Researching Big Island Rainfall: The University of Hawaii’s ‘Rainfall Atlas of Hawaii’

Buyers moving to the Big Island frequently ask our agents and our Relocation Coordinator about rainfall. Some buyers are looking for a consistently warm, dry, sunny climate. On the other hand, because many homeowners (especially in East Hawaii and those who live off-grid) rely on rainwater catchment tanks for their water supply, these buyers need to clearly identify where there is consistently abundant rainfall. Farmers and ranchers also benefit from ample rainfall, a necessity to their agricultural endeavors.

The Hawaiian Islands present some interesting rainfall patterns due to topography, tradewinds and other factors. The resulting rainfall can be dramatically different from location to location, even over short distances. Here on the Big Island, tradewinds blow from the East-Northeast direction, resulting in abundant rainfall conditions on the windward slopes of the mountains. Leeward coastal areas receive significantly less rainfall. For those trying to determine what area would be most suitable, accurate rainfall maps are a useful resource.

The University of Hawaii’s Rainfall Atlas of Hawaii

The University of Hawaii’s Geography Department has recently released the online version of the Rainfall Atlas of Hawaii – complete with an Interactive Map enabling users to pinpoint and zoom in on specific areas and corresponding data, as well as to identify patterns over larger areas. Maps showing annual rainfall totals are available as well as maps with monthly mean rainfall totals.
Mean October Rainfall - Island of Hawaii*The above map is for the month of October. Visit our Rainfall Map page to view the Mean Annual Rainfall map for the Island of Hawaii. To view and download more maps, visit the Rainfall Atlas of Hawaii’s Downloads page.

Rainfall Mapping – Then and Now

Measuring and mapping of rainfall in the Hawaiian Islands began as far back as the 19th century. By the end of the century there were nearly 106 monitoring stations. Rainfall monitoring sites today number over 1200. It’s important to note however, that despite the seemingly high number of rain gauges there are still large remote areas with no rainfall measurement. Expert methods of extrapolation are used in these areas to determine the best possible estimates.

Thanks very much to our own Blake Howell, R(S) for bringing this fantastic new website to our attention. To have this online resource at our fingertips is an amazing asset to everyone living here in the islands, as well as to those off-island considering purchasing real estate or visiting here. Exploring it was particularly fun and interesting for me. Before moving to the Big Island, I spent several years as part of the US Navy’s Meteorology and Oceanography Command, so I’ve witnessed the evolution of weather technology over the years and greatly appreciate the ability to view such detailed rainfall data for the Hawaiian Islands right from my desktop.

Other Maps Available on Our Website

Big Island Lava Flow | Big Island Land Use | Hawaii County Tax Map Key (TMK) Zones


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