… And Talk About the Weather

Every end of season we take a closer look at the weather. Last year, it was the risk of a hurricane hitting us in French Polynesia. This year, it’s all about the weather for the passage to New Zealand.

So I thought I would dedicate a post to share how we are looking at it.

But, for the sake of disclosure: this is a nerdy post.

And before we get started:

• This is not intended to show off any weather prowess on our part
• This is how WE are looking at the passage for OURSELVES and should not be taken as advice by anyone else
• That said, we thought it might be of interest to share the sources we are using and how we are looking into it.

Ok, now on to it.

As mentioned before, the weather along this passage has a few distinct characteristics:

• it can be rough, particularly on the second half and the approach to NZ
• in general, it follows a structured pattern, one which is well monitored and forecasted for

After talking about it, we have decided that we wanted this passage to be a good closure to this cruising season and also to our cruise of the Pacific Ocean. With that in mid, we selected the following criteria for it:

• no tight upwind sailing. No deep/dead downwind either
• sustained winds of no more than 25 knots
• waves no more than 3-3.5 meters high
• minimal motoring
• strong preference for riding one single High all the way to NZ
• no departure if a Low is forecast to be in the sector

Over the last months we have been gathering anecdotal information about the passage, tips, and sources of info. More recently I have also resourced to a bit more technical information to gain some basic understanding of fundamentals of the weather patterns on the region. Finally, we are proactively seeking information from local weather experts. In the end, these are the resources we have used or are using on a routinely basis:

• Gulf Harbor Radio: a thorough source of information. I found this article particularly educational. David and Patricia also host a daily weather analysis and roll call over the Broad Side Band Radio.
• MetBob: the local “weather guru”. Bob has thorough understanding of all-things-weather in the Pacific. His weekly Weathergrams normally give an excellent Big Picture view of the macro region around us, in addition to tips about cool sources of weather info. We have also engaged him to provide us with specific advice for our passage.
• “Bad Weather Avoidance […]” book from Ma-Li and Lee Chesneau … boy, it’s an arid read. But it does offer practical and actionable tips to understand forecasting fundamentals and improve long-term-planning.
• GRIB Files downloaded daily, containing: 500mb (Geopotential Height), Surface Pressure, Winds and Rain. The GFS model is still our main trusted source of forecasting, and we get it from Saildocs. We also look a lot at the ECWMF, via WindyTy (the latter has proven extremely good for micro, short term forecasting here in Fiji). Recently we have broadened our access to two new models by using the Predict Wind services.

We have now established ourselves on a daily routine to monitor the weather which consists of :

• daily monitoring of macro conditions using a large-scale, low-resolution, 14-day forecast from the GFS Model. That’s where we look for the desired (and undesirable) patterns for the passage. This monitoring is complemented by:
  • a weekly weather analysis from the local weather guru – MetBob
  • occasional listening to Gulf Harbor Radio
• daily monitoring of windy.com, where we look for consistency (or otherwise) with the GFS, as well as local weather trends here in Fiji
• If something gets our attention – be it from the regular monitoring above, “heard on the streets”, or a note from our weather consultant – we zoom in on our analysis:
  • downloading a high-resolution GFS file and looking at windy.com profusely
  • cross-checking with the other two models of Predict Wind
  • eventually enquiring directly with MetBob

Here is how it has been happening in real life.

*** WRITTEN NOV. 7th ***

A patter of a benign High Pressure system recently passed under us. It offered excellent passage conditions for over a week, but it happened when we were still not ready, and too early for us to go anyway. Now, it has been replaced by a pattern of unstable conditions, mostly characterized by Low Pressure Systems, which can deliver bad weather.

That being said, there have been talks of a potential window, with possible departures this week, starting yesterday Nov 6th. Some boats are preparing to leave, and even MetBob has asked if we were intent to go. So here is what we see:

A passage would be seemingly feasible – here a view of winds at the middle of the trip …

 

… at a closer look though, it would be close-hauled sailing for a good part of the trip, with apparent sustained winds of up to 25 knots. Way too intense for us …

 

… worse yet, Forecasting Models are not agreeing much along the period, hinting to a lower prediction confidence for any of them …

 

… adding to that, we would be arriving to NZ just ahead of a nasty-looking Low Pressure system that is forecast to spawn at our tail at the middle of the journey. With the low confidence of the scenarios mentioned above, that thing could in practice outpace us, creating very uncomfortable conditions. Moreover, we would have absolutely no cushion, and be hard pressed to reach race to NZ ahead of it …

 

So, while doable, this is not the type of passage we are interested in doing. We still have time available, and prefer to use it in waiting for a more benign pattern.

And it’s not just blind fate that we have. My longest-term forecast, a GRIB file from the GFS, is showing the possibility of an Upper Level Ridge approaching our sector. These patterns in the upper atmosphere normally create conditions for benign weather – in our case a High Pressure System on the surface of the ocean. I know it is far-fetched and just a faint possibility at this time. But I trust the GFS, and my guts are telling me it’s going to work:

 

*** WRITTEN NOV. 13th ***

There have been new talks of a possible window later this week, with departures on Wednesday or Thursday (Nov 15th, 16th). Some boats will be leaving, and again MetBob has asked of our interest. Let’s see:

Wind conditions do seem “right” upon departure on the 16th, but notice how a Low is forecast to form to the west of the course midway through. We wouldn’t be at the “punch” side of it, but still it’s a Low. And we would be motoring for most of the way …

… moreover, being a Low, there could be rain, lots of it …

… and all those winds around us would generate waves. While the models don’t agree – bad in itself – I do trust GFS. And the GFS is saying 4.5 meter waves on the approach to NZ  …

Lows, Big Waves, Rain, Motoring … most of our core criteria being broken. Not what we are looking for.

We understand that the longer we wait, the higher the possibility of a Cyclone forming in this region – the Season has officially started already. However, my guts are still saying that we will be able to ride one benign High pressure system all the way.

And there is good news. The Upper Level forecast we saw a week ago is materializing, and there seems to be a good High Pressure system approaching from the West next week. This is still a far-fetched forecast, but that’s where I am placing my bets right now:

 

To that matter, we have already booked a space at Denarau starting on Friday (Nov 17th), where we will do our final preparations, take our last provisions, and be ready to check out of Fiji.

That’s what I have for now, folks. I will keep the blog updated as our decision-making progress this week.

Stay tuned, and THANK YOU for following our Journey !

*** UPDATE NOV. 14th ***

A few movements have been testing our assessment and decision. News arrived that a Trough (weather system) might arrive to NZ on Nov 25th bringing unstable weather. As a consequence, it might be better for us to anticipate our departure, ideally to Friday, Nov 17th …. hmmm.

Since the news came from a trusted source, it attracted my attention. A quick look at the GFS accompanied by a simulation on Predict Wind showed that a departure on Nov 17th would be far from our desired passage criteria:

• a big Low would still be present in the sector by the time of departure
• light winds would cause us to motor for at least three days, if not more
• there would be at least two days of hard-on-the-wind sailing

Not ideal. So the attention shifted to the potential Trough. Indeed, a look at Windy.com shows a Trough forming between two Lows right under Australia on Nov 23rd (the furthest I can get on Windy.com today):

 

Those two Troughs will me moving East and two things can happen:

• they can displace the Highs above NZ, bringing unsettled weather to the region and affecting us underway or,
• they can slid to the South of the Highs, not affecting our region of interest

So we look at how the Upper Atmosphere will be looking like by then. These are the steering conditions for surface weather:

 

That Upper Level Ridge reinforces the conditions of the two Highs on the surface. So my bet is that the Highs will prevail and push the Troughs to the South.

As of now, we are still betting on a departure next week, and a stable and enjoyable ride to NZ !!!

 

*** UPDATE NOV. 17th ***

Yesterday evening we had a jumpscare. After dinner I checked the weather one more time, downloaded a long-term GFS forecast from Saildocs, and was horrified with the result. A series of Lows forecast to spawn along our path to NZ, right during the time we were planing to do it. Lows that didn’t show up on previous forecasts. In a way, it seemed like our weather window had crumbled.

Fortunately it was a one-time event with the model, a certain type of fluctuation on the long-term forecast which can happen from time to time. Today I ran a few more forecasts, and all new versions of it are showing our beautiful, unobstructed weather window again.

 

We are good to go.