The Japan Meteorological Agency warns that temperatures in western Japan may approach 40 °C tomorrow, July 28 [1].

This extreme weather split creates simultaneous risks of life-threatening heat exhaustion in the west and flash flooding in the east. The duality of these systems complicates national emergency preparedness during the peak of the summer season.

Forecasters said a combination of a low-pressure system and warm, moist air is driving the current volatility [3]. In western Japan, including northern Kyushu, many areas are expected to see clear skies and intense sunlight [1]. Temperatures in these regions are projected to reach approximately 40 °C [1].

Meanwhile, the same atmospheric conditions are bringing heavy rain to eastern Japan, including the Kanto interior [2]. The Japan Meteorological Agency said there is a risk of heavy rain across eastern and western Japan [2]. Some reports suggest eastern Japan may experience a mix of high pressure and sunshine, but the agency continues to warn of significant precipitation risks through July 29 [2].

Public health officials said there is a need for heatstroke prevention as tropical nights and extreme heat persist [3]. Residents in the west are urged to stay hydrated and use cooling systems to manage the heat. In the east, officials are monitoring the low-pressure system for potential landslides, or urban flooding caused by the heavy rain [2].

"Heatstroke countermeasures are necessary. Extreme heat and tropical nights continue," the agency said [3]. The agency also said that many areas in western Japan are likely to see sunny intervals tomorrow [1].

“Temperatures in western Japan may approach 40 °C tomorrow, July 28.”

The simultaneous occurrence of a severe heatwave and heavy rainfall across different regions of Japan illustrates the volatile nature of the archipelago's summer climate. When low-pressure systems interact with high-moisture air, they can trigger rapid shifts between extreme heat and torrential rain, placing a double burden on the national infrastructure and public health systems.