Thousands of rugby fans are expected to descend on the capital today as the four Welsh clubs compete head-to-head under one roof.
The Welsh Rugby Union said it expects 60,000 people to be at the Principality Stadium for Judgement Day VII.
Fans are warned they could also face travel disruption due to strong winds affecting transport networks.
A yellow warning covering Wales is in force until 3pm today.
The first game kicks off at 3pm with the Dragons taking on the Scarlets which is followed by Cardiff Blues v Ospreys.
Cardiff Council said all city centre roads will be closed from 1pm-8pm.
The WRU is advising ticket holders to get to their gate early for security checks.
Judgment day VII fixtures:
Dragons v Scarlets Kick off at 3pm
Cardiff Blues v Ospreys Kick off at 5:15pm
There will be a bus replacement service for train passengers travelling between Bristol and Newport – causing possible delays into Cardiff central station.
Cardiff Bus said it will be using alternative routes from 1pm and bus services will operate from Churchill way, Greyfriars road and Tudor street
The following city centre roads will be closed:
- Kingsway from its junction with North Rd to its junction with Duke St.
- Cowbridge Road East from its junction with Cathedral Rd to its junction with Westgate St.
- Tudor St from its junction with Clare Rd to its junction with Wood St
- Plantagenet St & Beauchamp St from their junctions with Despenser Place to their junctions with Tudor St
- Customhouse Street throughout its length.
- The following roads will be closed in their entirety: – Duke St, Castle St, High St, St.Mary St, Caroline St, Wood St, Central Sq, Westgate St, Quay St, Guildhall Pl, Golate, Park St, Havelock St & Scott Rd.
- Despencer St from its junction with Clare St
- Fitzhammon Embankment (access for buses and residents being maintained)
Tickets to the games are still available starting at £10 for U16s and £15 for adults.