There is an Analysis paralysis at Tongatapu with lots of weather data and discussion but little decision as to when may be the best day to depart for NZ.
Here is some more information , just to show that different yachts may have different optimal solutions.
First this is an ensemble of computed optimal paths from Tongatapu to Opua starting noon on Sun 28 Oct and noon each day after that to Sat 3 Nov. There isn’t really enough data to get all the voyages after 1 Nov to Opua.
Ensemble paths computed by Expedition software http://www.tasmanbaynav.co.nz/
Here are the details comparing the different departure dates from Tongatapu to Opua:
Departing on Sunday will result in encountering the S and SW winds that are on the western side of a LOW moving NE off northern NZ on Sun/Mon 28/29 Oct.
The isobar Map is the GFS model for Sat 3 Nov showing a Low in North Tasman that is expected to travel SE across the North Island – the NE winds on its eastern side ARE useful for the voyage to NZ .
Just to show you the variety amongst the models here’s the ECMWF for 12Z on 3 Nov—it has the Low further north and not much wind between Tonga and NZ, at least it is a northerly:
That trough which passed over Tonga last Friday/Saturday is followed by a large slack area on the weather map. So there are light southerly then variable winds at Tongatapu this week with a sailing breeze returning around 3 Nov.
Spot GFS data for Tongatapu this week from Expedition
This means that those who wish to sail to NZ and save on motoring should stay at Tongatapu this week .
Those with deadline and wanting to get to NZ as soon as possible can motor off around Monday Tuesday or Wednesday and hopefully capture the northerly flow that may be on eastern side of that Low from Sat 3 Nov. This is an idea from the GFS isobar land at present,but has a good chance of working .
the best day to depart depends on you boat speed , slower boats on Monday and faster boats on Tuesday /Wednesday.
Then there are those yachts who may want to check out Minerva. Ideally to do this you need permission from Fiji authorities .
Minerva is also having a week of light winds :
And a sailing breeze is expected to get back there around 3 Nov , just as in Tongatapu.
So motoring via Minerva and stopping off there IS an option—it gets you 1.5 days closer to NZ once the sailing breeze returns, but will cost in motoring fuel. If you stop the it also means that you’ll miss the opportunity being offered by the northerly winds on the eastern side of the expected 3 Nov Low… then again that Low is not yet definite .
Those wanting to sail the whole way: wait until at least 3 Nov
Those wanting to visit Minerva : motor off when you like.
Those wanting to get to NZ straight away : Motor off on Monday if a slow boat ,or on Tuesday or Wednesday if a faster boat.
Hope this helps