Why were Jehovah's Witnesses holding a Memorial Service for Jesus on Tuesday, March 26 2013?

“How Should We Remember Jesus’ Death?”, The Watchtower, March 1, 2012, his this to say:

When should we commemorate Jesus’ death?

Jesus’ death occurred on Passover, Nisan 14. A Jewish day begins at sundown. The evening before he died, Jesus ate the Passover meal with his apostles and then instituted a new memorial meal to commemorate his death.—Read Luke 22:14,15.

Today, God’s people commemorate what God provided through Jesus to set the whole world free from sin and death. (Exodus 12:5-7, 13, 17) Just as the Passover was observed once a year, so the Memorial of Jesus’ death is held once a year after sundown on Nisan 14 according to the Bible’s lunar calendar.—Read John 1:29.

You are invited to attend the Memorial.

Please view further information and collection of Witness publications on the Lord’s Evening Meal.

This year the date for this annual memorial of Christ’s death falls on Wednesday day March 23 2016.

Since the ancient Jewish lunar calendar counted the start of a new month from the first observable manifestation of a new moon the timing is some what later than a scientific calculation of the exact phases of the moon. Usng the same method the Jehovah's Witnesses calculate the start of Nisan and count forward to the 14th of Nisan.

Another reason the date of the 2016 Memorial occurs on a different date from the Jewish Passover is that the Jewish year corresponding to 2015-16, namely 5776, is the 19th year of a 19-year calendar cycle, and is therefore designated as a 13-month leap year. The Jewish Calendar cycle designates the 3rd, 6th, 8th, 11th, 14th, 17th and 19th years as leap years. As a result, the Passover celebration is postponed by one lunar month, occurring on April 22th instead of March 24th, thus also one lunar month later than the Memorial celebration.

That date is aligned with the corresponding date on our modern calendar so it varies each year. However that it is accurate is shown by the fact that this date is always the date of the first full moon following the spring equinox which was the official Passover date on which Jesus instituted the new covenant. When you step out side on what ever date the memorial is on you will see a bright full moon (weather permitting).

The memorial ceremony can start before sundown but the passing of the emblems (bread and wine) must commence after sundown since that is when a new day began on the ancient lunar based calendar..

This is the most important event of the year in Jehovah's witnesses lives. The attendance worldwide dwarfs the official number of Jehovah's Witnesses since many newly interested persons and family members of active Witnesses will come. Additionally many formerly active Witnesses will come to this annual event.

A three week long campaign is engaged in each year to invite as many people as possible to come and learn about how the death of Jesus Christ can benefit each one of us.

Follow this link to read your invitation to this years memorial and find a location near you to attend. https://www.jw.org/en/jehovahs-witnesses/memorial/

In Exodus 12, the Hebrews celebrated the Passover on the 14th day of the first month of the year, it is called Abib in Hebrew (like January in our calendar today). After coming back from the Babylonian exile, they call Abib by a Babylonian name which is Nisan. So Abib 14 or Nisan 14 every year is the day of the Passover.

Fast forward to the time of Jesus, he celebrated Passover which is Abib 14 and he died on that very same day. Remember that in the Bible, a day starts from sunset and ends on a sunset.

Abib 14 can be any day of the week every year. Like July 4th, the day varies from year to year but it is always July 4th.

Jesus did not die on a Good Friday, there is no biblical basis for such doctrine, although it would look like that if you are not really familiar with the Jewish customs and traditions.

Apparently, per Wikipedia, this date corresponds to Nisan 14, converting the date from the Hebrew Calendar to the Gregorian Calendar.

I don't believe they're saying it happened on a Tuesday. In 2012, it was a Thursday.