Another month, another set of grim sales figures from the Rhode Island Association of Realtors.

There were 548 single-family homes sold in Rhode Island last month, the Realtors reported this morning. That’s a drop of 29% from last August, when 768 homes were sold shortly before the original Sept. 30 expiration date of the federal homebuyer tax credit. It follows the record 34% plunge in sales we saw in July.

If you’ve been reading Nesi’s Notes, you won’t be surprised by today’s numbers, dismal as they are. Pending sales – an indicator of how many transactions are in the pipeline – have been falling since March.

The state of the housing market is vital to the broader health of Rhode Island’s economy, and with unemployment still in double-digits, this isn’t a good sign. Vince Valvo, group publisher at The Warren Group, told me in an e-mail that he expects this trend to continue through the first half of 2011:

We’re going to see big drops in sales numbers probably every month through next June. That’s right – for almost another year.

Pending home sales have been down every month since the tax credit expired. That means that the number of homes that close a couple of months later can’t be anything but down, too. So right now, the math doesn’t support any scenario where home sales at least through December can be up from last year. You can’t sell more houses than you’ve got contracts for.

Once we get into next year, we’re going to be comparing sales against the artificially-inflated numbers that we got because of the tax credit. Remember those big gains that got reported right through June of this year? Well, there’s no way next year’s first half is going to be that robust. So every report at least through June of 2011 is going to show housing sales dropping.

This isn’t a question of hope, or wishful thinking, or doomsaying. It’s math, pure and simple.