A Rainy Month

Speaking of all the rain, the NOAA published their December 2008 precipitation summary. Bob Dylan once said you don’t need a weatherman to know which way the wind blows, but these people are tracking the numbers and putting out useful information. Well, it’s useful to farmers and water supply planners, I just like being aware of the long term trends.

Here is what they said about Kaua’i:

All of the gages across Kauai recorded above normal rainfall during the month of December. Though not nearly as wet as the record-breaking conditions of March 2006, it was the wettest month of 2008 at all locations island-wide. The USGS gage on Mount Waialeale recorded the state’s highest monthly total for the month with 59.21 inches (130 percent of normal) and the highest daily total of 13.75 inches on December 13. […]

The wet December conditions helped nudge several gage totals into the near normal range for 2008. Breaking down the distribution, available gages along the north and northeast slopes finished the year in the near to below normal range while most of the gages in the east- and south-facing slopes ended up in the near to above normal range. As expected, Mount Waialeale’s 351.66 inches (83 percent of normal) topped all totals statewide for 2008.

In summary, we had normal rain for the year, but much of it happened in a few storms in December. For example, the year’s total at Lihue airport was almost exactly average, but fully half of the rain there came in December. After a year with varying degrees of drought, all the rain came at once, meaning less of it soaked into the ground to replenish the groundwater and more of it washed dirt into the streams and out into the ocean.

The north shore was uncharacteristically less rainy overall. They had about the same rainfall as the east side this year, when normally they’re 50% wetter. But I’m always amazed by Wai’ale’ale: one foot of water in one day, six feet of rain for the month (as tall as me), and almost 30 feet for the year. Assuming that density is sustained over one acre (210 feet square), that’s twice as much water as in the Shamu pool at Sea World [PDF] (“one of the largest marine animal pools in the world” containing 14.5 acre/feet of water by my calculations).

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