Forex expert Douglas Borthwick and panelist on TheStreet's latest Trading Strategies roundtable said the weak dollar is the basis for September's market highs as Wall Street leaves the summer behind. "I think the dollar is the basis for everything," Borthwick said.

Borthwick said that as the dollar weakens by one percent, the S&P earnings move up by half a percent. "As long as you see the weakening dollar, I think you'll continue to see the market go up," Borthwick said. 

In addition, Borthwick said that people may be feeling a little more confident as fears of a North Korean nuclear strike ease and Hurricane Irma has passed and the rebuilding is widely seen as a positive for the economy. "These things will have the market take a sort of pause right now that refreshes." 

Borthwick said that if the dollar remains weak among these events, it will continue to move up.

Check out more of our September Trading Strategies special report below: