It’s been a sleepy year so far in the Manhattan office-leasing world, which is to be expected. Vacancy rates are at a huge low and average rents are at an all-time high.

But brokers are quietly saying it’s going to be a very busy summer and, indeed, things are picking up. Take midtown recently: In April, leasing activity there nearly tripled what it was in March, according to stats from brokerage CB Richard Ellis; companies leased 1.84 million square feet of office space versus 660,000 square feet in March.

In Manhattan overall, April hosted 2.63 million square feet of office leases, and, in March, 1.42 million. The Manhattan vacancy rate fell during April to 4.5 percent.

The month’s biggest lease was the 415,000-square-foot Lehman Brothers deal finally closing at 1271 Avenue of the Americas.