The year in Western Australia, month by month
The southern figures are the capital's: 723.9 millimetres a year over 80.4 days. The northern ones come from the tropical coast: 628.0 millimetres a year, concentrated between December and March. The scoring does not rate one half, but how much of the state is usable that month.
With almost every destination, the question is when to go. With this one, the right question is where to go on the dates you already have, because the whole state is never right at once.
That is what happens when a territory stretches over two thousand kilometres north to south and crosses from the tropics to temperate latitudes. This is not one climate with nuances: it is two different climates sharing a postcode.
01 A hundred and forty-seven against six
July is the month that shows the contradiction best. In the capital 147.0 millimetres fall over 14.8 rainy days, the year's maximum, with a mean high of 18.5 degrees. It is an umbrella month.
Two thousand two hundred kilometres north, on the tropical coast, that same month leaves 6.2 millimetres over half a rainy day, with highs of 29.0 degrees and lows of 13.7. It is by some distance the best month of the year there.
August takes it to the extreme: 2.1 millimetres in the north and 122.7 in the south. And September and October bring the north down to 1.4 millimetres, which is practically zero as measured by instruments.
The wettest month of one half is the driest of the other. In the same state, on the same ticket.
02 And in January, the other way round
In January the situation flips completely. The north receives 198.7 millimetres, its annual maximum, and February adds another 177.8. The tropical half concentrates practically all its rain between December and March.
Meanwhile the capital lives through its dry months: 16.7 millimetres in January, 13.1 in February and 9.4 in December, with barely one or two rainy days a month. The southern annual total, 723.9 millimetres, is almost entirely decided between May and September.
Curiously, the annual totals are fairly similar: 723.9 millimetres in the south and 628.0 in the north. But an annual mean here means absolutely nothing, because it describes two regimes that never coincide.
03 A Mediterranean winter in the south
The far southwest is one of the world's five Mediterranean-climate regions, along with the Mediterranean basin, California, central Chile and the South African cape. Mild, wet winters and dry, hot summers.
The mechanism is the same as in the other four. In winter the westerlies bring fronts and rain; in summer the high-pressure belt shifts south and cuts off the supply, leaving whole months without a drop.
Southern temperatures are mild even in winter, with highs of 18.5 to 19.5 degrees in June and July and lows around eight. The problem is not the cold: it is that it rains on almost half the days of the month.
04 A monsoon with cyclones in the north
The northern half lives the classic tropical pattern, with a wet season from December to March and a dry one the rest of the year. But there is an added factor here worth keeping in mind: tropical cyclones.
They form off this coast during those same months, and some come far enough south to reach the capital's latitude before turning inland, bringing damaging winds on the coast and rain to the desert.
The other figure that decides a trip is the lows. In the north, in December and January, the mean minimum is around 26.5 degrees: the night does not drop below that. In July, by contrast, the low is 13.7, which is why the tropical winter is so pleasant.
05 The months that work for everything
If the offset is half a year, there are two moments when the two halves cross at a reasonable point: at the end of the northern wet season and before the southern one starts, and again six months later.
The first is April and May. The north is already down to 25.6 and 27.0 millimetres, and the south is still at 35.9 and 86.2, with highs of 26.0 and 22.4 degrees. It is the window in which the state can be travelled end to end.
The second is September and October, and it is probably better. The north is at its absolute minimum, 1.4 millimetres in both months, and the south is easing to 79.3 and 39.5, with the bonus that this is when the southwest flowers.
06 How to choose the month
If you come for the tropical north, May to September, no hesitation. These are the months of 27.0 down to 1.4 millimetres, with highs between 29.0 and 31.9 degrees and cool nights. It is also whale shark season on the northwest reef.
If you come for the southwest, September and October. Rain drops to 79.3 and 39.5 millimetres, temperatures run to highs of 20.6 and 23.5 degrees, and the heathland is in flower after the wet winter.
And if you want the whole state in a single trip, April, May, September or October, and accept the consequence: in December and January there is no good combination. The south will be above thirty degrees and the north closed by water.
The year's four stretches
From 63.0 to 198.7 millimetres a month on the tropical coast, with lows up to 26.6 degrees and cyclone season. The south is dry, 9.4 to 20.0, but with highs above thirty.
25.6 and 27.0 millimetres in the north, 35.9 and 86.2 in the south. Highs of 34.3 and 31.7 up there and 26.0 and 22.4 down here: both halves work at once.
From 18.3 down to 2.1 millimetres in the north, with 13.7-degree nights. In the south, by contrast, 122.7 to 147.0 millimetres a month and up to 14.8 rainy days.
1.4 to 9.6 millimetres in the north and 79.3 down to 24.2 in the south, with highs of 20.6 to 26.8 degrees down here. It coincides with the southwest's flowering.
