When your interest raise, your currency will be more attrative, demand for your currency increase, given floating ex-rate, price of yr currency raise, i.e. Appreciation against other currency.

Besides, as the boom of financial market, capital inflow, which is equalivent to a raise in demand for your currency, also may lead to the same result.

under floating ex-rate, the BOP is always in balance because the ex-rate will adjust for any excess demand and supply for the currency.

however,if there is linked/fixed ex-rate, BOP surplus means that the currency is under-valued, which may impose a upward pressure of the currency price.