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#1442036 - 23/11/2017 06:13 Sydney vs Port Macquarie
James West Offline
Cloud Gazer

Registered: 20/11/2017
Posts: 4
Does anyone know why Sydney's overnight lows are so much higher than Port Macquarie's? In July, August and September this year [2017] Sydney's overnights averaged 4.2c higher. So far for November [today's the 23rd] we're still averaging 2.5c warmer. I can't detect any topographical reasons, nor anything to do with ocean currents. Even if Port Mac's temps are registered at the airport, that only 2 miles from the ocean. Observatory Hill is 4 miles inland, on a grassy knoll near the Coathanger. Probably moderated somewhat by the harbour, but that doesn't explain the discrepancy. Is this the "heat island" effect?

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#1442038 - 23/11/2017 06:55 Re: Sydney vs Port Macquarie [Re: James West]
Steve777 Offline
Weatherzone Addict

Registered: 20/10/2011
Posts: 3782
Loc: Artarmon (Sydney North Shore)
Observatory Hill is a particularly warm site for a number of reasons:

1. It is on top of a local hill, about 40 metres above sea level. It is mostly unaffected by inversions.
2. It is close to water, i.e. the Harbour.
3. Urban heat island effects. This would be excacerbated by being close to the approachhes to the Harbour Bridge and to the CBD.

I believe that the current Port Macquarie site is located at the Airport, on the edge of town and a few kilometers inland. I expect that it would be in a fairly flat, low-lying area and affected by inversions on fine Winter nights.

For comparisons between Sydney and other sites, I think that Olympic Park would be better.

Maybe someone with more expertise would like to comment.

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#1442051 - 23/11/2017 09:04 Re: Sydney vs Port Macquarie [Re: James West]
Befour Offline
Weather Freak

Registered: 30/04/2015
Posts: 184
Loc: Kingsford (Sydney)
Would agree with what Steve has said, OH would be massively influenced by urban heat island effect and being so close to the harbour.

I know that when I do venture into the city for a dinner or something of a night it is often very noticeably warmer in the city than at my place near Ashfield and that distance isn't huge.

Something else that could have come in to play is that we experienced an extended run of dry and clear nights through these months along the east coast which lead to cooler than average night time temps, I would say in particular for more inland stations.

Stations with a more maritime influence would have recorded temperatures above average due to above average Sea surface temperatures during this time - just for a bit of fun I have compared a few sites being Observatory Hill (Maritime Influence through the harbour) Port Macquarie, Smoky Cape (Maritime influence and not far from Port) and then Canterbury here in Sydney for another inland location - the numbers from these locations do seem to support this theory with October being the outlier with all locations recording above average temperatures but this was also a month where we started to see some more rain.

Here is a screen shot of the quick comparison I put together with each sites averages for 2017 and in brackets the difference from the average temps)



Edited by Befour (23/11/2017 09:07)

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#1442059 - 23/11/2017 10:29 Re: Sydney vs Port Macquarie [Re: Steve777]
James West Offline
Cloud Gazer

Registered: 20/11/2017
Posts: 4
Thanks to both Steve777 and Befour. I suspected the heat island effect must be the major factor. I live in Elizabeth Bay, and there are quite a number of tropical palms and plants growing in gardens here. I've never seen a frost around here, but I used to see them when I lived near Chatswood. I don't know if either of you are aware, but sometime in May (!) this year the botanical Gardens staff replanted the four Malay dwarf cocos palms from the hothouse to the open gardens. They're not looking too good right now - one looks like it's had it, but two of them look like they might have a chance of surviving (at least until next winter). We'd be unlikely to get another winter next year as mild as this last one was near the coast.

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