Widespread disruption affected Southern Rail services after trees fell across several parts of network, according to the operator.
Blocked sections were identified between Haywards Heath and Three Bridges, between Lewes and Brighton, and between Uckfield and Crowborough.
A lighting fault was also reported at Normans Bay station, while severe delays were recorded at every stop between Brighton and Seaford.
Southern Rail said additional forms of transport were being accepted for travel.
Brighton & Hove buses on routes 29, 29B and 29X were available for journeys to or from Brighton St Peter’s Church, Moulsecoomb, Brighton University, Falmer, Lewes Post Office or Law Courts, Uckfield, Crowborough, Eridge and Tunbridge Wells.
Metrobus route 272 covered Brighton, Preston Park, Hassocks, Burgess Hill, Wivelsfield, Haywards Heath, Three Bridges and Crawley.
Stagecoach route 701 served Littlehampton, Angmering Town, Durrington Town, Goring by Sea, West Worthing, Worthing, East Worthing and Lancing.
Southern trains linking Southampton Central, Brighton and Lewes with London were among the affected services, along with Thameslink trains running between Brighton and London.
South Western Railway services from Southampton Central to Portsmouth Harbour and London Waterloo were also included, as were London Underground links connecting terminals.
Thameslink and Gatwick Express operations were disrupted by the tree that came down between Burgess Hill and Haywards Heath.
An update from Southern Rail stated that all lines were blocked until further notice because of the obstruction between Haywards Heath and Three Bridges.
The Brighton and Lewes route was subsequently reported to have reopened, although the Haywards Heath to London section remained blocked.
Significant disruption also continued on lines linking Brighton with Gatwick.
The Argus sought further information from Southern Rail about how the disruption was being managed during Storm Austen.