The day of Ashura (10 Muharram 1443) will fall on 19 August 2021 corresponding to 11 Muharram 1443 of the Umm Al Qurra Calender (Makkah TV Date).
Saudi Arabia's calendar had predicted Muharram starting on August 9 but officials revised the date because it was not possible to see the moon on the evening before that.
Saudi officials adjusted the date rather than relying on what was forecast in their Umm al-Qura Calendar.

New Dates are as follows:
9th Muharram is on 18th August 2021
10th Muharram is on 19th August 2021
11th Muharram is on 20th August 2021

Jazak Allah Khair