Cyclone season is the time of year cruisers must be the most vigilant.  It is not safe to sail around in zones that are prone to having cyclones, hurricanes or typhoons.  So, what do we do?  There are many decisions to make depending on where you are in the world.  We are currently cruising in the South Pacific. Pretty much any place in the tropical zone, 10 to 30 degrees off the equator, can be a place that has cyclones.  Each year we must plan where we need to be November through the following May and work our cruising plan backwards from there. Here is how we came to choosing to stay in Vava’u Tonga for cyclone season.

Cyclone Seaon in the Southern Hemisphere

Cyclone Season lasts from November to the following May in the southern hemisphere.  It is exactly the opposite of hurricane season in the northern hemisphere, the danger to boats remains the same.  The conditions are also the same.  The water temperature must be at least 80F at the surface and down to about 150ft.  Of course you need a low pressure system around sea level.  Then there are some other factors like vertical wind shear, thunderstorms and continuous source of warm moist air.  With this knowledge one atmospheric event that I follow very closely is the location and strength of the Madden-Julian Oscillation (MJO).

The Madden-Julian Oscillation

The Madden-Julian Oscillation is a large scale disturbance.  It is a wave of energy that drives many of the factors that can produce a cyclone.  In fact, I have read that in nearly all case in French Polynesia the MJO was present during cyclones.  This system rotates the earth around the equator, every 30-60 days.  It drives warms moist air and produces violent thunderstorms and powerful low-pressure systems.  I use this DTN website to see the actual local of the MJO and the forecast for the next several weeks.  In particular I like this view as I can follow both the active and inactive regions and see the strength of the active phase.  The darker the green the strong the activity.  So with all that said how did we decide to stay on Vava’u Tonga for Cyclone season?

Challenging the history

I did an analysis of the historical weather as well as what is available in Vava’u in terms of moorings, haul out facilities, etc.  First the weather.  I am a big user of Open CPN.  In fact after our last lightning strike we use Open CPN is our primary navigation system.  One of the plug-ins offered in Open CPN is climatology.  The plugin allows you to overlay various types of weather data of a specific place on the chart for a given period of time.  In this case, I wanted to see cyclones.  Here is what the cyclone tracks look like overlayed around Vava’u Tonga, without any filters.

I know what you are thinking, geez each of those lines are cyclones, are you crazy?  Well yes they are and the date range is from 1949 to present.  You might note that Vava’u seems to be in a bit of a pocket and if I filter on only La Nina – the map changes dramatically.  See below

There is one very important data point to understand about cyclones in the Southern Hemisphere, they name their storms at very low wind speeds – 34KN.  It is not until you reach CAT 3 here that the wind speeds match a CAT 1 in the US.  On this map, the light blue is 40kn and the green is 60.  Not even CAT 1.  If you remember, Tami and I sat through more than 60KN of wind at anchor in French Poly last year.  Does this mean there will not be a cyclone, NO!  What it means is in a La Nina year there are very few.  This is more than 70 years of data.  You can also see there are many more in Fiji and also a few red lines, more than 100KN of wind – not cool.  But more goes into it.

Local facilities

Here in Vava’u they have good facilities in the event we need to use them.  First, the Boat Yard Vava’u can haul our boat out if we choose to.  They have a way to secure the boat to the ground and we would take shelter in a local hotel or something like that.  They also offer hurricane safe moorings.  I have personally spoken to people that have been on the mooring in high winds, and they are more concerned about something hitting them that got loose in the harbor then they were about the mooring breaking.  The service these mooring often and in my view, they are well maintained.  As of this writing there are only a view boats that have selected to stay here, so I have no competition for moorings our being hauled out.  Whereas in Fiji, the yards are full, people pay to get a spot in the mangroves all of course based on availability and there are hundreds of boats – hundreds.

The final factor, for cyclone season, is Sissy!  She can not be imported into Fiji. New Zealand is possible but would cost thousands of dollars.  Our Sissy girl is getting old, 14 years now, and a rough sail south might not be very good for her health.  Here in Tonga, she is imported and is free to go wherever we go on land.  The dogs are not too aggressive, so it works very well.  Another small factor is the locals speak English, so it makes you stay comfortable and our chances of participating in local festivals and activities increase. 

Staying in Vava’u – Simply Amazing

In the end, I do expect we will see some weather.  How strong, who knows.  We have more than 30 beautiful anchorages we can explore, with one eye on the MJO.  However, these anchorages are all within 20 miles of the main harbor.  This harbor found in 1781 by Spanish explorer Francisco Mourelle de la Rua.  He named it Puerto de Refugio – The Port of Refuge.  We have this paradise all to ourselves with a port sailors have used for safe harbor for more tahn 200 years.

One final note, I am not a prefessional meteorligist. I am sailor that analysis what is avaialbe to me to make the safest decision for our vessel.