Once satisfied, click one partition and name and format accordingly in HFS+ for the Mac requirements note: the HFS+ formatted partition will be recognized by Time Machine and you will be asked if that is your wish to use it you will probably answer 'yes' and allow TM to do its thing.
Grab the slider/divider to set the size limits to your requirements.
From the expansion list select 2 Partitions. (Be sure to select the topmost entry for the WD otherwise you will not have the Partition option.) It will show the Volume Scheme as Current with just the one partition that you did in FAT32. Go back to Disk Utility with the WD attached and follow a similar pathway as you initially did to format it, however this time you will choose Partition from the sub-menu. What is the capacity of the WD Passport? If it is sufficiently large (for example 1 or 2TB) you could partition it so that one section (partition) is formatted for Time Machine, and the other is left as FAT32 for the Windows portion.
