Lloyd Jons said “If there is an earthquake forget your sermon and preach on the earthquake!”. On that occasion everywhere I went I preached on “there will be earthquakes in diverse places” (Matthew 24:7) and on the Philippian jailer who thought his life was going to end when an earthquake gave him pause for thought (see acts 16:23ff).
Now whenever I go back to India – which is probably twice a year – people come up to me and tell me that they were saved during that time of earthquake. The preacher must grab his chance. If there is a natural diaster the congregation is going to be more attentive on Sunday morning han ever before, but the preacher can only respond to the situation if he can preach on the topic without notice.
From the book "Preach the Word!: The Call and Challenge of Preaching Today"