While Hong Kong is an all-year-round destination, the most popular time for tourists to visit is from mid-September to end February, when the weather is cooler.

However, for photographers, a better time might be around early September, Summer time. That's when Hong Kong has more typhoons

Why? Because air in Hong Kong is highly-polluted. It's rare to get clear blue skies. During Summer, it's hot and humid and you will sweat like crazy. However, the monsoon winds help to clear the bad haze. The skies are especially beautiful and air is surprising clean on days just after a typhoon visited.

In short, summer typhoons are bad for tourists but great for photographers (if you can wait long enough)

If you decide to come during September, try to time yourself to come during the Autumn Festival (which lasts for only a day in September, check the Chinese Lunar calendar for the specific date). There will be lantern decorations for this festive day in Hong Kong.

Spring comes in mid/late Feb - the weather turns rainy, foggy and the humidity can be as high as 99% in March.

If you want to see more "chinese" things, come during chinese new year (festive decorations last for weeks)