Anyone know of a dead rat that will fit over the WST50?
I've recorded in the Midwest with these when the gusts were bending trees (easily over 30 mph) and never had wind noise.
Where are you recording that you would need that much protection? On the beach? Mountaintop?
Movos are quite good at reducing wind noise, but not infallible. First check that its working as well as it should. Check that the flexible rubber cuff-seal to the microphone body is tight and lot letting any air leak through. A leak in that area will prevent any windscreen from working well. Secondly, be careful not to insert the mic all the way as far as it will go into the Movo. Instead leave an bit of airspace inside between the end of the mic and the front of the windscreen. Addressing those things may eliminate the wind noise without needing a furry cover. They've improved wind performance for me.
As you are probably aware, the closer the directional pattern of the microphone is to the fig-8 end of the polar-pattern spectrum and the farther it is from omni, the more susceptible to wind noise it will be. Even after doing the things mentioned above I've gotten some wind noise in supercards, shotgun mics and fig-8's when recording outdoors in gusty condition. So if it makes sense, you might switch to a more open pickup pattern when it gets especially windy.
Because both of the mic elements of the stereo shotgun I use are wind susceptible due to their patterns, I have a few windscreen options for that microphone. I typically use a standard Movo same as WT50 only longer. Rather than make a furry cover to go over that, I picked up a second fur-covered windscreen to use in especially windy conditions. The furry one looks like a Movo with the same rubber cuff and interior foam, but is actually some other brand. I mention that because if the tips about use are not enough, switching to a dedicated furry Movo when needed may be a better answer than throwing furry covers on your existing Movo pair.
When things have gotten really windy, I've pulled out some old handmade furry covers that someone on the board made years ago to fit big ass Shures and used those on the smaller WT50s that are also used in the rig. Worked. I've similarly used a Rycote BBG furry cover, which has much better fur, better construction and features a cinch string opening that makes it easy to snuggly secure around the MT50. That thing works great, but isn't cheap. Fortunately I already had it on hand and repurposed it for this.
Hope that helps.