Cases of heatstroke are likely to jump as temperatures surge this summer amid Japan’s first La Nina phenomenon in six years, according to the Meteorological Agency.

La Nina, a natural cooling of parts of the Pacific that alters global weather and generally brings hot days to Japan during the summer months, is likely to develop within the next two months.

La Nina is “likely to develop by the end of August and expected to last until autumn,” Meteorological Agency forecaster Ikuo Yoshikawa said.

The phenomenon causes high temperatures by making two anticyclones, the Pacific and the Tibetan, into a layer centered around western Japan, the agency said.

The last time Japan saw the phenomenon was in summer 2010, when the country was hit by a record-high average temperature that left 1,718 people dead from heat-related ailments.

Yoshikawa, who said further observation is still needed, said the situation this year appears similar, with La Nina replacing El Nino, and high temperatures in the troposphere.

La Nina is characterized by a cooling of ocean surface temperatures in the equatorial Pacific, caused by strong easterly trade winds that blow warm water west.

El Nino acts in the opposite way, with the winds weaker or even blowing in the reverse direction to spread warm water around the equatorial Pacific, raising the surface temperature there. This often translates to colder summers for Japan.

El Nino conditions in Japan, which are believed to have ended this spring, recorded their longest interval to date, lasting eight seasons since summer 2014.

According the Meteorological Agency’s three-month forecast, which was announced Friday, above-average rainfall is expected in northern Japan in July, while eastern and western Japan, as well as Okinawa, are expected to see more fair weather in August. High temperatures, meanwhile, are expected nationwide in September.

The nation is also likely to see fewer typhoons as La Nina replaces El Nino.

This year saw no indications of typhoons in the western Pacific as of May— the first time in 18 years that not a single one was detected.

According to the Weathernews website, 22 typhoons are expected this year, against the annual average of 25.6.

Although the number of typhoons that developed under La Nina in 1998 and 2010 was roughly 60 percent of an average year, Weathernews said this does not necessarily mean less damage this year.

Information from Kyodo added

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