Planning for the weather is a good way to make your trip to Greymouth relaxing and enjoyable, especially when you’re splurging. The hottest months are usually February and January, with an average temperature of 15°C, while the coldest months are July and August, with an average of 9°C. The rainiest months in Greymouth are May, December, October and September, with each month seeing an average of 262 mm of rainfall.