Why So Cold?

With summer now officially on our doorstep, it’d be right to say that it’s time to hang up your steamer. This isn’t the case if you living on the East Coast. Over the last week or so, the water temp has turned bitterly cold for the time of the year. Surfers are ditching the boardies and vests and returning to sporting a steamer. We hit Stu Nettle from Swellnet with a few questions to find out what the hell is going on and how long these chilly waters will last.

Where is this cold water coming from?
“The cold water isn’t coming from any particular direction; it’s an up welling from deep below the surface. It’s caused by a phenomenon called ‘Ekman Transport’.”

How long will it be here?
“Till we get a break in the relentless nor-easters which cause the upwelling. It’s blowing south today which may stop the upwelling, but then it’s predicted to swing back to non-stop nor-east till the end of the weekend so it’ll definitely come back. Better get the steamer out or harden up.”

What is causing it?
“When the wind blows from the northeast the Coriolis Force (the same force that causes wind to blow clockwise around low pressure systems in the Southern Hemisphere) causes the water surface to move at 90 degrees to the way the wind is blowing. So if you think about it, the wind is coming in from the northeast yet the surface of the ocean is being pushed out to sea to the southeast. Something has to replace the surface water and that is colder water from below.”

Is it an ongoing thing, will the cold waters return this summer?
“The warmer waters will definitely return. As above, just wait for a break in the nor-east cycle. Unfortunately we have a stationary high-pressure system exacerbating the process.”

Is it a common thing for this time of year or is this unusual for the east coast?
“We usually get one or two of these events every summer and each time it will last for two to three days. This is actually the second one we’ve had in a month so there may be a chance that we see more upwellings than usual this summer. Keep your steamer handy.”

Will these cold currents bring winter like swells with them?
“Nup. No chance. It’s created by nor-east winds so the best you can hope for is 3-4 feet of nor-east swell.”

Stu then emailed us a quick scientific explanation of what was really happening. We didn’t understand one word of this technical jargon:

“A quick elaboration for any office nerds: As weather watchers will know, winds roughly follow the isobars on a synoptic map. Yet, if you think about it, winds should blow directly from a high-pressure system to a low-pressure system – that would have it blowing across the isobars. However, the Coriolis Force ‘knocks’ the wind 90 degrees to the left, so rather than blow across them it blows parallel to them.

The Coriolis Force does the same thing to water. Wind blows on water, but rather than flowing in the same direction as the wind, the water is ‘knocked’ 90 degrees to the left. Hence, the cold-water upwelling is scientifically related to the synoptic winds that give us swell.”

Tags: Stu Nettle, Swellnet