The Meteorological Agency says a Foehn phenomenon will add to a high pressure system, causing temperatures to soar and leading to dry conditions on much of the Pacific side of eastern and northern Japan.
Daytime highs could hit a record 36 degrees Celsius in Maebashi City, Gunma Prefecture and 35 degrees in Chichibu City, Saitama Prefecture.
Our bodies are not used to overheating as early as May. This means we face a heightened risk of heatstroke.
It is important to take regular breaks from work and exercise to hydrate and to keep indoor temperatures under 28 degrees.
Information on the latest regional heatstroke risk advisories, along with advice on preventive steps, is available here.