According to Sunni Muslim tradition, Ibn Abbas narrates that Muhammad came to Medina and saw the Jews fasting on the tenth day of Muharram. He asked, “What is this?” They said, “This is a good day, this is the day when Allah saved the Children of Israel from their enemy and Musa (Moses) fasted on this day.” So he fasted on this day and told the people to fast." Read more about this day and the immense merits of fasting on this day.
According to the Fiqh Council of North America, the first of Muharram 1435H will be this Monday, Nov. 4, 2013. Therefore, the Day of Ashura will be on Wednesday, Nov. 13, 2013.
That means it is best to fast on either Tuesday (12th) and Wednesday (13th) or Wednesday (13th) and Thursday (14th).
A humble reminder for us to plan our schedules next week so we can take advantage of a the manifold blessings from a fast on these two days.