This is due to a extreme red heat warning which is likely to have a significant impact on railway tracks, signals and embankments.
Waterloo line operator South Western Railway says customers urges customers to check before travelling today and only travel if essential on Wednesday and Thursday.
On all three days, fewer trains are set to operate across the SWR network. Trains that run are expected to be busier and journey times will likely be longer than usual, as trains run at reduced speeds.
SWR plans to update journey planners with an amended at 2am each day.
While the amended timetable is designed to help ensure scheduled trains run as planned, services may still be subject to further short notice changes and cancellations.
Temporary ticket acceptance is in place to travel at alternative times on the SWR network.
Visit the SWR website for the latest travel advice and ticket information before setting off.
Any customer who feels unwell should not board a train. If a customer feels unwell on a train, they should alert an SWR colleague and wait until the next appropriate stop to alight.
Stuart Meek, Chief Operating Officer of South Western Railway and Network Rail Wessex, said: “While we’ll be working hard to keep customers moving, the Met Office’s Red Extreme Heat Warning means an amended timetable will be in place with fewer trains on Tuesday, Wednesday and Thursday.
“In line with national travel advice, customers should check before travelling on Tuesday and only travel if essential on Wednesday and Thursday.
“If you must travel, please also remember take precautions like bringing a water bottle with you and not boarding a train if you are feeling unwell.
“We’re sorry for the disruption this extreme heatwave may cause your journey and thank you for your patience as we respond to these record-breaking conditions.”