Created a yum repo as followed:

$ more /etc/yum.repos.d/mongodb-org-3.2.repo
[mongodb-org-3.2]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/amazon/2013.03/mongodb-org/3.2/x86_64/
gpgcheck=0
enabled=1

Then :

$ sudo yum install -y mongodb-org
Loaded plugins: priorities, update-motd, upgrade-helper
amzn-main/latest | 2.1 kB 00:00
amzn-updates/latest | 2.3 kB 00:00
No package mongodb-org available.
Error: Nothing to do

Content of https://repo.mongodb.org/yum/amazon/2013.03/mongodb-org/3.2/x86_64/repodata/ seems pretty weird.