Nelson regularly records the highest sunshine hours of any city in New Zealand — over 2,400 hours a year is normal. Summers (December to February) are warm, dry, and busy: this is when the beaches fill up, the Coast Track fills its huts months ahead, and the price of accommodation rises sharply.
Autumn (March to May) is the shoulder season locals will recommend. The weather is still settled, the parks are quieter, and the apple and pear harvest is in full swing. Winter is mild on the coast but cold in the alpine parks behind the town, with snow at altitude. Spring brings strong westerlies and a rapid greening of everything; September and October are unpredictable but often beautiful.
The Nelson Arts Festival in October and the Adam Chamber Music Festival in early February are both worth timing a visit around.