PARIS — European teams say they are more prepared than ever for a hot and humid World Cup, training in saunas, planning to soak their jerseys in cold water before games and working with doctors to design the perfect hydration formula for each player. Even though the tournament is held in Brazil's winter, stadiums in the tropical north will be warm, with temperatures often above 30 Celsius (85 Fahrenheit). And many games will be played under the afternoon sun, so they can be broadcast in prime time in Europe.