The Highs and Lows of Passage Planning

Oceangybe

Why are we still in New Zealand? by Ryan

A brilliant sunrise wafted over New Zealand the morning of 21st April, 2008, accompanied by an ice cold South West wind – a perfect wind to blow Khulula northwards. North, away from the encroaching winter, into the balmy island paradise that is the South Seas. Names like Tanna, Vanuatu, Fiji, and New Caledonia beckon to us, urging us to drop the land locked umbilical cord and take the 1800 km jump across the stormy ocean north of New Zealand. Our meager equatorial wardrobes are beginning to fail miserably in trying to hold back the cold. We all feel like ducks out of water, as each passing week brings more chill, more cold, more rain. The sails, bimini’s and other cover aboard Khulula hang limply in the New Zealand rain, and if you look close enough, you can almost see Khulula silently shivering as she floats in the chilly water.

It was a go. In 24 hours we would be gazing at a disappearing New Zealand over the stern our trusty vessel. With all the hard work done, the crew was anxious and excited for the voyage. With the dingy deflated and lashed on deck, the provisions purchased, accounted and stowed, all berths set up for offshore passage making, the duty free diesel topped up and all water tanks filled, all that remained was to check out of customs, hoist the sails and point Khulula’s bow North, and yield to the beckoning of the northern latitudes…

And yet, 24 hours later I sit here typing this to the whoosh of pressure washers and the tap of hammers as boat owners tinker with their boats. Outside I can hear the hum of our generator charging the battery bank, and the creak of the mooring lines as the tide nudges Khulula on and off the dock. Yup, you guessed it, we are not at sea…

I am going to attempt to explain the factors surrounding a weather decision to leave a land like New Zealand that lies under the influence of three large bodies of water (the Pacific Ocean, the stormy Tasman sea and the even more stormy southern ocean) and a large hot continent (Australia). I am of the opinion that trying to pick a weather window to leave this country is like trying to staple jelly to the wall. It is an incredibly unpredictable process requiring a pile of information, a great deal of local experience and a sizeable portion of luck and timing.

To even begin this discussion, I need to outline the basic weather systems that govern the flow of surface wind. Two major weather systems, HIGH and LOW pressure systems (“HIGH’s” and “LOW’s” to the average sailor), as well as the effect of the rotation of the earth, the CORIOLUS effect, govern the flow of wind on the surface of the ocean.

HIGH’s can be thought of as atmospheric mountains – areas of stable descending air, and the source of the air that will start to move and become wind. The wind “blowing down” off these HIGH’s will seek a Low Pressure area (a LOW) in which to converge, where it will be once again lifted into the upper atmosphere. Hence, low pressure systems can be thought of as holes or “sinks” into which the wind will blow. By the time the wind reaches a low pressure area it has gained a great deal of momentum during its journey from the high pressure area and has usually attained its maximum speed. A low pressure area is an area of intense instability, with moist, rising air condensing and forming clouds, thunderstorms, large amounts of rain and general unhappy times if you are unfortunate enough to be on a small boat in the vicinity. The CORIOLUS effect causes these systems to rotate in opposite directions. In the southern hemisphere, winds will spiral outwards and counter clockwise from a “HIGH” and converge clockwise into a “LOW” (think of water disappearing down the toilet bowl). Thus, in the Southern Hemisphere a low to the left (west) and a high to the right (east) will result in a strong NE winds in the band between the two systems. The strength of the winds depends of the height of the high (the higher the pressure, the “taller” the mountain) and the depth of the low (the lower the pressure, the “deeper” the sink). Check out the Figure 8 rotation around these systems on the picture.

HIGH’s are the sailors friend, LOW’s are not. In this part of the world, HIGH pressure systems drift slowly eastwards, with low pressure troughs between them. On leaving NZ, the goal is to head north in the SW winds on the easterly side of a high, enjoy light wind and sunny conditions as the high passes over (and perhaps even motor for a while), then continue north as the wind goes easterly as the HIGH passes below you. Simple right? NO! The other factor is to look for a HIGH that is not too high – better to leave with the passing of a smaller mountain, than a large one J.

So, what happened yesterday? Everything was just peachy with a beautiful forecast for the next 72 hours – light winds, good weather, a nice stable sail through the beginning of a high pressure system. Thereafter the prediction was for the usual easterly “trade winds” to set in 600 miles north of New Zealand, and theoretically above the low pressure systems of the lower latitudes. At this time of year, the likelihood of serious low pressure systems originating in the tropics continues to decline and becomes more and more remote into May, June and July. From April through July, the theory is to use the security of the relatively predicable HIGH to leave the scary lower latitudes, and by the time the HIGH passes you will be in the statistically more predictable safe zone of the trade wind belt, 600 miles+ North of New Zealand.

7am found Hugh, Brys and I huddled over the computer, pouring over the seven day forecast. Anticipation and apprehension heavy in the air, we were about to make the final departure decision. In my hand was all the completed paperwork for NZ customs and all was looking like we would be happily motoring out into the Bay of Islands with the hour.

OH NO, what’s this? A new LOW in the forecast, six days away. Not only a LOW, but a tropical LOW. The kind of LOW that turns into a tropical cyclone which is, statistically, still possible this late in the cyclone season. Wow. OK. Pause, reflect. WHY? Frustration. OK. Let’s analyse this. The questions begin: Why did the models not pick this up yesterday? Is it really going to happen? What are the chances? Will we be far enough north when it begins? Is the timing accurate? Will we be able to get above it? What happens if we can’t? Are other boats leaving? If we don’t go, what are the chances of us getting another opportunity in the next one/two/three weeks? ARGGHH!!! Why could the forecast not have just remained as it was?

The next step is the decision step. Lots of silence as each of contemplates the idea sailing against time, trying to get as far north as possible in the shortest possible time. It was at this point that a very salty but professional looking sailor walked into the cruising club, slamming the door behind him. With a discerning eye he surveyed the scene of three contemplative young faces transfixed on the computer screen.

“TRYING TO SAIL TO THE ISLANDS, ARE YEH?” he booms at us? Surprised at his intuition I tell our story.

“LET ME HAVE A LOOK” With a practiced air he assumed control of the laptop, jumping from webpage to webpage, clicking through each day of forecast. The day 1 (April 21st) forecast gets a “GOOD”, as do Day 2,3,4 and 5 (April 22nd, 23rd, 24th and 25th): “GOOD”, “GOOD”, “GOOD”, “GOOD” The excitement begins to mount again.

Day 6, April 26th…

“AH YEAH, WHAT’S THIS?” Mr. Salty Sailor goes quiet

Day 7, April 27th…

“HAVE YOU HAD A LOOK AT THE 500mb CONTOUR MAP?”

The 500mb contour map is an incredibly powerful forecast tool, one that we are just starting to come to grips with. Anyone that asks this question and demonstrates an understanding of the high altiture pressure map has an understanding of weather forecasting better than 99% of the people on earth.

“Well, yeah, we have the information here, but to be honest we are still learning how to use it”, I reply.

“BRING IT UP, MATE, LET’S HAVE A LOOK AT IT”

I bring it up, rotate the computer towards Mr. Salty Sailor and watch as his expression changes as he clicks through the forecast, from a blank non committal expression to a firm and knowing one.

“MATE, I HAVE BEEN A PROFESSIONAL SKIPPER IN THESE WATERS FOR 15 YEARS, I HAVE SAILED TO THESE ISLANDS PLENTY OF TIME AND I AM TELLING YOU NOW, DON’T GO MATE. I WOULDN’T GO, NO WAY. TOO RISKY. THINGS ARE UNSETTLED UP THERE, MATE, IT IS STILL TOO EARLY TO LEAVE WITH A FORECAST LIKE THIS. NO WAY YOU WANT TO TO OUTRUNNING ONE OF THOSE PUPPIES. BEST CASE SCENARIO YOU DEAL WITH A COUPLE OF DAYS OF NORTH WINDS, BUT WORST CASE COULD FIND YOU IN A FULL SURVIVAL SITUATION.”

“Err, really? You don’t think the forecast may change, this wasn’t here yesterday, maybe it wont be here for long.”

“MATE, NOT WORTH IT. WAIT. DON’T GO. TOO RISKY” He turns to leave “I GOTTA RUN, MATE, GOOD LUCK, IF YOU KNOW OF ANY OTHER BOATS LEAVING, TELL EM TO WAIT TILL THE UPPER ATMOSPHERE STABILIZES. WHEN IT IS LIKE THIS THOSE LOW’S COULD DROP DOWN ANYWHERE, AND THAT IS WHY THE FORECAST IS CHANGING SO MUCH FROM DAY TO DAY. YOU’LL GET A GOOD WINDOW SOON ENOUGH”

With those words, he closed the door and was gone. We have not seen him since, nor had we ever seen him before. With all the unknowns surrounding the decision, it was refreshing to hear a good, honest, definitive and decisive opinion from someone who clearly knows what he is talking about. Generally after turning away from a decision to go, there is always the lingering doubt that you made a bad decision, and that everything would have been fine had you left. Time will certainly tell – when April 26th rolls around and we are still tied to the Opua dock, we will either be looking at a plot of a friendly ocean north of us, OR, at the isobars of a full fledged storm. What really counts, and what you have to believe is that you made the best decision at the time, with the information available to you at the time. Never is the expression that hindsight is 20/20 more true that when judging a weather window after the fact. Even now, 24 hours after deciding not to go, the forecast has changed remarkably, for the better. Boats that decided not to go yesterday, left this morning. We did not. Who knows what tomorrow will bring? For the sake of us not second guessing ourselves, we hope that the storm does develop and justify our decision to stay put, BUT, for the sake of the other boats that did leave, I hope the weather stays clear and the winds fair. The decision to leave can only be made by each individual boat, and one must be very careful not to get sucked into the momentum of a mass departure. One may feel safe out there with lots of other boats around, but the truth of the matter is that once a storm hits, you are very very alone.

So here we are – we sit and wait, and wait and leave when all looks good! Currently, the long range forecasts are predicting a good window on 1 May. Watch this space J

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