On its Digital Blog, TfL notes that it chose Thursdays because that's when travellers tend to look for weekend travel advice. Requests apparently peak at around 5pm on that day. With this in mind, the authority will send a direct message full of travel information to subscribers' Twitter accounts, a method that is convenient but not overly intrusive.
To sign up, customers need to subscribe to @TfLTravelAlerts updates via TfL's Twitter Alerts page. Once subscribed, users can pause alerts (if they're not aren't in London that weekend) or subscribe to real-time updates from all of London's Tube and rail lines.