SASEBO NAVAL BASE, Japan — U.S. military bases were reminding residents to be cautious outdoors Wednesday as a deadly summer heat wave accompanied by high humidity continued in central Japan.

Temperatures were well into the 90s in some areas by midday, according to the Japan Meteorological Agency, with humidity rates and temperatures combining to create a heat index to make it feel even hotter.

On several U.S. military bases, the weather has triggered “black flag” alerts that bar most outdoor activity.

The weather has caused the highest number of heat illnesses and injuries among Japanese since the government started keeping the records in 2008, the Japan Times reported.

Heat has killed 132 and sent more than 31,000 to hospitals in Japan since the end of May, the country’s Fire and Disaster Management Agency announced this week.

About half of the 31,579 treated at hospitals were 65 or older, the Fire and Disaster Management Agency reported.

So far, the heat hasn’t caused a rise in the typical number of summer heat injuries reported to U.S. Naval Hospital Yokosuka, spokesman Ben Avey said.

“Any treatment we have provided has been on par with our normal summer expectations,” Avey said in an e-mail response to Stars and Stripes.

Any temperature above 80 degrees activates the military’s heat warning index, which announces conditions with colored flags and determines what activities are safe.

Yokosuka Naval Base, Marine Corps Air Station Iwakuni and Camp Fuji reported black flag conditions, meaning temperatures exceeded 90 degrees. Physical training and strenuous exercise was suspended, and outside work was limited to emergency and security activities.

Meanwhile, temperatures Wednesday remained in the 80s at Yokota Air Base and Camp Zama in the Tokyo area, Sasebo Naval Base in southwest Japan, Misawa Air Base in the north and on the southern island of Okinawa.

Those bases had fewer restrictions on activities but at least required outside workers to take a 10-minute break every hour.

The hospitals and bases were stressing hydration and safety in the heat, base officials said.

“Definitely you can be outside but take precautions,” said Lt. Cmdr. Veronika Dimeo, head of the industrial hygiene department of the Yokosuka hospital.

Drink plenty of water, wear light clothing and plan activities during morning or evening when it is cooler, Dimeo said.

Temperatures are expected to remain high through the middle of next week and in some areas increase, according to Wednesday’s Japan Meteorological Agency seven-day forecast.

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