I am having a tough time visualizing what you are dealing with.

Can you post up a picture or a bit more detailed explanation?

That window looks to be so poor, I would not be surprised if your issues were due to condensation even in rain-temps.

How cold is it there right now?

Condensation is certainly an option as is the internal glazing bead and weeping of the IGU set.

Is the drywall going up over the frame?

57 was the high while 43 the low two days ago. indoor temp at night while sleeping was only 60.

Yesterday, high 48, 41 low. 60 at night. I found the water puddle yesterday morning. When windowsonwashington asked me to post a picture, I took the shot while finding the new puddle again about 9 PM. Day through evening time, I kept indoor temp about 68.

This window is about 61" wide by 45" high. It's the middle section of the bay window unit, with 2 windows on both side with a tilt. No water puddle found at any other window, except little condensation found at the overlapping double pane frame in the middle. Yes, the drywall is going up over the frame.

What is the indoor humidity level?

Those temps seem a bit mild for condensation issues but if the humidity is high in the home, it can raise the dew point temp pretty high.

humidity around 65, up or down a little

That is pretty high.

At 65%, you can get dew point at 55 degrees. If it is in the 30's outside, you glass is going to be at least that low.

Here is a link that might be useful: Dew Point Calculator

I see. Thank you

Not an expert here, just a homeowner with a similar experience...water on our windowsill after a heavy rain, but not always... just sometimes. It wasn't a problem with the window, or the flashing, or the roof above the window. From what we could tell, the problem stemmed from an upper roof, that dripped onto a lower roof that was above the window. The heavy rain would come off the upper roof and splash onto the lower roof with such force that it was bouncing back against the house clapboard. We're guessing that the water was somehow getting behind the clapboard and following the easiest path downward, by gravity, until it came out at the trim at the top of our window and dripped onto the sill. It took us quite a while to figure this out (and it is all really just a guess anyway), but the problem was solved when we put a small section of gutter on the upper roof. No more dripping water... no more leaking window.

Water is funny. It may not come from where you think it would. During a renovation a few years ago, we had a heavy rain before a small section of the roof was entirely finished. Third-story roof, but the water leaked through a doorway in the middle of our first floor... nowhere near an outer wall.

I hope this helps!

Good point littleriverbb!!

Water is a tricky little devil and where the leak shows can be far from where it starts.