Taking shelter from rain | Golf Monthly

There is no 'reasonable' under this rule

A player must not unreasonably delay play, either when playing a hole or between two holes.
A player may be allowed a short delay for certain reasons, such as:
• When the player seeks help from a referee or the Committee,
• When the player becomes injured or ill, or
• When there is another good reason.

I do not see 'because it is raining' as a good reason.

I do see pausing to put on waterproofs as a good reason.