Winter in Hawaii

Rain Gauge
A rain gauge indicating over three inches of rain
I does look like we will have a white Christmas here on the Big Island. Yes it snows in Hawaii, at least atop our nearly 14,000ft mountains.

It is currently snowing with freezing fog at the summit. The morning ranger report noted that there are blizzard conditions on the summit and that the road was impassable. The road is closed to all vehicles (not just the public) and the snow removal crews will not attempt to clear the road today. I am scheduled to go up tomorrow, I do have a few things I would like to get done, this may not happen.

Continue reading “Winter in Hawaii”

A Precipitation Sensor

Getting rain or snow on the primary mirrors is bad.

Open Dome
The Keck 2 primary mirror
The normal method of detecting conditions that might lead to rain or snow is by monitoring the humidity or dew point. If the dew point approaches the current temperature, to within a few degrees the operators must close the domes. This is much the same thing as the humidity approaching 100%. Thus I have installed several new humidity/dew point/temperature sensors over the last few years. These replaced some old and troublesome equipment that had been in place for over a decade.

The problem… You can have both rain and snow occur with low humidity. Moist air above the telescope can produce rain or snow which falls into drier air at the summit level. This can catch the operators by surprise, a situation we have observed on a number of occasions.

To help detect this you can deploy a precipitation sensor, something some of the neighboring telescopes have done. The engineers over at CFHT were kind enough to show me the units they had installed during their remote operation project.

Keck Weather Mast
Various instruments atop the Keck Observatory weather mast
Yes, I just went out and bought one. Not just any old unit either… The best precipitation sensor I could locate on the market, a Vaisala DRD11A. The sensor uses a capacitive detection method. Moisture on the top of a plate will change the capacitance and trigger the sensor. The plate is tilted to allow rain to run off and heated to melt snowflakes and sleet. testing on my work bench showed this to be pretty effective and quite sensitive. Yes, you can visualize me sitting at the bench dripping water on a sensor… It worked.

Not that the project was finished there… The new sensor does not come with any sort of network interface. Rather surprising given that just about everything else Vaisala sells has either a serial interface or an ethernet interface. This sensor has just a couple simple outputs… A logic level indication of precipitation, an analog output representing roughly how much, and a frequency output representing the same thing. I needed to interface this unit to the network. As I have installed a terminal server in the rack below the weather mast, at the minimum I needed a serial port.

While I was at it there are a couple other little devices I want to install on the weather mast. These need a network interface as well. May as well put together another little PIC controller and assemble it all together in one neat little package. a few evenings of coding and I had my solution, an interface that allowed remote computer control and status read-back. How many microcontrollers do I have performing little tasks at the summit now? Quite a few.


Processing the photo I realized I could not make it green enough. If I pushed the saturation far enough to resemble reality I would be accused of over-processing the image. Yes, the ranch lands around Waimea and Waikoloa are that green right now.

The normal annual rainfall in Waikoloa is about 12 inches. Over the last few weeks we have received eight inches in our unofficial rain gauge on the front lanai. Normally summer is the dry season here, with most of the rainfall occurring during the winter months. The result is endless green across the mountainside.

As the rains have continued this last weekend, another half inch in the rain gauge, it will stay green. Eventually the rains will come to an and, everything drying out, returning the pastures golden brown again. Then, of course, the mice will come.

Waimea Green
The pastures around Waimea are currently vivid green.

A Lot of Rain

The past two weeks have seen a great deal of precipitation over normally dry Kohala grasslands. Over three inches at the house last week and another three over the last few days from the remains of tropical storm Kilo.  This amounts to over half our normal annual rainfall for Waikoloa.  The result has been hot muggy weather that has everyone complaining.

No sign of it letting up either.  Tropical depression 12E has graduated into tropical storm Ignacio with a probable path that includes the island.  Looking at the sea temperature anomaly maps gives a possible reason, the forming El Nino is stronger than expected, surprisingly warm.  Life will be interesting.

Rain From Tropical Storm Kilo
Our rain gauge showing over three inches from tropical storm Kilo

A Stormy Day

It has been raining all day in Waikoloa, a few tenths in the rain gauge as I left the house for work. In Waimea it is even worse, cool and damp, enough so that everyone is complaining about the cold. But then, island folks complain about anything under 80°.

Money Tree
Raindrops cover the leaves of the money tree
The weather was great for my mother’s visit two weeks ago. She was able to get some sun and beach before returning to the Northwest. Good thing she did not come this last week, nothing but grey skies and rain for the island. The storm is expected to last a few more days.

No progress on the lanai project this weekend, far too wet to paint. The trees in our landscape will like this rain, a steady soaking rain. Likewise the weeds will probably be doing all too well. I can turn off the watering system for a while. This morning’s shower was a tad cooler than I like, need to remember to turn on the electric backup in the solar hot water heater this evening.

Rain Gauge

Rain Gauge
A hand made rain gauge
Desert dwellers take rain seriously. Living much of my life in the Sonoran Desert has instilled a reverence for rain. Waikoloa is little different, the driest area of the island, we typically get around 10-15 inches of rain each year.

The original gauge was a cheap plastic unit that was starting to crack. It had served many years, repairs to the lanai required its removal. The board it was fastened to was beginning to rot and needed to be replaced. The plumeria were overrunning its location as well, blocking the rain.

A glass tube rain gauge ordered on eBay was the starting point. The cheap stamped aluminum base just begged to be replaced with something better. A few minutes of thought and an idea was formed. Off to the garage with the tube of glass, rummaging through the stash of supplies commenced.

The holder was assembled with the same skills and tools I use for constructing and repairing electronic devices. Copper wire and solder, with thin brass alloy used for the leaves.

A couple hours bending and twisting the wire, soldering each joint as I went. A section of one inch copper pipe stood in for the fragile glass tube during forming. Twisted wire and little metal leaves… Much classier than the stamped aluminum base supplied with the gauge.

Who says engineers are not artistic!


It looks like it may clear. There should be a few dark hours before moonrise. Maybe I can get the new astrophoto rig out and get everything working properly.

<Commence tropical downpour>

Nothing like two tenths of an inch of rain in half an hour to put a damper on astronomical plans.

Maybe it will clear later.

Scope and Rain
A tropical downpour ends plans to use the ‘scope.

Astronomers Using Keck Observatory Discover Rain Falling from Saturn’s rings

W. M. Keck Observatory press release

NASA funded observations on the W. M. Keck Observatory with analysis led by the University of Leicester, England tracked the “rain” of charged water particles into the atmosphere of Saturn and found the extent of the ring-rain is far greater, and falls across larger areas of the planet, than previously thought. The work reveals the rain influences the composition and temperature structure of parts of Saturn’s upper atmosphere. The paper appears in this week’s issue of the journal Nature.

“Saturn is the first planet to show significant interaction between its atmosphere and ring system,” said James O’Donoghue, the paper’s lead author and a postgraduate researcher at Leicester. “The main effect of ring rain is that it acts to ‘quench’ the ionosphere of Saturn, severely reducing the electron densities in regions in which it falls.”

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Postcard from Alaska – Grey Day

The weather can be glorious, grey and cold, or simply miserable. I have experienced trips with nothing but sunny days and temperatures allowing shorts and sandals. Other times have brought rains that equaled anything I have seen, when it seemed the sea was both above and below. Sailing through narrow, rocky passages with nothing but radar to see the shore a few hundred feet away, shrouded in fog.

You take what you get on a trip, no way to reschedule now. Rain or shine, fog or mist, each can be beautiful in their own way to an traveler willing to enjoy the experience, whatever life brings.

Grey Day
A grey view out the wheelhouse window of the Chrisara on Chatham Straight, 3 July 2004