The major local current off the New South Wales coast is the East Australian current which brings warm water from the Coral Sea into the cooler Tasman Sea, keeping the sea surface temperatures off Sydney relatively warm. The nearby Tasman Sea and the extensive inlets and waterways of the Sydney region also help to modify the coastal climate. As a result, Sydney has a temperate climate with warm, sometimes hot summers, cool winters and mainly reliable rainfall all year. Sydney's climate is generally cool to mild in September and mild in October. September and October are the first months of spring, with mild to warm temperatures during the day and cool to mild nights - although the occasional hot day and cold night do occur.
Humidity is moderate, both during the morning and afternoon.
Only a few fogs develop in Sydney's west and these dissipate early. Thunderstorms are generally few, increasing in frequency in late spring. Such strong winds favour southerly to westerly directions. During October strong winds are more prevalent from the south and sea-breezes become more common. Windy days and mild temperatures characterise a typical spring day in Sydney, making it generally a season of good overall air quality and, compared to some previous Olympic cities, the climate for Sydney can be expected to be mild.