The short answer is no. The reason is that exchange–rate movements, over the short run, are pretty much unpredictable.
Even if there are currencies out there such as the Swiss Franc that have a history of providing a safe haven in turbulent times, the exact movement of any exchange rate is best described as a Random Walk. That’s a process whereby you have just two options and you can either go up or down with equal probability – like flipping a coin. It’s effectively gambling.
There are hugely complicated models out there that try to predict or forecast exchange rates and it’s fair to say that they all do miserably. That’s over the short run – anything less than six months, say. Over the long run there are theories that would tell you what exchange rates should do. One of these is called Purchasing Power Parity.
The idea is pretty simple: if you have a comparable representative 'basket' of goods and services – something to eat, housing etc – then that basket should cost the same in all the countries if expressed in the same currency. There is some evidence that this holds over the long run but that’s really over ten years rather than six months. Currencies are interest-bearing assets (investments that pay regular interest), so nominal interest rates (the bank’s stated interest rates, not taking inflation into account) define the relative attractiveness of any two currencies. If interest on, say, dollar deposits is higher than on sterling assets, the demand for dollars will be higher, and so the pound will likely depreciate against the dollar.
"The idea is pretty simple: if you have a comparable representative 'basket' of goods and services – something to eat, housing etc – then that basket should cost the same in all the countries if expressed in the same currency."
Nominal interest rates, in turn, reflect the prevailing monetary policy in a country. That way, you can take a view on the relative monetary policy to be pursued over the near future in the US and the UK, say, and choose dollars because you think you’ll have higher returns. Even if you do, however, to make a fair comparison at the end of the period you need to convert back into pounds sterling to judge what you’ve earned relative to someone who stayed in the UK, and no one can tell you what the dollar-sterling interest rate is going to be in a year, so you run a considerable risk.
You may be lucky, but it is luck. To make it safe you would have to, at the same time as you transfer your savings into dollars, purchase a Forward Contract that would guarantee you the same exchange rate when your dollar deposit matures, and it doesn’t take a rocket scientist to tell you that the price for that Forward Contract is going to be exactly the spread between the higher US interest rate and the lower UK interest rate. There’s one iron law in economics: there’s no free lunch.