Couldn’t find any US water leakage ratings in a quick web search. The US National Fenestration Council seems only concerned with energy gains/losses, etc. Canada has the CSA A440 Standard in its code in which all windows must be tested to meet at least the minimal requirements for water/air leakage and structure. Here’s a bit of an intro from a window company:
I would look for some Foamguard weatherstripping for the sides. The bottom corners may need more than this! If they were not tested for wind driven water leakage in an environmental chamber and re-designed as necessary, there may be not a lot that can be done with the existing doors excpet to install storm doors as a wind/rain break!!