When encountering a precipitation chart in Weather, there is a delay between swiping left or right and hearing VoiceOver speak the contents of the focused element. In some cases, after swiping several times, VoiceOver focus may move to the "Show map" button near the bottom of the screen.
Open Weather and focus on a precipitation chart, labeled as "Next hour precipitation," and swipe right several times. Note that this will only be visible if there is currently precipitation happening or forecasted in the next hour in the selected location.
With the rotor set to navigate by containers, swipe down passed the precipitation chart to another container, such as hourly forecast. You should then be able to navigate the app normally.