Agreed, the heavy rain is one thing, a Typhoon is another.
If you are going to be out in really heavy rain, consider getting some serious rain boots or leggings to go under a good quality poncho. It's standard scooter wear, but it works pretty well off the scooter. The colors are garish because of visibility issues on the scooter, but you won't look out of place... In heavy rain, the rain that splashes up will soak your feet regardless of your brolly - and even without wind.
I personally used cheaper umbrellas for a while, but recently found that 100-200 NT umbrellas can be even better. I get ones that have lots of spines and are slightly larger in coverage. They usually have a bit of a stronger spring, so have a bit of a more solid 'snap' when opening. However, I bought from a street vendor at a night market and the price was around half of what I had seen in stores for something similar.
Remember that you will need a new one each year since the metal is quite poor and will rust up on ya like crazy if it sits for any length of time even if you are diligent about drying it out.
A typhoon would tear even a strong umbrella to shreds (well, a real one anyhow). I always try to angle it so it is facing the wind, but a few years ago when we had typhoon Talim, I got caught in a downblast that just crushed it. That's pretty unusual, but so is wandering around in 180+ kph winds which are apparently strong enough to start pulling some street signs off.
If it's just for heavy rain, you could try waterproof sandals and any cheap umbrella - that's what the locals do.