The best time to visit Kota Kinabalu is March to October, when the west coast of Sabah enjoys its dry season with lower humidity, calmer seas, and reliable sunshine — ideal for hiking, island-hopping, and diving.
March to May is arguably the sweet spot: post-Chinese New Year crowds have thinned, the mountains are clear, and sea conditions around the marine park are excellent. June and July bring the hottest and driest weather and coincide with the Mount Kinabalu Climbathon and Harvest Festival season — book mountain permits many months in advance if visiting at this time.
August to October remains largely dry and is a popular window for experienced divers visiting Sipadan, where visibility is often highest from July to October.
November to February marks the northeast monsoon. Kota Kinabalu's west-coast location buffers it from the worst rain (unlike Sandakan on the east coast), but expect short heavy downpours, choppier seas, and occasional cancellations of ferry services to the marine park islands. Prices drop noticeably and the city itself is still very visitable — many travellers find the tradeoff worthwhile.
For Mount Kinabalu, avoid January and February when the summit plateau is frequently rain-soaked and visibility poor. April, June, and September are considered the most reliable months for a clear-sky summit.