Deluge
Etymology
From Latin "diluvium" ("flood"), from "diluere" ("to wash away"), via Old French "deluge." The same root underlies "diluvial" and echoes the biblical Flood.
noun · /DEL-yooj/
A great flood or an overwhelming downpour; figuratively, an overwhelming rush of anything.
What it names
Rain or flooding at its most overwhelming — and lends itself to any flood of messages, requests, or events.
Example
A deluge of emails greeted her after the vacation.
Related idea
A deluge overwhelms; a drizzle barely wets the ground — the two mark the extremes of rainfall.