Here's what's happening: when the air is warm, your kettle loses heat quicker, and the water temperature drops faster once you pour it into the press. Lower water temperature means less extraction—so your coffee comes out underdeveloped and thin.

You might also be grinding coarser without noticing. In summer, some folks switch to a coarser grind thinking it'll cool faster, but that just makes the water run through too quickly and leaves the grounds under-extracted.

And then there's the ratio. When it's hot, you might instinctively use fewer grounds to avoid a heavy cup—but that's the opposite of what you want. Less coffee means weaker flavor, period.