“Weather Window my %#%$# !!!”, I used to say jokingly for the first days pursuant to our arrival to New Zealand, after a very uncomfortable passage from Fiji.
Jokes apart, there was a lingering question in my mind: “Was it indeed a Weather Window, or Not?”
This is what I will explore on this post, in addition to sharing our leanings from this episode.
And I will start with the answer: YES, IT WAS A WEATHER WINDOW.
A safe passage from the Tropics to New Zealand generally entails such conditions that:
- a vessel shall be able to accomplish the entire route without meeting or getting near the influence area of a Low Pressure, Trough, or Frontal System.
- the above is even more important South of Latitude 30 – the last 1/3rd of the voyage
- (one corollary of the two conditions above is that the Forecast needs to be stable)
- and in the case of a sailing boat, there should also be useful winds for sailing an appreciable amount of the route
One known situation when the conditions above can be found is when a long High Pressure system traverses from West to East just below Latitude 30, and over New Zealand.
This is exactly what we saw via the forecast and had for our passage from Fiji to New Zealand: a long, well established High, which we “rode” from beginning to end, without ever crossing or getting near Bad Weather. In fact, the weather wasn’t bad at all during the voyage. Neither were the seas.
- (Below): Animation of our Passage vs Surface Pressure (Forecast at the day of departure). Note how we “rode the High”, as we intended
- (Below): This next animation shows Rain around the area of the Passage – note that we pretty much managed to avoid bad weather systems along the way
And yet, we had a miserable ride.
So, what happened ?!?
Well, let me start with the definition of “Miserable Ride” for the purposes of this post:
- we found ourselves sailing hard upwind for the first 2/3rds of the way, precisely when the winds were the strongest
- waves, while not too high (3 meters at the most), came at a diagonal orientation to our route and were very, very steep, causing intense pitching and hard slamming against the seas
- conditions above caused an unforeseen amount of water to cross our decks
- being not prepared for all this, some breakages occurred and we got far more seasick and discomfortable than anticipated
The above is certainly NOT what we were expecting before departure: a Reaching Ride, with winds blowing just ahead of our beam, and waves running perpendicular to our route, making little impact to our motion.
Having had time to “digest” the experience, and going through all the data we collected before the passage, I believe to have been able to identify the components that contributed to this situation.
1.) BEDAZZLEMENT AND WISHFUL THINKING:
Fiji has fast, inexpensive internet and thus we had access to a lot of data to go through while planning for the passage. Moreover, in hindsight, I was anxious with the anticipation of the incoming Long High Pressure system. As I shuffled through the information available, my attention was on the big picture aspects of the Window: was the High going to materialize? Would it be stable for long enough? Would there be residual effects from any nearby bad system, like a large swell? And as I processed each new weather data on my two simulation software, I misjudged one detail that they were showing to me: that wind direction would be far more Upwind than a Beam Reach, as we expected.
Technically, a well-trimmed yacht can start sailing at angles ~30 degrees off the wind. But that requires lots of tension and attention of equipment and crew to happen. In practice we find that Pesto starts sailing well at angles higher than 45 degrees off the wind. But that is in protected waters. What we would quickly discover on this passage is that with waves, and winds above 20 knots, 45 degrees off the wind is still way too tight. Not that Pesto can’t sail – she can – but the motion is just too uncomfortable, and speed gets compromised. In fact, it was only after the winds moved backwards of 60 degrees from our bow that conditions started to get reasonable onboard.
2.) JUMPING THE GUN:
Once the Long High was confirmed on the Forecast, we had to decide when to depart. An earlier departure would entail milder winds and seas, but at a tighter direction (that is, more Upwind). If we waited and let the High move a bit more to the East, then winds would be more favorable, albeit a bit stronger. The caveat of waiting is that the forecast could deteriorate for the later stage of the voyage. It was a gamble. We found that a proper compromise would be a departure on Tuesday Morning.
But then I pulled a local forecast on Sunday and saw the possibility of rain during departure – starting at the early hours of Tuesday. With that, I decided to depart on Monday Afternoon instead. That brought two unintended problems:
– in the afternoons, thermal winds accelerate and wrap around Fiji’s big island. As a consequence, we caught straight headwinds as we exited the pass, forcing us to sail Westward of our route for many hours, which then required us to sail even closer to the wind afterwards to return to the intended route.
– By departing some 12 hours ahead of plan, we caught the High westward of originally planned, and this meant the winds would be at a slightly tighter angle than what we saw in the simulations
3.) WATCH OUT FOR THOSE CURRENTS:
This is a topic that I looked as a secondary aspect of our voyage planning. But out there it revealed to be so important that I will come back to it on a dedicated post, pursuant to this one. For the time being I will mention that:
- for planning, I looked where the currents would be against us or on the same direction, and took note of related waypoints to avoid or take advantage of the currents where appropriate
- I didn’t however pay much attention to the currents running transversally to our route, and that was a problem
In the past, whenever a transversal current threw us off-route on a downwind passage all I had to do was flick the autopilot a few degrees and compensate for the effect This is not so easily accomplished when sailing close to the wind, though. That’s exactly what happened during our first day off Fiji, when a strong west-going current threw us off route, costing us precious degrees upwind to compensate for the effect afterwards.
4.) GOTTA HAVE FAITH IN THE HIGH:
The forecast told us that winds would start coming from a more relaxed direction on the later stage of the passage, meaning that we could point slightly to the west of NZ during the first days – slightly less upwind than on the straight-line route – because we would have leeway to compensate for that upon the approach to the island. But the tight upwind conditions of the first days, coupled with the west-going currents, made me fearful that we might loose New Zealand (that is, be too far West of it) should the High not do what was forecast and the winds not come from a more relaxed angle.
Here is a comparison of a straight-line route (which we pursued) versus a round one, going westward first and then turning more East on the approach to NZ, concomitant with the winds rounding Northward as the High moves along:
5.) DIDN’T SEE THAT COMING:
Even tough the Low/High pattern down South was the centerpiece of my weather analysis, in hindsight I should have paid more attention to another feature that was brewing just to the North and atop of us. Spanning for thousands of miles on a diagonal line all the way from the Salomons to Tonga lies a zone of perennial instability called South Pacific Convergence Zone, or SPCZ. Everybody who sailed the western side of the South Pacific is familiar with it. Under it weather is always unstable, rainy, and prone for the formation of small frontal systems and lows. The SPCZ moves up and down along the year, on a cyclical movement. And when sea surface temperatures are lower than normal (La Niña), it tends to move further South. That’s what happened during our departure. The SPCZ was right above Fiji, and expected to move a bit South the following days (that’s in fact what triggered our leaving earlier, to avoid its rain). But in addition to the threat of rain, I strongly believe the SPCZ had another, more important effect. It seems to have partially “squashed” our High on its Northeastern quadrant, causing the winds to accelerate, and also to come more from the Southeast. I believe that if the SPCZ were further North, our High would have been more Round in shape, and our winds less strong and more from the East – thus more benign to us.
As odd as it was to our expectations, this passage has been of great learning value to us. Here’s what we took out of it:
- Offshore, anything – wind or waves – coming from ahead of the beam feels and is “Upwind”
- The tightest “Upwind” apparent wind angles that are attainable for us are:
- If winds <15kts —> 50 degrees
- No less than 60 degrees if windspeed >15kts
- “Upwind” passages with winds >15kts will entail significant heeling, intense motion and lots of water on deck. Prepare accordingly.
- Currents play a major role on upwind passages and need to be understood and accounted for before leaving port (more to this on a dedicated post)
I was pleased to use the Predict Wind software – my first time. It integrates four forecasting models, and the route simulation is elegant. But my primary sources of decision-making data are still:
- Raw Gribfiles obtained from the GFS model via Saildocs: stable, and best long-term information I know
- WindyTy: information of a different Model, outstanding medium/short term local prediction
Specific to the stretch between the Islands and New Zealand:
- Departing when a High is not in place can be risky: we have seen Lows forming quickly in the area, and they turn bad
- Highs can be spotted way in advance using available forecasting tools (I will write more about this on a coming post)
- Once the High is present, timing it is very important:
- Departing too early means more time sailing “Upwind”, but more certainty over the forecast
- Waiting for the High to pass over NZ seems to enable more favorable wind angles, but entails higher risk of a Low forming at the end of the forecast
- It also pays to add some Westing to the route, for the same reason
- Keep an eye on the SPCZ. It can spoil the weather window (rain, less stability of the forecast, more southerly winds)
Despite all the discomfort we had, it was worth every bit of it to come here. The little we have seen and experienced of NZ as of yet has everything to be praised.
And, speaking of praise, I want again to highlight how grateful we are to own Pesto. Out there she showed us what she is made of and for.
2 Replies to “What Happened ?!?”
Nice clear story Alex. 60 degrees true I take it? Apparent wind angle gets smaller the faster you sail. This does make a fair difference. Sail balance is important to prevent rounding up a bit in gusts. That’s when the big slams start happening. So your mainsail should start luffing slightly, about 10 degrees, before your jib does. This gives your jib power enough to turn the bow downwind and keep the boat on course. In stronger winds the gap between optimum angle of attack of your two sails should be Increased. Flat seas small gap. Rough seas big gap. Getting this balance right improves the comfort big time.
Howdy Frans, Sylvia ! The wind angles I mentioned in the text are Apparent. Hope you are enjoying the beautiful Bay of Islands . Cheers
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