The weather in Lianjiang in the coming week

A, the probability of rain tomorrow is 70%, which means that it is more likely to rain tomorrow, rather than 70% of the area will rain tomorrow, so this option is wrong;

B, the probability of rain tomorrow is 70%, indicating that it is likely to rain tomorrow, so going out without an umbrella tomorrow is likely to get wet, so this option is correct;

C, the probability of rain tomorrow is 70%, and I didn't say it will rain tomorrow, so going out without an umbrella tomorrow will definitely get wet, so this option is wrong;

D, the probability of rain tomorrow is 70%, which means that it is more likely to rain tomorrow, rather than 70% of the time, so this option is wrong.

So choose B.