Warm all year. Water around 26°C. Air temperatures average 24°C during the day and 20°C at night. It receives less rain than other tropical areas, and maximum temperatures average 80°F with only moderate humidity. The rainy season lasts from December to April when temperatures and humidity are higher (most extreme from January to March). The greatest number of thunderstorms occur in December and February. Annual rainfall at Nuku'alofa averages 58 inches, with as much as ten inches falling in April and as little as one inch in May and July. Vava'u is the wettest group. In contrast, during the Tongan winter (June to August), temperatures can occasionally be quite cool. The period from November to April brings on the cyclone season. Tonga averages two tropical hurricanes every year (sometimes as late as May). Severity of thunderstorms, probability of cyclones, rainfall, and temperatures increase farther north in the kingdom. During summer (especially from February to March), north winds bring heat, waves and heavy rains.