The waters around Australia aren't nearly as warm as they were
last year

http://www.bom.gov.au/social/2011/09/chalk-cheese-cats-and-dogs/

Put it this way, we've had around 18 La Niñas since 1900, yet only
about three have been as significant as the 2010-11 event.

"So what about 2011-12? Word on the street is that we might have another La
Niña?" I hear you say.

Well that's true. There is an increased chance of La Niña. But the real $64
million question is - how do things stack up against last year? And more to the
point, are the odds as high for a big wet?

Well, first of all, let's look at last year. And let's narrow it down to this
week last year.

This week last year the central Pacific Ocean (which is what every climatologist
and their ocean array looks at) was about 1.4°C cooler than normal. That's a
lot! So what has the temperature been this week (i.e. right now). Drum roll
please ... about 0.6°C cooler than normal or 0.8°C warmer than last year.

To put the -1.4°C (this week last year) and the -0.6°C (this week) into context,
in the tropical Pacific during September about 70 per cent of the time the water
is within 0.9°C of its normal temperature (23.7°C). In other words, last year
was "WOW!!!" And this year is "Well, that's kinda interesting, I might keep an
eye on that..."

Yep, a lot warmer around Australia last year than this year.

So lump that all together, and what do you get? Last year at this time: a raging
La Niña, a ripping negative Indian Ocean Dipole and record warm sea surface
temperatures off our northern coast (indeed 2010 brought the warmest ocean
temperatures on record around Australia).

For Aussie rainfall, that's tick, tick and tick. And BIG TICKS at that. As one
colleague said in our September 2010 monthly climate meeting: "If it doesn't
rain now, Australia can pack up and go home." And right he was. Rained cats and
dogs.

This year we have a neutral Pacific Ocean (granted on the 'La Niña' side of
things and a La Niña remains possible), a positive Indian Ocean Dipole and
average to slightly cool temperatures off our northern coasts. For rainfall
that's a two-thirds tick, a cross and bit of a dashed line.

But as we said at the start, it's all about shifts in the odds when it comes to
climate and the impact of climate drivers. Yes, we'll expect rain this summer
and yes, the drivers can and indeed will change, but when you compare where we
stand right now to where we were last year it's like chalk and (a little bit
chalky) cheese.