Monday, January 16, 2017

Monday 1 16 17 morning call

Just a short windsurf session for me yesterday, that's my way of giving my paddling muscles a rest...

Everything went as predicted, but the size of the waves at sunset that were a lot smaller than I suggested. Sorry about that, I'll elaborate in the buoys section below.

In the meantime, this picture of Jimmie Hepp from this gallery shows:
1) the size of the waves in the morning. The surfers is on a wave that is barely chest high, but:
   1a) judging from the wave behind, the wave was probably much bigger at the take off
   1b there's another bump in front that hides the very bottom of it, so it might actually be a few inches bigger than it looks
The one on the back is head high for what we can see, but the same 1b point applies.
I use these opportunities to clarify my way of judging the size of the waves. There should be no need, since they're quite self-explanatory, but I can see that years of use and abuse of the Hawaiian scale has left a tendency of calling the waves smaller than they are in most surfers.
2) the easterly trades that picked up just exactly how the MC2km maps predicted. It was sunny, so maybe a tad stronger, but with the correct timing. If you want to know the wind for the day and it's after 6am (when they usually gest updated), that's the website to go. Link n.17 of GP's meteo websites list on the right column of this blog, below the banners.

5am significant buoy readings
South shore

2.2ft @ 12s from 269° (W)

3.8ft @ 12s from 301° (WNW)

No direct south readings (even though 8 days ago on Jan 8 there was a tiny fetch east of New Zealand), the WNW swell is still big enough to "overwhelm" the buoys. Check the webcams, I just added another Kihei Cove webcam link that a reader sent me. The webcams section is just below the GP's meteo website list.

North shore
5.3ft @ 12s from 291° (WNW)
5ft @ 9s from 316° (NW)

5.5ft @ 13s from 309° (WNW)           
4.6ft @ 9s from 345° (NNW)
5.1ft @ 13s from 331° (NNW)

3.9ft @ 9s from 75° (ENE)           
3.4ft @ 6s from 73° (ENE)
2.6ft @ 13s from 320° (NW)
1.8ft @ 11s from 320° (NW)
The buoys this morning give me a wonderful opportunity to elaborate on the behavior of westerly swells.Let's start with the direction. Please notice how it changes from 291 at the NW buoy, to 309 at Hanalei, to 331 at Waimea and back to 320 at Pauwela. Now if the last two numbers were inverted, everything would make more sense, right? The swell wraps around the islands of the chain and loses a bit of west each time. But "nature doesn't like to be put in the cookie cutter" (epic Pat Caldwell sentence) and it leaves us wondering why the hell is it like the way it instead is.

Two possible explanations.
a) the bottom contour of the NW tip of Oahu's north shore is shaped in a way that it really refracts that particular size and period in a way that it then hits the buoy from 331.
b) the buoy readings don't have to be taken too precisely. I sample whatever last reading is on when I do this call. If you guys check them an hour or two later, they might as well be quite different.

But the most important part of this morning's readings is the size, IMO. Check the 13s component at those four buoys: 5, 5, 5, and half of 5 at Pauwela. That tells us that the amount of energy lost for refraction (and extra travel) in Maui is much bigger than the sister upstream islands.
In the NW buoy to Maui travel time and shadowing angles post (accessible through the labels section of this blog) I calculated the "geometrical" shadow line from Pipeline to Kauai as 295. The one from Hookipa to Molokai is 305 instead.
I saved the picture below a few days ago from a facebook post. It was a long term forecast of this WNW big swell that just hit. Don't get into the detailed numbers please, just notice how much more Kauai receives, then visually compare it to what hits the north shore of Oahu  and then continue to Maui's north shore. And if you feel depressed at this point, just look at the Big Island and feel better.
I am not a fan of these kind of maps. I used it in this occasion, because it helped me explain the concept, but you should not take them too literally. Big Island's southwest coast got plenty energy from this swell, for example.

Back to us, anything more west than 305 and Hookipa gets robbed of some of the energy. The bigger and longer period the swell is, the less this is true, because those can wrap around better (still losing some energy, though). So what happened yesterday afternoon is that the period went down a couple of seconds and the resulting energy that was hitting Pauwela (and Hookipa) went down accordingly.

Below are the graphs of the four reported buoys. I put an arrow on a very slight bump that happened (and that was predicted from the Surfline forecast) yesterday at the NW101 (the top left) and is propagating through the island chain. Is it going to happen also in Maui? Maybe, but with the period now down to 12-13 seconds, I'm afraid that the portion of the energy we will get compare to our upstream islands cousins will still be fractional. Stay tuned for the beach update for an indication of the size in the water.

Current wind maps shows:
1) a very strong WNW fetch
2) a hint of a windswell fetch
3) a small/weak southerly fetch

MC2km map at 7 shows strong ESE trades lurking just behind the Pauwela Point corner.

The noon map shows the strongest moment. Very offshore today, it will take some sunshine for the wind/kitesurfing to happen and it will be very gusty if it does.

PS. I made these following slight changes to the blog:
- I introduced a weekly rotation for the paying banners (the rest are old trades). Once a week, I'll move the top one to the bottom and keep the whole thing circling.
- I added a webcam to the list (kihei cove from the side)
- I was requested to add back the "donate" button, but I actually never removed it. It's still there at the very top of the list of banners.

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