Transpacific Cruise Weather: Are Pacific Crossings Rough in September, October and May?

Transpacific cruise weather depends far more on which route you take than on the month. The northern route between Alaska and Japan runs close to the Aleutian Islands through one of the stormiest stretches of ocean in the world, and it is cool, often foggy and the likeliest to be rough. The southern routes through Hawaii and the South Pacific are warm, with trade-wind seas that are usually moderate. Both have tropical storm seasons to watch.

By month, September and the spring window of late April and May are usually the calmest times for a Pacific crossing. October brings more North Pacific swell and a lingering risk of typhoons near Japan. Most passengers on a large ship see a day or two of noticeable motion on a two-week crossing, not a voyage of constant heavy seas.

The two transpacific routes and their weather

Ships cross the Pacific on two broad routes, and the weather on each has very little in common. Our transpacific repositioning cruise schedule lists the individual sailings.

In our sailing data, built from the cruise lines’ own sites, the busiest departure months for transpacific voyages are April, September and October, in that order. That timing is deliberate: lines move ships between the Alaska season and the Asian or Australian summer in the shoulder months, before the North Pacific turns wintry and after the South Pacific cyclone season ends.

Why the North Pacific route gets rough

The great-circle route from Seattle or Vancouver to Tokyo bends north past Alaska because it’s shorter, and that takes ships through the storm track of the North Pacific. In fall and winter, low-pressure systems form off Japan and run northeast toward the Aleutians and the Bering Sea. Even when a ship misses the storm itself, those systems send long swells hundreds of miles across the route.

NOAA’s marine weather reviews track the strongest of these storms, the ones that reach hurricane-force winds of 64 knots or more without being tropical. A study cited in the NOAA North Pacific marine weather review found these hurricane-force lows were most frequent in December, and individual seasons often peak in January or February. October is already active, and activity falls off by April. For a cruise passenger, that means a September crossing usually sees the gentler end of the season, October more swell, and a spring crossing in late April or May catches the decline.

Temperatures stay cool either way. Expect the 40s and 50s °F on deck near Alaska and on the open crossing, and frequent fog and low cloud. Scenic cruising in Alaskan fjords can be spectacular one day and a gray wall the next. Our guide to repositioning cruises to Japan and Asia walks through the route port by port.

Transpacific cruise weather in September

September is the most popular month for westbound crossings to Japan, and for good reason. The North Pacific is cooling but the big winter storms haven’t set in, so most sea days are moderate. Fog is common near the Aleutians and off Hokkaido.

The catch is at the Japan end. Typhoon formation in the western North Pacific peaks in August and September: the Japan Meteorological Agency’s climatology gives 1991 to 2020 averages of 5.7 tropical cyclones forming in August and 5.0 in September, out of about 25 a year. Most don’t hit Japan, but a storm nearby can move or cancel a port call in Hokkaido or northern Honshu, or delay arrival in Yokohama.

On the Hawaii route, September is hot. Honolulu’s normal daily high is in the upper 80s °F, and the central Pacific hurricane season is still running. Hurricanes that threaten Hawaii are uncommon, but they do happen, and ships reroute around them.

Transpacific cruise weather in October

October is a transition month and the one most likely to bring a rough day on the northern route. North Pacific storms grow more frequent through the month, and a crossing late in October has a real chance of meeting a large swell. Air temperatures near Alaska drop into the 40s °F, and outer decks may be closed in strong wind.

Typhoons are less frequent than in September, with the JMA average down to 3.4 forming in October, but they still form and some recurve toward Japan. Ships sailing from Japan to Los Angeles via Hawaii in October, or from Los Angeles to Japan via the Hawaiian islands, take a more southerly path and usually have warmer, easier conditions.

For the South Pacific, October is a good month. Hawaii to Sydney or Brisbane sailings, covered in our guide to Australia repositioning cruises, arrive before the South Pacific cyclone season begins in November, and the islands are warm and mostly dry.

Transpacific cruise weather in April and May

Spring crossings run the other way: from Tokyo to Vancouver in late April and May, and from Sydney or Brisbane to Hawaii and the West Coast in April. These are usually the calmest transpacific voyages of the year.

• Japan to Alaska and Vancouver: the North Pacific storm season is winding down, and typhoons are rare in April and May (the JMA averages are 0.6 and 1.0 a month across the whole western Pacific). It is cold near Alaska, with snow still on the mountains, so pack for winter on deck.
• Australia to Hawaii: ships leave at the tail end of the South Pacific cyclone season. NIWA, New Zealand’s national weather research agency, describes the season as running usually from November to April, with peak activity in January to March, so an April departure carries a small, falling risk.
• Hawaii to the West Coast: the last leg is cooler and can bring a lively day or two as the ship moves north out of the trade winds toward California or British Columbia.

Typhoons, hurricanes and cyclones: what the ship does

The Pacific has three tropical storm seasons, and a long crossing can touch more than one.

Season dates for the eastern Pacific come from the National Hurricane Center’s climatology. Cruise ships have forecasters’ data and a lot of ocean to work with, so the usual response to a tropical storm is to steer around it. That can mean a skipped or swapped port, a changed order of calls, or an arrival a few hours late, rather than a voyage through the storm. Cruise contracts allow lines to change itineraries for weather, and compensation for a missed port is usually limited to a refund of that port’s fees and taxes.

Seasickness on a long Pacific crossing

The CDC’s motion sickness guidance applies on the Pacific just as on any sea. Avoid the bow, keep your eyes on the horizon, get fresh air, and go easy on alcohol. For medication, the CDC lists antihistamines such as meclizine and dimenhydrinate and the prescription scopolamine patch, which works best started before symptoms. Talk to your doctor or pharmacist before the trip, especially if you take other medicines. Our article on whether transatlantic cruises are rough covers the same advice in more depth, and it applies here too.

A few points are specific to the Pacific. The long North Pacific swell has a slower, rolling motion that some people adapt to within a day and others find harder than a short, choppy sea. Five or six sea days in a row also mean there’s no port day to recover on. And the cold on the northern route shuts outdoor space, which is where many people feel best when the ship moves, so plan on a midship lounge with a view of the horizon.

How to pick a calmer transpacific crossing

1. Choose the southern route if motion worries you. A crossing via Hawaii is longer but usually gentler than the northern great-circle route via the Aleutians.
2. Prefer September or spring on the northern route. Early September westbound and late April or May eastbound avoid the heart of the North Pacific storm season.
3. Book low and midship. A cabin on a lower deck near the middle of the ship moves least. Side doesn’t matter for motion.
4. Pick a larger ship if you can. Bigger ships with stabilizers handle swell better, though no ship is immune to a big Pacific swell.
5. Pack for the cold even on a “Pacific” cruise. The northern route needs a warm waterproof jacket, a hat and gloves. See the crossing packing list for layering for two climates.

If you’re torn between routes, the deciding question is whether you want Alaska and northern Japan or warm islands. The northern route trades comfort at sea for scenery and a shorter crossing; the Hawaii and South Pacific routes trade sea days for sunshine. Either way, plan your sea days around a few rough hours rather than expecting them never to come.