You already have HF so may not need to spend or install anything at this point in time. B.o.M has a HF SSB marine weather service which covers all of Australia.

http://www.bom.gov.au/marine/marine_weather_radio.shtml

In NZ contact
www.maritimenz.govt.nz/Recreational-Boating/Marine-weather-forecasts.asp

Between the two of these you should have more than adequate coverage, providing your radio and antenna is up to it.

Rick,

I have Icom 710 HF (SSB) and "Weatherfax" app on my Ipad and Iphone.

Tune into appropriate HF frequency and the app interperets the signal and draws current weather map.

The forecasts are available at regular intervals on HF also.

I used this method on my trip to Lord Howe Island and it works great.

I have a backstay HF antenna with Auto Tuner

Steve

www.sweetchariot.blog.com

I am presently sitting in front of the boat computer downloading routing and weather gribs for a Tasman crossing from Opua NZ to Eden ETD Thursday or Friday.
Perhaps your question on weather technology might be putting the cart before the horse as you will need to have your boat set up to Category 1 offshore safety regs prior to departure as there is not much point knowing you are in for a hiding if you aren't set up to deal with it if things go pear shaped.

However to weather.Get a subscription to a weather forecasting/routing service. I use PredictWind but there are others and there is a NZ weather guru Bob McDavitt who is well worth looking up on the net.
PredictWind is presently telling me my departure on 28-2-13 will take 6 days 16 hrs and 54 mins covering 1207Nm 96% time reaching 4% running. 80% wind 8-20knots 20% wind 20-30 knots. Play around with these internet based services and see what you are happy with.
Then there is the boat comms and onboard software. I run a mini AT machine as boatcomputer with Expedition, Maxsea and PC Plotter for navigation and routing software, and of course a laptop for backup. Contact with the world is maintained via Inmarsat Fleetbroadband using a Skipper 150 satellite reciever for broadband and voice contact. I don't have an HF radio but they do tell me that it is possible to send email using a Pactor modem coupled to your HF although it is probably quicker and easier to send a morse code message.
What I would recommend for a one off crossing is to purchase (you may also hire) a handheld satphone. I use an InmarsatPro with prepaid airtime. This phone for me is packed in the grabbag with the EPIRB because if I have to step into a liferaft then the non existent HF and the Skipper150 unit are no longer operational. Preprogram AMSA +61262306811 in the phone and let them know you have set off the EPIRB and would like assistance.
Would also buy a SPOT tracker with a tracking subscription. This sends out your GPS coordinates to a Google Earth server by satellite every 1/2 hour. Your friends and family can follow your track in real time on GE.
Your navigator and route planner then does not actually have to be on board. They can spend hours on the internet watching the weather forecasts for you and you can phone them for detailed weather at prepaid airtime rates of approx 60c per min.
It is also possible to use a handheld sat phone as a modem for emails.
MOST importantly however keep your watch on the barometer and your weather eye open because the weather doesn't read the weather forecast.
Try GreatCircle for liferaft, EPIRB, PLB and sat phone hire.
Good luck with the passage.

NZ customs will only prevent a New Zealand flagged vessel from sailing if the boat doesnt satisfy Cat 1 safety regs. All entries to offshore racing must satisfy the appropriate category for entry to be accepted. Most cruising rallies will stipulate a requirement to satisfy Cat 1. If cruising on your own we hope that there is no big brother stipulating that you MUST do this, however it would be prudent to check your safety equipment against an established standard prior to sailing. It is your life after all.