Well, you could look to celestial bodies for such a thing. But you could look much closer to home. Chinu already touched on super volcanoes, but why does it have to be so epic? Let me paint two picture for you, both of which might well answer your question.
First - The personal apocalypse. In this scenario, you don't need the world to end, just the world of your protagonist, or whomever you're central point of view follows. In this case, just a typical (if somewhat extreme) volcanic eruption or earthquake can/will/may meet your criterion. For example, major earthquake near a string of active volcanoes. It could be argued that the earthquake (i.e. the sudden shift of a tectonic plate) forces a pocket of magma to be shot up through the already present 'channel(s)' to the volcano(es), causing said volcano(es) to erupt (https://www2.usgs.gov/faq/categories/9840/2554). There's your rain of fire, and eruptions can last for hours, days, weeks, or even years dependent on a number of factors (http://volcano.oregonstate.edu/how-long-do-eruptions-last). Then, if the earthquake does something bad, you get your flood in the form of a tsunami.
Now, this first route may or may not be the world ending apocalypse you seek, but they have ended cities, even civilizations. Though, it does have the potential to be as catastrophic as you desire. Personally, I see it more as a... well, personal apocalypse. That is to say, MY city, MY world is ending.
The other - global apocalypse. Let's take the moon crashing into the earth scenario? But really, this applies to any large body. The closer the large body gets to the planet, the more each body's gravity will malform the other. That could be one plausible explanation for the flood (gravity pulling on the water, creating flood tides). Or a much simpler one would be a large object hitting the moon first, alter its orbit and sending it hurdling into the earth (or perhaps just sending large chunks towards the earth in an armageddon-styled rain of death).
If you go with the celestial body route, I would advise you studying up on the plausibility of it. Don't go with a 'meteor shower raining down on earth', though. It's highly unlikely, because anything large enough to really create the damage your question implies, its gravity would likely cause it to 'absorb' other similar-(and most definitely smaller-)sized bodies. One plausible reasoning, could be that it (just like my previous 'moonstruck scenario') was first struck by another body, altering its course, and perhaps breaking it into smaller bits, for the 'rain of fire' you're looking for. Some bits might well arrive well before others, so that could stretch it out over the course of many days.
Hope this helps ^_^