It will be warm and humid but not much more than Sydney at that time of year. Why not leave it until you are here as there will be plenty of places available and it can be a wonderful time of year to visit if the weather is kind to you.

Here is the climate data for mean monthly maximum. http://www.bom.gov.au/jsp/ncc/cdio/weatherData/av?p_nccObsCode=36&p_display_type=dataFile&p_startYear=&p_c=&p_stn_num=031011

Unless you plan on getting well out of the city, I don't think you'd need "several days" in Sydney - two or three would be fine, in my opinion. On the other hand, there's much more besides the Barrier Reef to see in the Cairns area (North Queensland) - definitely worth spending more than just a day or two.

The Great Barrier Reef is a World Heritage Site and well worth a visit, no matter the time of year. I have snorkeled in a lot of places around the world, but this has been, hands-down, the best I have ever experienced. Unless you know that you will be returning soon to this area during a less humid time of year, then I would not pass up this opportunity to go.

In addition, this area is the home to another World Heritage Site, the Wet Tropics of Queensland (e.g. Daintree National Park). As Ralph points out, there is more to see in Far North Queensland than just the Reef. I agree with him that 2-3 days in Sydney proper should be sufficient and you should plan on at least 3 - 4 days in the GBR area.

Thank you all for your advise! We have decided you are absolutely right and we are going to give it go! Two days in Sydney then off to Cairns to experience the GBR. Any recommendations for a small group charter with a friendly, knowledgable crew and captain, for a day trip. We'll also look into a tour for the Daintree National Park. I guess we'll need at least a day for that as well.

I can highly recommend Wavelength that operates out of Port Douglas (which is where I'd recommend you stay anyway). It is a snorkel-only boat which carries a maximum of 35 passengers. You will read great reviews about them on threads here or on Trip Advisor. There is a marine biologist on all trips to inform you about what you will see underwater. In fact, at the 2nd stop, the biologist will do a guided tour which you are welcome to join (not required) and bring up interesting things to show the group.

I have gone out with Wavelength on 5 different occasions and they were excellent each time.

Longhorn55 - Can you tell me a little more as to why you recommend staying in Port Douglas over Cairns. We do not plan to rent a car, how far is it from the airport?

These are the two main reasons I like staying in PD:

#1 (and this is a big #1 for me): PD has a beach (Four Mile Beach) and Cairns does not have a beach. There are beaches in the northern suburbs of Cairns, but not in the city itself. Even though swimming at the beach in March is restricted to the areas protected by a stinger net, it's still great just to walk along Four Mile Beach or sit on the beach and look at the water.

#2: PD is a small town (population just over 3000) and Cairns has a population of over 100,000. I like the small town feel of PD and being able to walk from my hotel to the beach or into town.

PD is about 65 - 70 miles north of Cairns. There are coaches that will take you from Cairns Airport to PD. I have used Sun Palm Transport, but there are other options as well.

PD is pretty quiet, so if you are looking for more in the way of shopping and/or nightlife, then Cairns would be a better choice for you.

In addition to Port Douglas, the other place to look at is Palm Cove, which is north of the airport but not as far as Port Douglas (20/25 minutes to Palm Cove, maybe an hour to Port Douglas). Almost anywhere you stay in Palm Cove or Port Douglas will be able to arrange transportation for you from/to the airport. They will also be able to arrange any trip to the reef etc, including pick-up/drop-off from wherever you're staying.

Other places to visit in the area include the Atherton Tablelands. Many people also do the Kuranda trip - take the train up and the skyrail back. Again, your accommodation will be able to arrange it for you.

Palm Cove - the video (scroll down) on this site will give you some idea of what to expect - http://www.palmcoveaustralia.com

Kuranda - http://www.kuranda.org
http://www.ksr.com.au
http://www.skyrail.com.au

More than that now Longhorn, residential population as at June 2011 around 170,00 but that includes Douglas Shire (Port Douglas) which has been part of Cairns Regional Council since council amalgamation in 2008.

It is true that Cairns city does not have a natural beach, (it does have a large stinger and croc free waterfront lagoon) these start a little north of the city and include Palm Cove mentioned above. It is also true that Cairns city is a regional Queensland city, not just a tourist town, so expect to come across public infrastructure such as hospitals, government offices and various businesses you'd associate with a small mainly residential city.

But more reef boats leave from Cairns city than from Port Douglas (usually at less cost) - yes there are transfers from beaches etc but they cost, so staying within walking distance of Cairns Marlin Marina can save quite a bit in transfer fees. A good small reef trip out of Cairns is Sea Star - www.seastarcruises.com.au

Skyrail out of Cairns has just recently included a brand new Djabugay Aboriginal Guided walk which is getting rave reviews: www.skyrail.com.au/tours.djabugay-return