Tag Archives: forecasting

Waiting for Oma

This “wet season” has turned out to be a pretty dry season. No, a VERY dry season. In previous posts I’ve mentioned we had 1mm of rain in January. So far in February the rain gods have managed 35.5mm, which is slightly less than two tenths of bugger all in this part of the world. I’ll show you what I mean. This graph shows cumulative rainfall per month per year over the last ten years. 2019 is that tiny yellow bump at the bottom.

Mind you, these things can change very quickly hereabouts. Townsville, which is usually a pretty dry place nicknamed ‘brownsville’ was absolutely flooded just a few weeks ago. I mentioned those floods a couple of weeks ago in the post entitled ‘a typical Australian summer‘. We did ask nicely if they’d share, and I’m sure they would have been delighted to oblige but it doesn’t work that way. Townsville is about 1,100km north of Hervey Bay, so the system would have had to come down the coast to reach us. It didn’t. It moved out to sea, where it became Tropical Cyclone Oma.

When the old lady (Oma means grandma in Dutch) started moving towards Hervey Bay we got all excited. Not that we particularly wanted all the wind and such, but we did like the idea of rain.  Mind you, Oma was a cat 3 at its worst, then downgraded to a 2, but it’s wise not to underestimate the power of a cyclone.

Here’s the Bureau of Meteorology’s (BOM) best guesses for the cyclone’s track on the 19th.

This is a very good indication of how well the weather bureau, with all its fancy computers and wonderful algorithms, can predict the path of a cyclone. In this diagram the most likely path takes it round about through Fraser Island.

We got a cyclone warning and everything. Expect over 100mm of rain per day for the next several days, perhaps more. Clean up your yard, empty your gutters, make sure you have emergency supplies in case you’re cut off and/or there are power outages.

Emergency supplies

So we bought a couple of cans of baked beans, a packet of mixed nuts, Cadbury’s favourites, and stocked up on Scotch. Then we tidied up the yard. Pete took garden refuse to the tip and we put away our garden furniture and anything else that might have turned into a projectile.

The wind picked up on Thursday afternoon, but the clouds scudding up the coast from the south missed us – and most other people’s properties.

On Friday morning the BOM’s cyclone chart looked like this. Oma looks as though she’s going to stall and then head north again, well out to sea. If she does cross, they’re guessing poor old Townsville and Cairns which have both had quite sufficient for this wet season, thanks all the same, will be in for a little bit more inundation.

So… we’ve still had no rain. Windy and dry is very hard on plants and many of ours are suffering.

If any of you are in to pagan rituals, offerings to the rain gods, naked dancing, weird chants and whathaveyou, any offerings or supplications on our behalf would be gratefully accepted.

Seems to me if all the meteorologists were given a coloured marker and then blindfolded and asked to put a dot or several on a map of Queensland, they might well have ended up with a similar result to those projection charts. And although I know ‘weather’ and ‘climate’ are two different things, if the algorithms they use to predict one cyclone’s path are in any way analogous to the climate models that predict the climate in one hundred years’ time… well, make your own conclusions.

I remember years ago watching a wonderful documentary about the Chaos theory (entitled ‘Chaos’). It talked about the development of the mathematics around fractals, and the work of Benoit Mandelbrot whose name was given to the basic mathematical formula that produces the wonderful patterns (the Mandelbrot set). In the early days, computers were used for weather forecasts. Even then, when the best of computers weren’t a match for the processing power of the phone in your pocket, a computer did a faster, more accurate job than a human. The algorithms were complex and calculated figures to nine or ten (or something) decimal points. One day something went wrong and the forecasters lost their data, although they did have the final results. They re-entered the figures, using only three decimal places. The results they obtained were vastly different to what they got from the raw figures, which led to the question ‘why’ that leads most ground-breaking science. Which goes to show that tiny fluctuations can make huge differences. The plotting for cyclones is a great illustration of that truth.

Fascinating stuff.

Oh – and I’ve nearly finished that book.