Your beans are the first victim. Heat accelerates the staling process—oils oxidize faster, and volatile aromatics escape quicker. That's why a bag that tasted vibrant in spring can taste flat by July. Humidity is the second problem: it makes ground coffee clump, stick to the grinder, and flow unevenly through the puck. The result is a shot that's either sour (under-extracted) or bitter (over-extracted), with none of the sweetness you expect.