At least four people have died of heatstroke and the Japan Meteorological Agency has warned people to take precautions against an early heatwave that has enveloped the nation.The sudden spike in temperatures began on Tuesday, with Kofu reporting a high of 38.2 degrees Celsius (100.7 degrees Fahrenheit), more than 10 degrees above average for the middle of June, which is typically the rainy season in Japan. Temperatures of 37.7 degrees were reported in Gunma prefecture and 37.6 degrees in...