What does Mr. White mean by, "I should hardly think that he'd come tonight"?

Mr. White says, "I should hardly think that he'd come to-night" mainly because of the bad weather conditions outside. A bit later he describes those conditions to his son and his wife:

Of all the beastly, slushy, out-of-the-way places to live in, this is the worst. Pathway's a bog, and the road's a torrent.

They are expecting a visit from Sergeant-Major Morris, but Mr. White doubts he will come on such a stormy night. At the same time, he is talking to distract his son Herbert. The two men are playing chess and the father sees that he made a bad move and gave Herbert a chance to checkmate him. A moment earlier, Mr. White called attention to the sounds of the storm outside in order to distract his son.

"Hark at the wind," said Mr. White, who, having seen a fatal mistake after it was too late, was amiably desirous of preventing his son from seeing it.

The author of "The Monkey's Paw," W. W. Jacobs, was also using Mr. White's comments on the weather in order to create an ominous mood and to apprise the reader of the dark, isolated setting of this little house. The small family of father, mother, and grown son seem snug inside, with the fireplace spreading warmth and cheer. This will come to an end when Sergeant-Major Morris sells Mr. White the monkey's paw.
In Part III of the story, when there is that terrible knocking at the door, it will seem unlikely that it could be anybody out there but the mangled and partly decayed Herbert returned from the grave. Who else would have come at night to that isolated setting in such bad weather?