Apple Inc's (AAPL  ) second quarter may look like a celebration of iPhone strength, but investors shouldn't mistake momentum for long-term muscle.

The Party Was Fun: iPhone Volumes Surged

According to JPMorgan analyst Harlan Sur, iPhone shipments tracked slightly ahead of expectations in the second quarter, driven by seasonal builds and strong consumer demand. But there's a twist-Sur believes the demand spike may have been fueled by a one-time trigger: a pause on smartphone tariffs.

That short window created an incentive for consumers and vendors alike to buy ahead, pulling demand into the first half of the year. Apple may have danced through the second quarter with stronger-than-expected volumes, but the lights could dim in the third.

Now Comes The Cleanup: Tariffs Could Bite Q3

Sur expects smartphone fundamentals to weaken in the second half of the year as the effects of pre-tariff hoarding fade and macro uncertainty kicks in. Sur warns that a combination of already-satisfied demand and renewed tariff uncertainty could reduce consumer purchasing power, just as Apple's next iPhone cycle ramps up.

That could spell trouble not just for Apple but for its key chip suppliers like Broadcom Inc (AVGO  ) and Qorvo Inc (QRVO  ), who rode the second quarter surge but may feel the sting if orders dry up in the third. These Apple-aligned names have benefited from early iPhone builds, but with signs of softening ahead, investors should brace for more muted updates in the coming months.

Don't Let Q2 Euphoria Cloud Q3 Reality

While Apple's June quarter may show solid beats, JPMorgan's analysis suggests it's less about sustainable strength and more about strategic stockpiling.

With trade and tariff uncertainty still hanging over the second half, the real test for iPhone demand-and the chip stocks tied to it-may just be getting started.