SANTA MONICA, California — Nissan is preparing a new addition for its popular Murano crossover lineup, and surprisingly enough, the future SUV will be a convertible.

On the market since 2003, the five-passenger SUV underwent a complete makeover for 2009, and now Nissan is engineering a drop-top version of the latest-generation Murano. Expected to arrive by the spring of 2010, the Murano drop top will be the market's only four-door convertible except for the Jeep Wrangler Unlimited, whose rugged four-wheel-drive capability is geared toward a completely different audience.

Insider sources close to the project say the 2011 Murano convertible will be produced in limited numbers, and will be targeted at empty-nesters who need room to carry the grandkids, but still want something fun. But the kids will need to pack light, as the current Murano offers just 31.6 cubic feet of cargo capacity, and the convertible mechanism will certainly cut into that space.

Although retractable hardtops are gaining in popularity, the Murano will stick with a more traditional soft top to keep weight down. Less heft should help keep fuel economy similar to the Murano's current 21 mpg combined city/highway rating, as the 265-horsepower 3.5-liter V6 and a continuously variable transmission (CVT) used in the 2009 Murano is expected to remain. We also expect front- or all-wheel drive to be available.

Don't expect the 2011 Murano convertible to come cheap. A top-of-the-line 2009 Murano LE with all-wheel drive and an optional navigation system is priced at $39,080 including delivery charges, and the new convertible model will likely sit at the top of the lineup.