It's unbearable when it's cold like this.
It is possible to use てかなわない、as in 寒くてかなわない. The difference between them is like the difference between て (It's unbearable because it is cold) and ては (It's unbearable when it is cold like this). The て is not used with こう and こんなに as often as ては. The latter also has a stronger nuance of displeasure.