Should I rethink my portfolio allocation now since Yellen is increasingly likely to raise rates later this year?

A lot of that depends on what your current allocation is, what allocation you are considering moving towards, and what your goals are for the money you are talking about. We are sort of in a catch-22 of sorts.
With a high likelihood that interest rates will start increasing in the next 6-12 months, it is probably not the best time to move a sizable portion of one's portfolio to fixed income, unless you are going to focus on short term fixed income, which would be impacted a bit less by increasing interest rates than longer-term fixed income. Since the likelihood is high that interest rates will probably start increasing in the relatively near future, that means it is almost a certainty that the price of existing bonds will decline.
On the flip side, the markets as a whole, and some individual stocks are at, or near, all time highs. Some would assume, and argue, that this means there is nowhere to go but down. If you subscribe to that philosophy, then moving a chunk from fixed income (which is almost certain to decline at least somewhat price-wise in the next 6-12 months) to equities probably does not sound appealing.
However, if you believe that there is no way to know what will happen in the equity markets in the short-term (i.e. prices might go down from here, but they might continue going up for an extended period as well) and that at some point in time now and over the next 30 or 40 years, equities will continually reach new, higher "all-time highs", then it may be much more palatable to move money from fixed income into equities at the moment.
There is no right or wrong answer to your question since we don't know what your current allocation is, what your short and long-term goals are, etc.
If you have a long-term time horizon (say 5, 10, 20+ years), then moving out of fixed income into equities right now is probably fine. Even if the equity markets took a short-term hit, their long-term prospect is still excellent, especially when compared to fixed income.
If you are thinking more about moving more of your portfolio to fixed income, now is probably not the best time unless you are talking about target short-term fixed income instruments.
Hope this helps some and best of luck.

There are two contrarian approaches you can take: assume that the Fed won't be able to raise rates when they want to as that is what everyone is expecting/waiting for them to do or you can look at several ETF's that will profit from a rate increase (AGND/HYND) or use ETF's that may provide some income, but invest in short term debt (FISM/GSY/NEAR). For the truly aggressive who can hover over a quote provider all day, you can look at leveraged bear market ETF's. Those should ONLY be used as day trading vehicles.

You could also use the options market to sell covered calls against portfolio holdings or buy protective puts for securities you currently own. Now comes the real heresy. You could find an advisor to work with who has the time and knowledge to help you with your concerns and pay them for their expertise. There is a vast base of data that shows that most individuals on their own have a very poor feel for when to be in and when to be out of the market. Going it alone has its costs.

One other problem most of the contributors here have is an industry rule we all work under: Know Your Customer. We have very little personal information to go on to make a "do this" or "do that" recommendation for a specific market scenario. Your definition of risk is probably very different than mine, so my (our) solutions may not be applicable to your goals and risk tolerance.

I don't always follow the Efficient Markets Hypothesis (which states that all available information is currently priced into a given investment or market), but in this case I do think it is. In other words, the eventual rate hike has been expected for years now and I feel that  this expectation has already priced itself into the intrinsic value of interest rate sensitive holdings. 
It's hard to say if you should adjust your allocation without further knowledge of your portfolio and the purpose/timeline for your investments. If your primary hedge against equity market risk has been interest-rate-sensitive fixed income, then I'd suggest looking into some alternative forms of mitigating systematic equity market risk. Many advisers on this site, including myself, would be happy to provide you with some complimentary insight.  
-Adam Hardingwww.linkedin/in/adamharding
Not to be considered investment advice. For informational purposes only.