Mrs. Armitage and the Big Wave by Quentin Blake, 1997.

Mrs. Armitage goes the beach with Breakspear in order to go surfing.  She explains to Breakspear that they have to swim out and wait for the “Big Wave.”  But, waiting takes longer that Mrs. Armitage expected, and soon Breakspear is tired, and they’re both hot.

Of course, Mrs. Armitage finds a solution for everything.  With an inflatable toy for Breakspear to ride on and some protective gear, they wait some more.  Needless to say, Mrs. Armitage doesn’t stop there.  As they wait for the perfect wave, there are plenty of other things that they need to keep themselves busy and make themselves more comfortable.

When the Big Wave finally comes, Mrs. Armitage not only makes an incredible show, but she also has what she needs to save a little girl who swam out too far and needed to be rescued.

The book is available to borrow and read for free online through Internet Archive (multiple copies, including one in Spanish).