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Rainfall Data
10-30-2011, 11:37 PM
Post: #1
Rainfall Data
This evening I found a VERY COOL site for rainfall data!!! Temps around the islands are easy to obtain and predictable, but rainfall is a very critical issue when people want to move to Hawaii. Some parts of every island are always wet and humid (which makes them lovely for the tropical landscaping), and other parts are dry (sometimes desert-like) and sunny nearly all the time. Depending on one's temperament, knowing these facts can make a huge difference to one's comfort level and enjoyment.
It also makes a huge difference for those who plan on gardening, farming or who will live in areas with no public water service. Since water wells are rare in Hawaii, no public services means that you'll be collecting rain water from your roof to meet your household needs (it's called "catchment"). Catchment is nothing to be afraid of (if the house is properly equipped) and it's very common, particularly on the Big Island.
The University of Hawaii has this neat-o interactive map right here:

After agreeing to their copyright thingy, you can go to any island and click to a VERY SPECIFIC location, because UH has provided hundreds of data points from the reporting stations located sometimes as little as 1/4 mile apart! This is a BIG DEAL on the Big Island -- for example, the rainfall at Kona Airport is 13" a year, which is unsustainable for catchment and requires you to irrigate, yet just 2 miles mauka (uphill) in Kalaoa, you'll get around 35" a year. Since 40" is the national average for the US, in Kalaoa you won't need to water your lawn as much (the forest starts just above this zone). And just 1/2 mile closer to Kailua-Kona at the same altitude, the rainfall is 55 inches!
You can click ANYWHERE that's inhabited (not just their main stations) when in zoom mode, and an "X" will show the spot, followed by some very precise data.
I was getting very frustrated with the usual rainfall maps of the whole island, because they are charted in various "belts" and each belt covers a wide range of 25 inches or more, which is no help when you are making a critical decision for buying property. Public water is available in most subdivisions near Kailua-Kona, but we want to garden and not have big water bills. And, we like to see natural trees around us, not just those in peoples' yards!
I hope the readers here will find this useful; personally it's the most valuable planning tool I have yet seen!
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11-01-2011, 05:13 PM
Post: #2
RE: Rainfall Data
Thanks Bob for posting this great rainfall map here. This is truly a helpful tool when it comes to deciding where to vacation, where to buy property or do gardening, etc. I agree that nowhere can the weather (and rainfall) vary as much as on an island! Each square mile of land is almost like a mini continent in itself.
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11-02-2011, 04:37 PM
Post: #3
RE: Rainfall Data
I see now Bob, why it usually rains more on the beach than it does uphill in my 3rd story condo Smile Good data. At first glance I would see that it rains a great deal at Kihei during January and February but in probably the last dozen trips or so to Maui, I have never had a day that kept me off of the beach in those time periods. Last year we did get soaked at the airport getting to our rental car, but that was the only rain in two weeks. One just never knows. I always pack two umbrellas from the $ store. Being prepared is enough to scare the rain away I guess.
Ya know, like tossing salt over your left shoulder in case the wind is blowing from the southwest :lol
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11-09-2011, 02:44 PM (This post was last modified: 11-09-2011 02:47 PM by WonderinginWaikiki.)
Post: #4
RE: Rainfall Data
I found this to be a very great tool for all the obvious reasons. I don't question the rainfall data but I do question the accuracy of certain landmarks that were filled into the map.
Example: Waikiki Elementary School is located approximately one mile away from where it's located on this map. According to this map, Waikiki Elementary School is located at the site of Thomas Jefferson Elementary School instead of where it is actually located just ewa (or west) of Diamond Head and a few blocks south of the entrance to Diamond Head Crater, which is on the other side of the Honolulu Zoo.
Also, is this data based on rainfall averages prior to the droughts that Hawaii has been experiencing over the last 6 years or is that included? If it does include the last six years, then the averages would normally be several inches higher depending on the number of total years of rainfall data since the beginning of rainfall data collection.
To be honest, I don't think there can be a clear and balanced way of separating the data for "Global Warming" if you want to make any kind of case. If there was a way to do it in 10 year increments, it still wouldn't be an accurate gauge but would provide insight or a comparison of the last ten years to all the others.
Why would this be important data,you might ask? In the past, we would build and plan our cities without using such data. Years later, we wonder during a great flood why a whole community was built within a flood zone or on top of an ancient landslides or building gas and oil storage tanks in areas prone to have a lot of thunderstorms and lightning.
So this data is very important no matter what the true results may be. Having this data can and will prevent loss of life in the long run. Even if we could separate the data for current drought conditions, we still need to refer to the original rainfall data for non-drought years and rainfall.
I guess that I am just curious as to where the data would take us but not to act on that data until many years later when weather patterns could be formed or detected.
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11-09-2011, 04:38 PM (This post was last modified: 11-09-2011 05:20 PM by kaniamea.)
Post: #5
RE: Rainfall Data
Very well said, WonderinginWaikiki!

The inaccuracies in the labeling of maps are becoming more familiar to all of us, as GPS and Google Earth become an instant way that we all can verify. While I don't know the part of Oahu that you are referencing, on some maps I see the same kind mistakes for a number of Big Island landmarks, and I'm not even living there yet, LOL.

I'll have to check, but I think the rainfall data is for the current year, or if it's a rolling average, it may throw more statistical weight on more recent rainfall activity. I am aware that there have been some droughts in recent years, and the areas most affected are probably those "dry side" places which are only marginally self-sufficient in water needs, even in the good years. This is where this data can be useful as a cautionary tool. However, nothing beats consulting with the locals when in doubt!
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