Winter swell isn't the only thing that cancels Kona
Kona has no deep-draft harbour, so the ship anchors in Kailua Bay and everything depends on the tenders. Swell is the usual culprit, but not only in winter: in June 2022 Pride of America skipped its call because a south swell was running straight into the bay under a high-surf advisory. In March 2017 the same ship skipped Kona because of unusual southerly winds gusting around 33 mph, which made tendering unsafe.
Volcanic air has done it too - in May 2018 Norwegian dropped a Kona call over poor air quality during the Kilauea eruption, a single skipped visit the island's visitors bureau put at about $175,000 in lost business. The practical upshot is to treat any Kona plans as provisional, and to check an independent operator's weather-cancellation terms before paying.
The open-air trolley along Alii Drive
If you want to go further than the walk along Alii Drive, the county's Hele-On Route 201, the Kona Trolley, stops at Kailua Pier. When it launched in 2021 it ran hourly from 7am to 9pm, seven days a week, between Kona Commons and the Sheraton at Keauhou, with a $2 fare. You can flag it down at safe spots between stops. Hourly service means checking the return times against all-aboard, since missing one costs you an hour.
Sources: westhawaiitoday.com, hawaiitribune-herald.com, bigislandnow.com, westhawaiitoday.com