High heat and humidity could push heat indices above 108°F across Puerto Rico, Vieques, Culebra and the U.S. Virgin Islands
A period of dangerous heat is affecting portions of Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands today, August 17, as a Heat Advisory remains in effect from 10 a.m. to 5 p.m. AST. The National Weather Service in San Juan says heat indices could exceed 108°F, creating an elevated risk of heat-related illness, particularly for people who are sensitive to heat or lack reliable cooling and hydration. (National Weather Service)
Heat Advisory Covers Multiple Caribbean Islands
The advisory includes portions of Puerto Rico, along with Vieques and Culebra, and the U.S. Virgin Islands, including St. Thomas, St. John and St. Croix. Communities in urban and coastal areas can experience especially uncomfortable conditions as high temperatures combine with elevated humidity. (National Weather Service)
Why the Heat Feels More Dangerous
The biggest concern is not simply the thermometer temperature. High humidity slows the body’s ability to cool itself through evaporation of sweat. As a result, the heat index can climb considerably higher than the actual air temperature.
According to the latest National Weather Service forecast discussion, heat indices are expected to remain above 108°F in some locations, with the elevated heat threat continuing through much of the workweek. (National Weather Service)
Who Is Most Vulnerable?
Although anyone can become overheated, certain people face a greater risk during prolonged periods of extreme heat.
Those who should take extra precautions include:
- Older adults
- Young children
- People working outdoors
- Athletes and people exercising outside
- People without effective air conditioning
- Individuals who become dehydrated easily
- Anyone spending extended periods in direct sunlight
Pets can also be affected. Provide animals with plenty of fresh water and shade, and avoid prolonged activity during the hottest part of the day.
Puerto Rico Heat Impacts
Across Puerto Rico, urban and coastal communities may experience the greatest combination of heat and humidity. The advisory covers areas including San Juan, Ponce, Mayagüez, Carolina, Caguas, Fajardo and numerous surrounding communities. (National Weather Service)
Outdoor workers and people traveling between communities should plan activities around the hottest part of the afternoon whenever possible.
Vieques and Culebra
The island communities of Vieques and Culebra are also included in the Heat Advisory. Visitors and residents should be especially cautious during outdoor recreation, beach activities, hiking and boating.
Being surrounded by water does not eliminate heat danger. High humidity can still make prolonged outdoor exposure hazardous.
U.S. Virgin Islands Also Under Heat Advisory
The Heat Advisory extends across the U.S. Virgin Islands, including St. Thomas, St. John and St. Croix. Communities such as Charlotte Amalie and Christiansted are among the locations included in the advisory area. (National Weather Service)
Tourists enjoying beaches, parks and outdoor attractions should take regular cooling breaks rather than waiting until they feel overheated.
How to Stay Safe During the Heat
During the advisory period, residents and visitors should:
- Drink water frequently, even before becoming thirsty.
- Limit strenuous outdoor activity during the afternoon.
- Seek air-conditioned or well-ventilated locations when possible.
- Wear lightweight, loose-fitting clothing.
- Take frequent breaks in shaded or cooler areas.
- Never leave children or pets inside a parked vehicle.
- Check on elderly relatives, neighbors and other heat-sensitive people.
- Watch for symptoms such as heavy sweating, weakness, dizziness, headache, nausea or confusion.
If someone develops severe symptoms, including confusion, loss of consciousness or signs of a serious heat illness, seek emergency medical assistance immediately.
Heat Threat Could Continue Beyond Today
The heat concern is not necessarily limited to Monday. The National Weather Service says an elevated heat threat is expected to persist through the workweek, with warm temperatures and heat indices exceeding 108°F in some areas. (National Weather Service)
Meanwhile, relatively dry conditions are expected through late Tuesday before a tropical wave approaches the region around Wednesday, potentially increasing shower and thunderstorm activity. (National Weather Service)
That changing weather pattern could bring some relief from the heat in some locations, but residents should continue monitoring updated forecasts.
Radar Watch HQ Final Thoughts
The current Heat Advisory is a reminder that Caribbean heat can become dangerous when high temperatures combine with humidity. Puerto Rico, Vieques, Culebra and the U.S. Virgin Islands should prepare for periods of oppressive heat, particularly during the afternoon.
Stay hydrated, reduce strenuous outdoor activity during peak heating and check on those most vulnerable to heat-related illness. Continue monitoring official weather updates as conditions evolve.
Stay weather-aware with Radar Watch HQ, and keep checking back for the latest weather developments, advisories and safety information.
Radar Watch HQ Top 5 Essentials for Extreme Heat
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When an Extreme Heat Watch or Heat Advisory is in effect, having the right gear can help you stay safer and more comfortable.
A compact, battery-powered fan provides cooling while traveling, working outdoors, waiting at events, or during power outages.
2. Insulated Water Bottle or Tumbler
A high-quality insulated bottle or cup keeps water cold for hours, making it easier to stay hydrated throughout the day.
A handheld misting fan or spray bottle delivers instant cooling by combining fine water mist with airflow.
Portable air conditioners, evaporative coolers (where appropriate), or high-performance tower fans can help reduce indoor temperatures during dangerous heat.
5. Electrolyte Hydration Packets or Drinks
Electrolyte supplements help replace minerals lost through heavy sweating and support hydration during prolonged heat exposure.
