Sum with multiple conditions

[Coldones]

I'm having a hard time coming up with the correct formula for this scenario:

If cell A1 has the word SEPTEMBER, I want to be able to sum cells D3:D26 on a separate tab. And then if cell A1 has the word OCTOBER, I want it to sum cells D27:D40. This will continue for each month of the year so in reality there's going to be 12 different ranges of cells that are summated based on whatever month cell A1 represents.

(Cell A1 is basically just a link to whatever month is selected from a drop down box on another tab)

Thanks.