Mount Waialeale

Waterfalls around the caldera

The "Wall of Tears" in the crater of Mount Waialeale

The summit of Waiʻaleʻale features a tropical rainforest climate (Köppen Af), with substantial rainfall throughout the course of the year. (Bodin 1978: 272) quotes 460.0 inches (11,684 mm) per year figure as being the 1912–45 average, an average that quite possibly will have changed since then, while The National Climatic Data Center quotes this figure as a 30-year average.[4] The Weather Network and The Guinness Book of Weather Records (Holford 1977: 240) quotes 451.0 inches (11,455 mm) rain per year, while (Ahrens 2000: 528) quotes 460 inches (11,680 mm) as the average annual rainfall at Mount Waialeale and (Kroll 1995: 188) claims 510 inches (13,000 mm) falls here. Similarly, The Weather Network and the Guinness Book of Weather Records quote 335 days with rain here while (Simons 1996: 303) suggests that rain falls on 360 days per year.

The local tourist industry of Kauai has promoted it as the wettest spot, although the 38-year average at Mawsynram, Meghalaya, India is higher at 467.4 inches (11,870 mm). Both Mawsynram and Cherrapunji in Meghalaya are recognized by the Guinness Book of World Records as having higher average rainfall. Mawsynram's rainfall is concentrated in the monsoon season, while the rain at Waiʻaleʻale is more evenly distributed through the year.

Several factors give the summit of Waiʻaleʻale more potential to create precipitation than the rest of the island chain:

1. Its northern position relative to the main Hawaiian Islands provides more exposure to frontal systems that bring rain during the winter.
2. Its peak lies just below the so-called trade wind inversion layer of 6,000 feet (1,800 m), above which trade-wind-produced clouds cannot rise.
3. The summit plateau is flanked by steep walled valleys over 3,000 feet (910 m) deep on the three sides most consistently exposed to moisture bearing weather systems. These serve to funnel and concentrate any available precipitable water directly towards the mountain.
4. The steep cliffs of the mountain's flanks generate intense orthographic lift, causing the moisture-laden air to rise rapidly – over 4,000 feet (1,200 m) in less than 0.5 miles (0.80 km) – This combined with the 'barrier' of the trade-wind inversion, serves to very efficiently squeeze almost all of the moisture out of the incoming clouds directly over and immediately downwind of the peak.