Puerto Rico Is so Hot This Week, It’s Astonishing Some Meteorologists

Parts of the U.S. territory reached a “life-threatening” heat index of 125 degrees Fahrenheit on Monday, driven by a combination of an intense heat dome, El Niño and climate change.

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People wait in line for a flight out in a sweltering San Juan Airport in San Juan, Puerto Rico on Sept. 29, 2017. Credit: Jessica Rinaldi/The Boston Globe via Getty Images
People wait in line for a flight out in a sweltering San Juan Airport in San Juan, Puerto Rico on Sept. 29, 2017. Credit: Jessica Rinaldi/The Boston Globe via Getty Images

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Puerto Ricans are no strangers to heat.

Even on its coldest winter days, the Caribbean island and largest U.S. territory rarely sees daytime temperatures below 70 degrees Fahrenheit. But Puerto Rico is so hot this week that it’s baffling some weather experts, who warn that other parts of the world will likely experience similar extreme heat this year as climate change and an exceptionally strong El Niño drive global temperatures to historic highs.

In a series of tweets Monday, Florida-based meteorologist Jeff Berardelli warned of “life-threatening heat” in Puerto Rico, with conditions on the island becoming “so hot that some meteorologists are astonished.”

The heat index—which combines temperature with humidity—soared above 100 degrees Fahrenheit across much of the territory on Monday, with parts of Puerto Rico reaching a heat index as high as 125 degrees. High humidity combined with high temperatures can be especially dangerous since less sweat can evaporate off your body to cool it off. That heat is expected to persist through at least Tuesday, according to the National Weather Service, which issued an excessive heat warning across the island, urging Puerto Ricans to “take extra precautions” to stay cool while outside.


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Berardelli linked Puerto Rico’s extreme heat spell this week to several overlapping factors, including the formation of a fierce heat dome just east of the island, a strong El Niño weather pattern amplifying heat waves and other extreme weather and climate change generally making the oceans warmer. Tropical oceans, he said, have warmed roughly 2 degrees Fahrenheit since the Industrial Revolution.

The high temperatures might also be getting impacted by what Berardelli called a “wavy jet stream,” when the fast flowing air current that moves around the upper hemisphere of the planet gets interrupted and wobbles like a spinning top rotating off kilter. It’s the same mechanism that has also caused the polar vortex to shoot down into southern states in the U.S. in recent winters, and scientists believe climate change is playing a role in that interruption.

There’s a lot of work being done to figure out the link between climate change and the wavy jet stream, Berardelli said, adding that “the loss of sea ice and uneven heating at the poles is likely a factor” in that dynamic.

Ultimately, Berardelli said, Puerto Rico’s heat wave shouldn’t be viewed as an isolated incident, and he warned that other parts of the world should anticipate similar hot spells in the coming months. “As we go deeper into 2023 and El Niño intensifies, we should expect a stunning year of global extremes which boggle the meteorological mind,” he said. “The base climate has heated due to greenhouse warming and a strong El Niño will push us to limits we have yet to observe.”

It’s a grim prediction that several other scientists have made for this year as well.

Last month, the United Nations’ weather agency warned in a major report that the combined forces of climate change and El Niño will likely drive temperatures to record highs in many parts of the world over the next five years. And a peer-reviewed study, also released last month, warned that a fifth of the world could live in dangerously hot conditions by the end of the century.

For Puerto Rico, the rising heat is compounding other climate-related threats. Studies have shown that Caribbean islands are particularly vulnerable to climate change. Rising temperatures are driving up the dangers of heavy rainfall and powerful storms in the region, where many governments struggle to recover in the wake of disasters due to a lack of resources. The situation is only made worse by high energy costs related to importing fossil fuels and crippling debt that has become all too common for Caribbean island nations and colonial territories.

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In fact, much of Puerto Rico is still recovering from Hurricane Maria, which crippled the island’s power grid in 2017 and sparked an ongoing fight over the future of the island’s energy infrastructure. Even as billions of dollars in federal aid flow to the U.S. territory to help rebuild its infrastructure, hundreds of thousands of residents continue to face regular power outages every year. Such blackouts can be dangerous during a heat wave, preventing people from keeping cool with air conditioning or making it difficult to store perishable medicine like insulin, which needs to be refrigerated.

By Monday night, Puerto Ricans were already complaining online about the heat, with some saying they’ve never experienced such a severe heat wave before.

“My town is surrounded by mountains and lots of vegetation,” posted one Twitter user, who said she lived in the rural town of Villalba. “It’s usually colder than most towns in Puerto Rico, but let me tell you that it’s been EXTREMELY HOT. It’s gone beyond 100 degrees. It’s insane.”

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Measured in parts per million, that’s the concentration of carbon dioxide that federal scientists measured in the atmosphere from their Hawaii observatory last month, officials announced Monday, making it one of the largest annual May-to-May increases in CO2 levels on record.

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