G'day all,

A newbie here tho' been reading on and off for a while, thinking my first post.

OK. Why does only a Northerly wind cause the upwelling and dropping of the inshore coastal water temps?
Why does not a Southerly cause a similiar effect causing the water replacement ??

I would think (logically ??) a Southerly brings in the colder water.....

I also notice it has been a few degs. warmer only a couple of hundred metres out off the beach of late.

I assume you are talking about the NSW coast.

The wind's drag produces a surface current in the direction of the wind. But over time (several hours) the effects of the earth's rotation causes the current to deflect to the left of the wind direction. Additionally layers below the surface are deflected increasingly so. Look up Ekman Spiral for a detailed explanation of this.

The net result is after lengthy northerly or NE winds, the direction of movement of water near the surface is away from the coast - towards the SE. This causes upwelling near the coast of colder deeper water. So along the NSW coast it is common to see a dramatic drop in beach water temperatures after several days of N/NE winds.

In southerly winds the opposite occurs, the surface currents turn in towards the coast. Water well offshore the NSW is typically warmer than near shore because of the east Australian current. So several days of southerly winds will often produce a warming of beach temperatures as a result of warmer water being pushed towards the coast.

An interesting point you make about the earth's roation affecting current Mark. I had always assumed that temperature was the main factor in controlling currents.

i've consistently noticed over many years of fishing spearfishing and bodyboarding that a few days of southerlies will bring in the bluer warmer water around jervis bay and currarong, as well as blowing the bluebottles back out to sea . from looking at the satellite images of sea surface temperature it also appears that the east australian current often circulates off jervis bay back in towards the coast.

persistent westerly winds also frequently produce upwellings in this area. keep in mind that after heavy rain there will often be a thin layer of fresh/brackish water that will float above the ocean water - this will generally be much cooler also.

Thanks people.
It is an interesting one.
Your info. has been very helpful to a few of us folk down here at Mollymook SLSC.

Getting a bit tired of the NE wind and that damned Ekman! Water temperature took a 4 degrees drop in the past 36 hours.
Sydney SST .

I wonder if these eddies have any effect on La Nina? It's a bit of a self fulfilling prophecy, La Nina tends to produce lots of 'black nor'easters' which will lead to the eddies and locally cooler SSTs.

Well the eddies and Ekman seem to be working in harmony now. SST off Sydney is 17 and falling!
Looks like it is over 25 a bit further east. Cruel!

Right in time for a warm sunny weekend too!

What's wrong with low SSTs?

1) not everyone enjoys surfing wearing a 5mm wetsuit
2) pelagic fish such as marlin, mahi mahi, wahoo follow the warm currents
3)underwater visibility is generally lower, not ideal for diving
4) less energy avialable to fuel nighttime thunderstorms

on the plus side:
1) less crowded surf
2) less bluebottles

Mark gave a pretty good explanation but for further reading check this article out NFIP..

http://www.swellnet.com.au/news/125-why-does-the-water-get-colder-in-sydney-after-a-nor-easter

Everything!
Putting a steamer on and taking it off is more tiring than paddling around for a couple of hours.
If it is over 30 out of the water that steamer gets very uncomfortable very quickly.
In extreme events people need medical treatment for shock and hypothermia from the water; using up valuable life saving resources.
Plus
Stronger seabreeze due to temp gradient blows everything in your face - sand, salt spray, water spray etc.
The wind chill can get a bit much coming off 16 degrees water.
Sea fog rolling in makes the beach a dull and cool place on an otherwise warm and sunny day.
I'll stop there.

Low SSTs would actually produce a hot, dry summer around these parts CW... be careful what you wish for! Climate would be similar to Southern California, pleasant if you're 100 yards or less from the beach but roasting further inland.

Yesterday I went for a surf in the wetsuit and for the first time in many days it started to feel just a little too warm. Last weekend I took the kids to the beach and it was cold. The water colour is always a dead giveaway, a dull green/gray instead of blue.

There was a massive decaying Jellyfish that left many people with an itchy present.

With the sustained E-NE winds onto the NSW coast the BoM's BLUElink models are going for another upwelling event off the Hunter and Illawarra this week.
Very disappointing as the SSTs have only just started to climb into the 23-24 range.

The upwelling is having a disastrous impact on the NSW beaches south of about Port Macquarie at the moment. The SST off Batemans Bay has fallen to 15.9ºC from the low twenties a week ago.

A nasty shock for holiday makers awaits in the brine!

Have you checked out Sydney's SST this morning? has shot up to almost 25c!!! Batemans Bay has also shot up from the low of 15c yesterday to be sitting on 18c.

Well Sydney SST still staying mostly in the 24-26 degree range. I hope it stays like that; I never enjoy that initial cold shock when I enter the water.
That stubborn eddy off the central coast and the upwelling are still menacing the coast. Poor old Batemans Bay is still freezing.

Seems that the fickle eddies and upwellings are a perennial curse for the NSW coast. The current water temperature off Crowdy Head is a numbing 15 degrees - http://www.mhl.nsw.gov.au/www/wave_temp_crowdy.htmlx (will update). A nasty shock for locals and tourists.

This is despite the look of an express train current transporting water down from the bath waters of the Coral Sea - http://imos.aodn.org.au/oceancurrent/SE/latest.html (will update).

Glad i just bought a springsuit lol. As a pool swimmer anything lower then 24 feels cold to me, 16 is just stupid.

The water off Crowdy Head has been amazingly cold - it seems to have been stuck around 16 deg since I first looked at the Manly Hydraulics Lab site about 2 months ago, apart from a couple a brief excursions towards 19-20. If I visit the area I don't think I'll be swimming in the ocean.

It would be interesting to see what the weather has been like at places like Harrington. Possibly often cool and foggy like Syndey beaches in early November? The nearest NSW 'coastal' stations shown on the BOM site - Taree Airport & Port Macquarie Airport - are some distance inland.

Sydney waters seem to have settled at their seasonal average of about 22 deg. I expect this means that sunny days with no strong general wind circulation will max out at a seasonal 24 - 26 deg near the coast.

Crowdy Head water temperature just getting worse and worse! It was below 14 degrees for a time yesterday. Has warmed up to 14.6 at the latest report.

Wow! I have never seen the water temperature this low, ever, off NSW.
11ºC in January!!

WTF? Hopefully the trend continues towards winter when the Tasman will freeze over and NSW is blanketed in a metre of snow.

Crowdy Head SST still gone crackers at 12 degrees this morning.

I wonder if there are any reports of hypothermia or cold shock heart attacks around Seal Rocks or Forster way.

im going to guess that the Crowdy head boy has been missreading for a while now. I could understand a day or two of 16c water mid summer, but this is just silly. Port Mac is not overly far from crowdy head and the water temp is 21c.

MHL shows that sea temperature off Sydney has dropped to 21 since the start of the month after being around 23 since mid January. I think it's too early and too big to be seasonal cooling, so I suppose this must be upwelling.

Crowdy head has consistently been in the mid teens for months, so as Enrique says, it must be misreading (unless its measuring deeper water).

Some big fluctuations in SST off Sydney over the last couple of days - 17 deg to 24.


SST 120402 by Stevevii77, on Flickr

hmm thats pretty odd, must be a little bit of localised upwelling offshore or an error ( Swell readings are missing from the same time as those dips). Im in the newcastle region and near shore temps were buitiful on fri/sat mornings.

The Sydney bouy must be catching the western edge of that large anticlockwise eddy.
Water temperature now 24-25°C in the brine off Sydney.

The new mhl site is loading veeeeeery slowly for me. They may have to tweak this page - http://new.mhl.nsw.gov.au/data/realtime/sst/Sydney as the image is cut off at the right where the temperature is shown. You have to right click > View image to be able to see the temperature.

Enrique,those water temps sound good,iam having three weeks at Corlette in May GDL

Looks like MHL has fixed the SST measuring device off Crowdy Head (near Port Macquarie, NSW). Looks quite warm for this time of year, but now seems reasonably consistent with Coffs Harbour and Sydney:


crowdy_temp by Stevevii77, on Flickr