Townsville’s 2018 Wet Season and what comes after

We’re officially in Winter now and I reckon we moved definitively into the Dry season a fortnight ago, so it’s worth looking back at the Wet and seeing what’s likely to happen to our water supply in the Dry.

Wet season rainfall and the year to come

Herveys Range rain radar
Here comes the rain! Hervey’s Range rain radar, 9.15 pm on Feb 20, 2018

BoM climate data reveals that our rainfall so far this year, Jan – Feb – Mar – April – May, was 118 – 285 – 343 – 10 – 2 mm, for a total of 760 mm.

Of that, 435 mm fell in the last week of February and the first two days of March when a rain depression was trapped over the city; an unusual but very welcome event which made the difference between another really  weak Wet and a nearly-average one. Continue reading “Townsville’s 2018 Wet Season and what comes after”

Nathan and other cyclones

People who live in North Queensland learn to keep an eye on cyclones as long as they exist, whether they look like being a direct threat or not. I followed the progress of cyclone Nathan, via the BoM’s Cyclone Tracker, day by day and it turned out to be a good example of their unpredictability.

The thumbnails here are screen shots from the BoM site at around noon each day from Monday 16 March until Nathan was declared ‘no longer a cyclone’ on Wednesday 25 March; click on them for larger images, as usual, or a slide show. A satellite image showing Nathan’s remnants off the Kimberley coast on Saturday 28 March completes the sequence.

Nathan, March 16
Nathan, March 16

By the time I started recording Nathan, the cyclone had formed in the Coral Sea, drifted slowly West towards Cooktown, stalled, back-tracked slightly further North and drifted South and East to be almost exactly East of its position five days earlier. The prediction at that stage (March 16) was for intensification from category 2 to 3 and a track to the South and West which might have struck the coast anywhere between Cairns and Cardwell a few days later.

Nathan, March 17
Nathan, March 17
Nathan, March 18
Nathan, March 18
Nathan, March 19
Nathan, March 19

In the event, Nathan tracked further to the North, crossing the coast just North of Cooktown as a category 4. When a cyclone moves over the land, it loses its source of energy and moisture. Wind speeds fall quickly and the storm can be downgraded from (e.g.) category 4 to 2 in a matter of hours and, if it stays over land, to a tropical low or rain depression.

Nathan, March 20
Nathan, March 20

A rain depression can still be a very significant weather event, with hundreds of millimetres of rain falling in 12 or 24 hours, but without the destructive winds.

Townsville’s “Night of Noah” in 1998 was one such event, the result of the remnants of cyclone Sid; it brought us a metre of rain in a day or so, more than enough to stick in the memory. Wikipedia has quite a big page on it, and the BoM produced a comprehensive report (pdf).

Nathan, March 21
Nathan, March 21

If the weather system moves back to sea, however, it can re-form into a cyclone. Nathan did just that after crossing Cape York, and struck the Eastern tip of the Northern Territory during the night of 21-22 March as a category 2 system.
The people of Nhulunbuy must have felt life was totally unfair, since they had suffered through cyclone Lam (bigger but not striking them so directly) only a month earlier.

Nathan, March 23
Nathan, March 22
Nathan, March 24
Nathan, March 23
Nathan, March 24
Nathan, March 24

After passing very briefly over land, Nathan tracked West along the Arnhem Land coast, just far enough out to sea to pick up more energy and remain at category 2, before dipping South-west over Maningrida on March 24. That was its last day as a cyclone. It continued over land to the South-west, passing South of Darwin and then out to sea as a low. It dumped 100 – 200mm of rain on the way, flooding remote communities and cutting roads.

The remnants of Nathan off the Kimberley coast, March 28
The remnants of Nathan off the Kimberley coast, March 28

Four general points about cyclones are worth making:

  • The Bureau of Meteorology does a terrific job of tracking and predicting cyclones. Predictions for 24 hours ahead are consistently accurate, and the cyclone’s track further into the future stays within the widening grey cone of possible tracks.
  • How much damage a cyclone does to human life and property depends as much on its track as on its strength. When Nathan crossed the coast North of Cooktown as a category 4, its footprint covered Cooktown (pop. 2500) and a few smaller communities – a total of perhaps 5000 people. When cyclone Larry crossed the coast near Innisfail (pop. 8500 and in a much more closely settled region) in 2006 as a category 4 it did $1.5 billion worth of damage.
  • Cyclones (typhoons) striking areas with greater population density, e.g. the Philippines  (and especially Haiyan), or less-robust infrastructure, e.g. Cyclone Pam in Vanuatu  often have far more dire effects.
  • Climate change fuels stronger cyclones. According to Kerry Emmanuel on RealClimate there is a “strengthening consensus that the frequency of high category tropical cyclones should increase as the planet warms.”

Basic theory and a variety of numerical simulations support this, as well as the projection that tropical cyclones should produce substantially more rain, owing to the increased moisture content of the tropical atmosphere. This is important because most destruction and loss of life are caused by high category storms and their attendant storm surges, and by freshwater flooding from torrential rains. Most of the disagreement in the literature on tropical cyclone projections concerns the incidence of weak storms, but these are usually far less consequential in spite of being more numerous.

… While Pam and Haiyan, as well as other recent tropical cyclone disasters, cannot be uniquely pinned on global warming, they have no doubt been influenced by natural and anthropogenic climate change and they do remind us of our continuing vulnerability to such storms.

First cyclone of the season

The first Queensland cyclone of the 2012-2013 season, Oswald, has been hanging round in the Gulf for the last few days. It’s not a big one and we’re a long way away from it but we’re still feeling some of its effects: gusty winds (up to 50-odd kmh), dramatic skies (no more of this boring all-blue-all-day!) and a bit of rain (about 25mm in the last week).

Most of the action is further north, of course – Cairns has had 70mm and Cooktown has had 130mm in the same timeframe – and our weather radar has very often looked like this:

Weather radar 220113That is, rain anywhere north of Paluma and only showers for us. We don’t mind at all.

The forecast at this stage is for the ex-cyclone to drift south, bringing more wind and rain to the south-east gulf and the Cairns and Tablelands regions. Again, we’re on the fringe and will get a bit of rain but not too much. Here’s hoping!

Remembering Cyclone Yasi

It’s a year this week since Yasi crossed the coast between Townsville and Cairns, affecting both cities to an extent but devastating the smaller towns, especially Tully and Cardwell, in between. It was the biggest cyclone ever to cross the Australian coastline, though perhaps not the most intense.

Our own memories of the event are of trepidation, anxiety, relief and a lot of inconvenience and hard labour. We spent hours beforehand preparing the house and yard, as best we could, for the wind and rain. We lost mains power halfway through the afternoon, cooked and ate dinner by gas stoves and lanterns, listened apprehensively as the wind built through the evening, and got as much sleep as we could during the night – which wasn’t much.

Yasi crossed the coast in the middle of the night, which meant all we knew was what we could hear: lots of wind noise, rain, and the crashes and thumps as debris hit the walls or roof of the house. The centre was far enough away so that the eye didn’t pass over Townsville, so we didn’t experience the lull and wind change that you always read about with cyclones – all we got was the gale steadily but very slowly building through the afternoon and evening and dying away just as slowly from midnight to mid-morning.

Flooded, debris-strewn garden after Yasi
The front garden soon after first light

First light revealed a mess in our yard and street but it was still far too windy to be safe to venture out – I made my first tentative foray into the street at mid-morning. What I found was nowhere near as bad as what we might have had. Trees and branches had come down, sometimes damaging roofs, but houses were essentially intact and streets were passable on foot if not by car. And we hadn’t had nearly as much water as we had expected: Yasi had slowed down as it approached the coast and arrived well after high tide, not with it, and the feared storm surge hardly happened. It didn’t bring as much rain, either, as some smaller cyclones have done.

That day and the following week or so brought the hard work and inconvenience. We had no power until, I think, the Sunday, and we had to continue as best we could with gas, candles and torches. Fridges were quickly thawing and there was no ice because no-one else had power either. The garden needed a lot of  work, clearing branches and leaves (we hired a large skip rather than wait for council collections, but we still had enough for an enormous compost heap) and cleaning out the pool; the house had to be returned to normal after our bout of lifting, packing and waterproofing; while some of us had to go back to work as soon as we could.

Here are some post-Yasi photos, taken around the house on the morning after, then on the Strand on the Sunday after, then up on Hervey’s Range, also on the Sunday. As usual, click on the small image for a larger one.

Back yard after Yasi
The paperbark was stripped and the bananas collapsed but the mango was hardly touched.
The pool and back yard after Yasi
The pool was full of leaves from the poplar gum.

Broken tree after Yasi
Broken tree in Mulligan Street

Street after Yasi
Looking down Water St: a big spiky shrub fell over but the poincianas only lost small branches.

Cafe life on the Strand after Yasi
Cafe life on the Strand after Yasi looked almost normal, in spite of heavy cleanup work going on nearby.
Cleaning up along Strand after Yasi
Cleaning up on the Strand after Yasi - note Castle Hill in the background stripped of its greenery
Bushland after Yasi
Bushland on Hervey's Range after Yasi. First impressions were that it had gone brown, because we saw trunks and branches instead of leaves, and bright.