If you do a word search in the Bible for a "13th month", you will not find it because it is not there.
The moon's orbit around the earth takes 29 days 12 hours and 44 minutes per month, or 29.5 days. A lunar calendar has 354 days in a year, and about every 3 years, we have to add a 29 or 30 day month, making a 383 or 384 day year, in order to stay in the spring growing season (Abib).
Our modern solar calendar (The Gregorian Calendar) has 365 day in a year, this calendar is 11 days longer than the lunar calendar. It seems as if in the days of Noah, the months were 30 days each. The water began to flood the earth on the 2 month 17th day according to Genesis 7:11. It began to go away after 150 days in the 7 month 17 day Genesis 8:3-4 (after 5 months). 150 days divided by 5 Months = 30 days per month.
YAH moved the shadow backwards on the sundial 10 degrees, changing the month from 30 days each month to 29 or 30 day each month. The moon still operates this way today. See Isaiah 38:1-9, 2nd Kings 20:1-21, 2nd Chronicles 32:24-33. Is there a 13th month that can be proven from Scripture?
So far, the only proof I have seen of a 13th is from the Book of Ezekiel. Pay attention to the dates carefully. Ezekiel 1:1-2 states that YAH spoke to him in the 4th month on the 5th day of the month in the fifth year of King YAHUiachin.
Ezekiel 3:16 “And it came to pass at the end of seven days that the word of YAH came to me, saying…” This is when the time starts by adding in the 7 days we have the 4th month and the 12th day when the 430 days were to start.
Ezekiel 4:1-11 YAH decreed to Ezekiel: lay on his side 390 days then to lay on the other side 40 days for a total of 430 days.
Ezekiel 8:1 he is in his house on the 5th day of the 6th month of the 6th year. 1 year 1 month and 23 days later, Ezekiel is seated before the Elders on the 5th day of the 6th month of the 6th year. Now let’s count from the 12th day of the 4th month of the 5th year to the 5th day of the 6th month of the 6th year; this is 13 months and 23 days or 1 year 1 month and 23 days.
Let's count the days
It is impossible for Ezekiel to fulfill the 430 day on our Gregorian Calendar of 365 days in a year + 30 days and then 23 days from the 12th day of the 4th month in the 5th year and have been in his house before the Elders on the 5th day of the 6th month of the 6th year? Let’s count... 365 + 30 + 23 days = 418 total days; this would be short at least 12 days of the 430 days.
It is impossible for Ezekiel to fulfill the 430 day on a Lunar Calendar of 354 days in a year + 30 days and then 23 days from the 12th day of the 4th month in the 5th year and have been in his house before the Elders on the 5th day of the 6th month of the 6th year? Let’s count... 354 + 30 +23 days = 407 total days; this would be short at least 23 days of the 430 days.
Now to see if the Lunar-calendar will work with a 13th month added about every 3 years to accomplish this 430 day time period. A 12 month Lunar calendar has 354 days in a year + this year had a 13th month in it so we add + 30 days = 384, so this year had 384 days in the year.
Now this is the 5th day of the 6th month of the 6th year, so we add the 384 + 30 days +23 days = 437 or 436 if one of the extra month only has 29 days in it. We can see that Ezekiel could have fulfilled the 430 days that YAH command him, and was seated before the elders in Ezekiel 8:1 with 6 or 7 days extra. This shows that the previous year had a 13th month according to the Book of Ezekiel.
If we do not add an additional month (13th month) to our lunar calender, then our seasons will be out of season by 10 days each year. See what would happen if an extra month is not added to a lunar calendar every three years. Look at the lunar calendar below starting from 2014.
If an extra month is not added to the calendar after every three years, then the first month of the scriptural year would eventually begin in winter.