Scheduled Workflow Help

Hi experts, 

I have a a field called "ship date" which is a date field. 

Now, when a ship date is 2 weeks away, an email should be sent to the field "client email". This workflow should run every Thursday. 

So basically this workflow should gather all the projects where ship date is within 2 weeks and send an email to each "client email" every Thursday that satisfies the criteria.

How can I accomplish this requirement? Especially the part where I have to trigger the workflow on a specific day of the week (Thursday)? 

I am open to use a 3rd party workflow solution but a little hesitant on creating a custom workflow activity as it will require code.

Thanks,

Jon