Sweltering, record-shattering heat wave roasts Puerto Rico

A dangerous heat wave has enveloped the Caribbean to begin June, setting numerous record highs and creating dangerous conditions for residents and tourists alike, according to AccuWeather forecasters.

Across most of Puerto Rico, AccuWeather RealFeel® Temperatures have exceeded 110 degrees Fahrenheit on a regular basis so far this month, while the actual temperature has consistently reached into the mid-90s F, shattering multiple records.

Numerous heat warnings, watches and advisories have been issued by the National Weather Service in Puerto Rico, where the electricity grid remains unstable in the wake of the destruction left behind by deadly Hurricane Maria in 2017.

AccuWeather's team of forecasters that regularly issue forecasts for parts of the Caribbean expect the unusual heat - which has a link to the wildfires in Canada and smoky skies in the northeastern United States - to last for at least another week and continue to challenge record highs in June.

A persistent jet stream pattern across North America and over the northern Atlantic Ocean is responsible for the sizzling heat in the region.

"A large dome of high pressure has been nearly stationary since the beginning of June from the eastern Caribbean into the Atlantic," said AccuWeather Senior Meteorologist Tony Zartman. "This high, sinking air has not only resulted in a lack of rain, but it has also allowed temperatures to rise well above historical averages for early June."

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With the jet stream amplified up and over the Caribbean and across the Atlantic, the atmospheric balance has resulted in a dramatic dip in it across eastern North America, home to the ongoing Canadian wildfires. This has assisted in allowing dangerous smoke to flow south into the northeastern U.S.

Higher-than-average ocean temperatures across the central and northern Atlantic are also contributing to the record heat. While this could help drive the development of tropical storms and hurricanes across the Atlantic basin later this summer and into the fall, in the short term, it will continue to contribute to the record warmth across the Caribbean.

As of Sunday, June 11, 2023.

Through the first 11 days of June, San Juan has already notched or tied four daily record highs, and at least another is in jeopardy of falling this weekend if temperatures surpass 93 F on Sunday. That record high has stood since it was established in 1974. High temperatures there this time of year are typically around 89 F, and the departure from normal has been about 4.8 F above historical averages.

Similar departures from historical averages were seen across other parts of the central and eastern Caribbean.

"In the Dominican Republic, the capital city of Santo Domingo has incredibly been 7.7 degrees Fahrenheit above historical averages so far this month," added Zartman. "Meanwhile, Saint Croix in the U.S. Virgin Islands has also been very warm, at 4.2 F above historical averages."

The intense heat has also extended into northern parts of South America. In Caracas, the capital of Venezuela, temperatures are an astonishing 13.7 F above historical averages so far in June.

As the old adage goes, it's not just the heat-it's the humidity. The abnormally high ocean temperatures in the region have driven up humidity levels.

The heat index, a legacy calculation that combines the temperature and humidity to estimate how warm it feels to exposed skin, recently peaked at 125 degrees Fahrenheit in the northern Puerto Rican town of Dorado, according to local TV meteorologist Carlos Omar.

"The higher humidity not only makes it feel even hotter during the day, but it also keeps temperatures from dropping off very much at night," said Zartman. "There have been several nights in a row during the past week (when) temperatures have not dropped out of the 80s F."

The most dangerous time for heat-related illness is at night when the body typically recovers from the excessive warmth of the day. With temperatures staying above 80 F, and RealFeel® Temperatures often not falling below 90 F all night, the stress of the heat accumulates on the body.

As of Sunday, June 11, 2023.

"My Puerto Rican family can't remember it being this hot for this long in their recent memories," said AccuWeather Meteorologist and radio broadcaster Dean DeVore. "Concerns about ongoing health issues, and the Commonwealth's continuing power grid problems since Maria, have islanders on edge about how they can keep cool in this unprecedented heat."

The patched-up power grid in the wake of Maria continues to be an issue across Puerto Rico, and recent power outages haven't helped. On Monday, more than 40,000 customers on the island lost power during greater-than-average demand, according to the Puerto Rican newspaper El Nuevo Día.

A 2021 study published in the journal Environmental Science & Technology stated that power blackouts during heat waves more than double the mortality and morbidity risk in an urban population. These heat waves, while not individually caused by climate change, have been made worse and occur more frequently due to it.

Moving forward, AccuWeather forecasters see little relief over the next several days for the heat-stricken Caribbean.

"The weather pattern is not expected to change through next week," says Zartman. "After that, there are some signs that the persistent area of high pressure could retreat off into the eastern Atlantic, allowing the heat to ease somewhat."

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