NEW YORK (TheStreet) -- After a strong start to the week, stocks are roughly flat on Tuesday, as investors look for more clarity on a potential Greek debt deal. 

Financial stocks continue to trade well, especially with renewed discussions of a possible interest rate hike coming in September. On CNBC's "Fast Money Halftime Report," Pete Najarian, co-founder of and, pointed out that JP Morgan (JPM) - Get Report and Goldman Sachs (GS) - Get Report are both leading the way, and he expects the sector to continue trading higher. 

He also said investors will be able to handle an interest rate increase from the Federal Reserve

Jim Lebenthal, president of Lebenthal Asset Management, previously had expected a rate hike to come in September, but he now believes it's more likely to happen in December. Jon Najarian agreed. 

Najarian, co-founder of and, added that Greek debt issues could again be at the forefront of investors' discussions come September, making it an unattractive time for the Fed to consider raising rates.

But that doesn't concern Paul Richards, head of FX, rates and credit distribution at UBS North America. Assuming U.S. economic data remains strong, Richards said, the Fed will likely hike rates twice this year - once in October and once in December. 

He also made the case that Greece will get the debt deal it needs by Sunday, and it will not likely be an issue again until 2016. Germany wants Greece to stay in the eurozone in order to keep downward pressure on the euro. The dollar is likely to go higher, he added. 

"I'll believe it when I see it," Lebenthal said regarding a Greek debt deal. 

Stephanie Link, managing director and equity portfolio manager for the TIAA-CREF organization, looked at some of the recent economic data. She noted that the European PMI data was strong, while the May U.S. housing starts show a "clear recovery" in this market. 

The conversation turned to airline stocks, after analysts at Morgan Stanley released a bullish report. Specifically, the analysts rated Delta Air Lines (DAL) - Get Report, Alaska Air Group (ALK) - Get Report, Spirit Airlines (SAVE) - Get Report, and United Continental Holdings (UAL) - Get Report with overweight ratings. 

The price targets suggest analysts see relatively high upside too, Pete Najarian added. These airlines have earnings power and the ability to expand margins and cash flow, he said, and predicted that they're likely to do well in their upcoming earnings results. 

It's tough to own the airlines, even when they're doing well, Lebenthal said. The customers, management and regulators always seem to "hate" the shareholders, he said, adding that the stocks can be volatile. 

In 2014, investors could have owned almost any airline stock and enjoyed strong returns, Link said, but now, investors need to be more specific even though most of the stocks have low valuations. She recommends investors look for airlines with strong management teams, good flight routes and strong pricing power. She likes Delta and United as long-term investments. 

Jon Najarian touched quickly on Ambarella (AMBA) - Get Report. He bought the stock on Monday's big selloff, and because shares have bounced back so quickly -- rising about 7.6% on Tuesday -- he sold 75% of his position. He also likes GoPro (GPRO) - Get Report stock.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.