA), though there might be a dip in air quality that people in sensitive groups — anyone with a lung condition like asthma, or senior citizens — should watch out for. The current dust storm will move on in a few days, and another will arrive a few days later to take its place. Unfortunately, the dust won’t quite do much in terms of cooling down the ocean.
“The world’s oceans are out of balance from where they’ve been for the last 125,000 years,” Ben Kirtman, professor of atmospheric sciences at the University of Miami, told me. “We’re seeing warming in the global oceans that is really quite bonkers.”
Exactly what is causing the ocean to warm — as in the literal physical effects behind that warming — will no doubt be the subject of many papers to come, Kirtman said, but there’s little doubt that anthropogenic climate change is the root cause.
That warmer water has many effects, the first being that the water off Florida is essentially now a hot tub, so the ocean breeze blowing into cities like Miami doesn’t have the cooling effect it usually does. That raises the heat index, putting people at risk of heat stroke. Higher ocean temperatures are also putting marine life — particularly coral reefs, which support thousands of sea creatures — in danger, as The New York Timesreported this week.
Then there’s the way warmer oceans impact hurricanes. This year marked the start of an El Niño, the weather pattern that usually brings less intense hurricane seasons. But, Kirtman told me, “the Atlantic is so flipping warm that the El Nino effect might not give us a weaker hurricane season.”
This is where we return, again, to West Africa. The dust, the hurricanes, the ocean temperatures: all of these are deeply, intricately connected.
“The hurricane nursery for the Atlantic is just south of the Sahara,” said Dunion “More than half the named storms we get in the Atlantic come from that nursery. So it’s a really important place to look at.”
Many hurricanes are born right off the coast of West Africa, between the Sahara and an area known as the Sahel. The hot air from the Sahara collides with colder air caused by storms in the Sahel, creating what Dunion called “tropical waves” that ripple outwards. These are the seedlings of hurricanes.
A warmer ocean sees more evaporation, which moves water vapor up through the atmosphere and usually intensifies hurricanes. This is true throughout their life cycle, and the waters off Western Africa, while not quite as warm as they are near Florida, are also much warmer than normal — in the high 70s or low 80s Fahrenheit, Dunion told me, and “80 degrees is that magic number where once we get to that temperature it's very conducive for exchanging energy from the ocean to the atmosphere.”
That heat means the hurricane nursery below the Sahara Desert could produce some especially strong storms, especially once the dust storms stop. “There’s a switch point in mid-August where the dust outbreaks start to subside.” Dunion said. “That may help open a window to make the environment much more juicy to support some of these storms,”
So the hurricanes could start especially strong, and will grow even stronger when they bump into the warm waters off the coast of Florida. Together, that could negate the effects of the El Niño; NOAA has predicted a near-normal hurricane season for this year, with somewhere in the range of 12 to 17 storms, in part because of the warmer oceans offsetting the El Niño.
That would be striking: if NOAA’s predictions hold, we’ll be in for a summer defined by the worst effects of an El Niño, like searing heat, without any of the hurricane-mitigating benefits. But, Dunion told me, the weather is ever-shifting and there are still many unknowns.
“What we don’t know is what the future is going to look like in the next month,” he said. “Will these dust outbreaks kind of ramp up really quickly? Will the sea surface temperatures settle out? That part is still a mystery. We can monitor it, but predicting exactly how it will play out is the humbling part of being a meteorologist.”
Courtesy of U.S. Forest Service
