Monday, December 03, 2012

The Wisdom of Crowds?



Last week everyone was buying into the idea that Sunday was going to be an "epic" day of frostbite sailing in Newport. 

It was going to be warm, way up in the 50s!!! (That much was true.)

It was going to be blowing 12-15 knots from the S or SW.  "All" the forecasts said so. Champagne sailing conditions. Woo hoo!

When I arrived at Newport at around 11:45am there as no wind at all. Zero.

One of my friends was very confused. What's going on? All the forecasts say there should be 15 knots.

Well. Not quite all the forecasts.

As I wrote last year in All Weather is Local (I Hope), just because the overall wind forecast for Narragansett Bay is X it does NOT mean that your little corner of or sheltered harbor off Narragansett Bay will see X. And the higher the resolution of the weather model you use, then the more likely you will be reading an accurate forecast for where you actually sail.

True, most weather forecasts had been forecasting 10-15 knots from the S or SW for Narragansett Bay on Sunday. But when I checked SailFlow on Sunday morning and looked at the WRAMS 2km model (instead of the default that SailFlow uses) it did predict that there would hardly be any wind at all at Rose Island before 4pm.  Rose Island is the closest SailFlow site to our sailing area in Brenton Cove but it is outside the harbor so, if anything, I would guess it has more wind than our racing area.

Here is what was actually recorded at Rose Island.



We raced from just after 1pm to about 3:30 pm. There was no wind at all as we rigged from 12-12:30pm. We launched in a SE zephyr just before 1pm. There was a very light breeze from the SSE for our first race. Then the wind went round to the SW but shifted back to the S as we started our second race around 2pm. And then there was a reasonably steady and slightly stronger S wind for our third and final race around 3pm.   I think the winds we experienced where we were racing were actually even lighter than the winds recorded at Rose Island.

What do you think?

Is there a wind forecast that you trust?

Do you have the same suspicion as me, that for short course racing the higher resolution models are more useful?


2 comments:

Baydog said...

All I know, is that around 2-2:30 on summer afternoons, it honks hard on the Barnegat Bay, consistently, every hot summer day. And in the winter months, it starts much earlier. Fleet 413 may consider coming south early Sunday mornings in the winter. I've got extra beds......

Tillerman said...

Well, yeah, in the summer we get a sea breeze too on many days. I wasn't aware of the phenomenon of an earlier breeze in the winter in New Jersey.

I heard a couple of sailors explain our lack of breeze as due to a wind higher up that somehow wasn't reaching down to the water. Certainly it looked like there was breeze higher up as the flag on top of Fort Adams seemed to be in stronger wind than we were experiencing. It was a warmish day after quite a cool week. Is there some physical explanation why those temperature conditions might inhibit a breeze from filling in at sea level?

On the positive side, this was a very unusual day. There aren't many winter days at Newport that have such light winds.

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