I havent windsurfed over east but Ive done alot of surfing.
Theres no surf in the town of 1770. There is some sort of fat rolling wave that breaks through Bustard Bay south of the lighthouse. But this is a massive headland and the wind could be very gusty in there?
As for surf Agnes Waters is the only and the last surf break on the east coast.
Call Wayne from the Surf Riders. He will have all the wind, tide and wave details.
There also is a monster offshore break if you have access to boat and a local. A very heavy and intense right hander called Cookies. Would be sick to windsurf on a SE. Dont bother looking for it yourself as its near impossible to find. I almost drowned at sea trying to find it for the second trip out there. I should have dropped bread crumbs the first time

Wreck Rock between Bundy and Agnes is the place to wave sail in a SE'ly. Apparently it can get up to mast high but I've only ever seen it quite small. The beaches there already get sheltered by the reef so the swell is smaller than on the Sunshine Coast.

The season & wind is pretty much the same as Gold Coast / Sunshine Coast. There's usually not that much difference in the forecast between St. Lawrence to Hervey Bay and Sandy Cape to Coolangatta. Sometimes there's a bit more wind up there, sometimes there's more further south.

Like Greenroom said, there isn't any good surf at 1770 itself. I don't know if one can sail the river mouth in a northerly just north of the big headland (Round Hill Head I think) ? Some small waves roll in there over the sandbars. Have also watched some descent size fins cruise past from the headland and beach. Good mud crabs in the estuary though!

I've tried to sail at Agnes Water just south of the town (I think the beach is called The Springs). Waves were tiny and there wasn't much wind, not helped by a bit of a wind shadow from a small headland. Agnes never struck me as a great place to sail, although I haven't seen it in a honking SE'ly and a descent swell. Also haven't been there for 10 years, so memory a bit sketchy.

Holgs

Greenroom, the breaks on the reef look most impressive.
www.reef2beachsurf.com/reefsurfing.htm

sailed the bar off round hill head on a northeaster about 25 years ago and it was ok. launch off the rocks can be a bit dodgy but if you have someone with you just downwind back to the township afterwards. wreck rock can be good, i've had it at about half mast, the gladstone guys used to sail it alot. the beach near eurimbula creek also probably ok from nw round to east