Tech stocks were on fire in August. The Nasdaq composite gained 5.7 percent, making it the best August since 2000, but not all experts are sure September can maintain the pace.
"In this environment where we're in, where things really look good coming out of August, I think you've got to keep your eye out on what could go wrong. A good sailor looks at the horizon and says where is the storm cloud brewing. I'm just saying I've got my eye on it," Jim Lebenthal, partner at HPM Partners told CNBC.