Best grade oil for warm climate?

I'll be changing the oil pretty soon in my 2004 prius at 85000km (approx 53000 miles). It had 77000km on the odo (and a fresh oil change) when I got it so this will be my first oil change.

I was wondering what would be the best viscosity to use given that I'm in a warm climate. It's very unlikely to see anything under 5C (40F) here and it may be operated in ambient temperatures up to about 45C (113F).

Any suggestions?

 

Yep I think 5w-30 should cover a pretty wide temperature range but I was wondering if 10w40 or something like that might be even better in a hot climate?

 

Mid-north coast, NSW.

 

Ok looks like I'll go with 5w30 then. Actually I've already got a 5L bottle of Valvoline Durablend 5w30 (it's a "semi-synthetic" oil) at hand. I'm hoping this will be at least as good or better than whatever the dealship has been using (previous owner had all the servicing done at the dealer). I'll drop by the dealer tomorrow and pick up a filter and drain plug washer and change the oil sometime over christmas new-year.

BTW this Durablend 5w30 is what I was originally planning on using but then I noticed that 5w30 was the lightest grade of that product sold in Australia. It (valvoline durablend) is also available in 10w30, 10w40 and 15w50 grades. (See Valvoline - Automotive Products ). That's what started me thinking that maybe one of the heavier grades could be better for summer.