Shimanami Kaido Weather by Month: Climate, Wind & What to Wear

When is the best time to cycle Shimanami Kaido? Based on monthly climate data from a local cyclist — May and October top the ratings. Covers temperature, rainfall, wind direction by season, and a practical clothing guide for each time of year.

Weather on Shimanami Kaido

Monthly data on climate, rainfall, and wind

When planning a cycling trip on Shimanami Kaido, weather is usually one of the first things on your mind. You probably don’t want to get rained on. You’d rather not battle a headwind and drain your energy. Is the rainy season a concern? What about typhoons? Is it too cold in winter? These are all very reasonable things to wonder about — and I’d love to help you sort them out before you arrive.

Shimanami Kaido sits within what is known as the “Setouchi Climate Zone” — a region characterized by relatively mild temperatures and low rainfall year-round. That said, each season has its own distinct character. Understanding the temperature, rain, and wind patterns in advance will make planning your trip a whole lot easier.

On this page, I’ve used weather data from three points along the route — Imabari, Omishima, and Ikuchijima — to summarize monthly climate conditions, wind direction, cycling conditions, and what to wear. Looking at the data, the clearest and calmest cycling conditions tend to fall in May and October.

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Monthly recommendation summary

Let me start with the conclusion. The table below gives an at-a-glance recommendation rating for each month, factoring in temperature, rainfall, and wind. If you’re trying to decide when to visit, this should give you a good overview to start with.

Month	Avg. Temp (°C)	Rainfall	Prevailing Wind	Wind Conditions	Rating
Jan	6.2°C	Low	W to NW	Strong winds frequent	★★☆☆☆
Feb	6.7°C	Low	W to NW	Strong winds frequent	★★☆☆☆
Mar	9.8°C	Somewhat low	W to NW	Somewhat strong	★★★☆☆
Apr	14.8°C	Moderate	NE to E	Calm	★★★★☆
May	19.2°C	Somewhat low	NE to E	Calm	★★★★★
Jun	23.1°C	High (rainy season)	S to SW	Calm to somewhat strong	★★★☆☆
Jul	27.2°C	Low after rainy season ends	SW to W	Calm	★★★☆☆
Aug	28.7°C	Low	S to SW	Calm	★★☆☆☆
Sep	25.1°C	Somewhat high (typhoons)	Variable	Strong during typhoons	★★★☆☆
Oct	19.6°C	Low	NE to E	Calm	★★★★★
Nov	14.1°C	Low	NE to E	Calm	★★★★☆
Dec	8.7°C	Low	W to NW	Getting stronger	★★★☆☆

* Based on publicly available data from the Japan Meteorological Agency (JMA) — averages of three stations: Imabari, Omishima, and Ikuchijima. Values vary year to year. Ratings are the author’s personal assessment based on a comprehensive evaluation of temperature, rainfall, wind, and overall rideability.

May and October come out on top with five-star ratings. Both months offer average temperatures around 19–20°C (66.2–68°F), low rainfall, and calm winds — honestly the best conditions you could ask for when cycling. August, on the other hand, is calm in terms of wind, but the average temperature of 28.7°C (83.7°F) makes it quite a tough month. January and February are surprisingly dry, but persistent westerly and northwesterly seasonal winds can make conditions on the bridges quite demanding.

For a more in-depth look at the best season, I’ve also written a separate article: “Best Season for Shimanami Kaido Cycling.” On this page, I’ll dig into the conditions month by month and season by season.

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The Seto Inland Sea is naturally sunny

Characteristics of the Setouchi climate

The coastal region where Shimanami Kaido is located belongs to what meteorologists call the “Setouchi Climate Zone.” Flanked by the Chugoku Mountains to the north and the Shikoku Mountains to the south, the area is naturally sheltered from moisture-carrying air masses — meaning it receives significantly less rain throughout the year compared to the Pacific coast or the Sea of Japan side of Japan.

The annual average temperature in the region is around 16–17°C (61–63°F) — a mild, dry climate. Summer highs can exceed 35°C (95°F), but snow accumulation in winter is rare. From a cycling perspective, there are very few months that are truly off-limits, making it one of the more versatile cycling destinations in Japan year-round.

Weather can differ between the Imabari side and the Onomichi side

Living here, I’ve often noticed that the weather on the Ehime side (Imabari) and the Hiroshima side (Onomichi) can be quite different at the same time. “Sunny in Imabari, raining in Onomichi” is actually not that unusual. Shimanami Kaido spans about 70 km across two prefectures, and depending on how a weather front is moving, conditions can shift from island to island as you ride. Experiencing that gradual change in weather is actually one of the unique charms of cycling this route.

When checking forecasts, I’d recommend looking at multiple locations — such as Imabari, Onomichi, and Fukuyama — to get a more accurate picture of what to expect along the route.

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Rain-free on roughly 3 out of every 4 days

Just how little rain falls here — by the numbers

According to weather data, around 75–80% of days in the Shimanami Kaido area — or roughly 280 days per year — see virtually no measurable precipitation.

Simply put, it doesn’t rain on about 3 out of every 4 days. Days with 10mm or more of rainfall — the kind that would realistically force you to cancel a ride — occur only around 28 days per year. That works out to roughly once every 13 days.

Monthly cycling conditions at a glance

Here’s how the number of days in each category breaks down by month: “sunny days,” “overcast but rideable,” “unstable,” and “rain cancellation level.”

Month	Sunny days	Overcast (rideable)	Unstable	Rain cancellation level	Notes
Jan	16	10	3	2	Driest month of the year
Feb	15	9	4	3	Continued dry trend
Mar	16	10	3	2	Spring rains beginning to pick up
Apr	17	8	3	3	Watch for passing low-pressure systems
May	18	8	3	2	Sunny days are consistent
Jun	11	9	5	5	Rainiest month — Japan’s rainy season (tsuyu)
Jul	16	7	4	4	Clear skies once the rainy season ends
Aug	20	6	3	2	Fine weather continues unless a typhoon hits
Sep	15	8	4	4	Risk of direct typhoon hit
Oct	18	8	3	2	Many clear autumn days
Nov	17	9	2	2	Stable fine weather continues
Dec	16	11	2	2	Winter pressure pattern: dry and sunny

* Based on publicly available data from the Japan Meteorological Agency (JMA). “Rain cancellation level” is defined as days with 10mm or more of rainfall. Values vary year to year.

Even in January, there are 16 sunny days — while June, during Japan’s rainy season (tsuyu), drops to just 11, making it the lowest month of the year. Even so, around 20 days in June are still rideable, so don’t give up on June entirely. With proper rain gear and a flexible attitude about timing, you can definitely have a good ride.

Rainy season on Shimanami Kaido: how much rain does it actually get?

Japan’s rainy season (tsuyu) typically begins in the Shimanami Kaido area in early June and ends around mid-July, though the timing varies from year to year. Even during this season, sunny days are more common than you might expect. I’ve actually cycled during the rainy season and experienced mornings with rain that cleared up by the afternoon. Delaying your start a little and keeping an eye on conditions can be a good strategy.

One upside of the rainy season is that there are fewer visitors — which means rental bikes and accommodation are generally easier to book. Choosing to visit in June and enjoying a quieter Shimanami Kaido with good rain gear is a perfectly valid option, in my opinion.

Typhoon season (August–October): what to watch out for and how to handle it

Typhoons tend to be most impactful from late August through September, though they can occasionally arrive in October as well. Strong winds and heavy rain can lead to bridge closures, so I’d recommend keeping a close eye on typhoon updates through the Japan Meteorological Agency (JMA) website or apps like Windy.

If a typhoon approaches while you’re in the middle of your trip, don’t push through it — staying put at your accommodation or using ferries and buses to relocate is the right call. Shimanami Kaido is actually well set up for bailing mid-trip from any island via public transport, so knowing that option is there in advance will give you peace of mind.

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Wind patterns and choosing your starting point

Shimanami Kaido has clear seasonal wind patterns

Alongside rain, wind is one of the factors that has the biggest impact on cycling. You can deal with rain by wearing a good waterproof jacket, but a strong headwind feels like climbing a hill that never ends. And since Shimanami Kaido involves crossing multiple long bridges, you get the full force of the wind with nowhere to hide.

There is a clear seasonal pattern to the wind along Shimanami Kaido. From winter into spring, westerly to northwesterly winds tend to strengthen (averaging around 3.0 m/s), while from summer into autumn, winds often shift to a calmer easterly direction (averaging around 2.5 m/s).

Simply knowing this pattern can really help when deciding where to start. In short: starting from Imabari (the Ehime side) tends to be more advantageous in winter and spring, while in summer and autumn, either starting point works well.

Monthly wind characteristics

Month	Prevailing Wind	Avg. Wind Speed (m/s)	Strong Wind Risk	Starting Point Tip
Jan	W to NW	3.0	High	Imabari start recommended ◎
Feb	W to NW	3.0	High	Imabari start recommended ◎
Mar	W to NW	3.0	Medium–High	Imabari start recommended ◎
Apr	NE to E	2.5	Low–Medium	Either start works fine
May	NE to E	2.5	Low	Either start works fine
Jun	S to SW	2.5	Low–Medium	Either start works fine
Jul	SW to W	2.5	Low	Either start works fine
Aug	S to SW	2.5	Low	Either start works fine
Sep	Variable	2.5	Low → High (during typhoons)	Always check typhoon forecasts
Oct	NE to E	2.5	Low	Either start works fine
Nov	NE to NW	2.5	Low–Medium	Either start works fine
Dec	W to NW	3.0	Medium–High	Imabari start recommended ◎

* Based on data from three stations: Imabari, Omishima, and Ikuchijima. Wind direction shown is the most frequently occurring direction. Actual conditions vary by location due to the terrain of each island.

My own mistake: a headwind that forced me to bail at Omishima

Not checking the wind forecast in advance once cost me — I want to share this as a cautionary tale. In early spring, I stayed overnight in Onomichi and set off the next morning heading toward Imabari. What I hadn’t anticipated was just how brutal the headwind would become.

It was late March, and the day started off beautifully sunny. But around Innoshima, the wind picked up. By the time I reached the Tatara Bridge (Tatara-Ohashi), I was pedaling hard but barely making progress. More than the physical exhaustion, it was the slow creeping frustration that got to me. I ended up folding my bike and boarding a highway bus from the Omishima bus stop toward Imabari.

The weather forecast that day had shown clear skies with 0% chance of rain — but there was a forecast of “strong westerly winds building from late morning” that I simply hadn’t checked. It taught me a lesson I haven’t forgotten: a sunny forecast doesn’t mean a comfortable ride. Wind direction matters just as much as whether it’s going to rain.

If you’re planning to start from Onomichi and ride toward Imabari in early spring (March–April in particular), please make sure to check the wind direction forecast the night before.

Why is it always windier on the bridges?

One of the things that makes cycling Shimanami Kaido unlike most other routes is the experience of crossing the bridges themselves — but those bridges tend to be significantly windier than the roads on the islands. The reason is simple: the bridges span open water with nothing to block the wind. On land, buildings and trees provide natural wind breaks. The moment you ride out onto a bridge, crosswinds and headwinds hit you full-on.

I’ve lost count of how many times I’ve thought “the wind is calm today” while riding on an island, only to be hit by a strong gust the moment I enter a bridge. There seems to be a channeling effect between the islands that creates strong crosswinds on the bridges in particular. I’ve had to dismount and walk my bike across more than once.

Generally speaking, wind speeds above 5 m/s make cycling noticeably harder, and above 10 m/s, it becomes genuinely unsafe on the bridges. The Kurushima-Kaikyo Bridge — a series of three bridges spanning approximately 4 km in total, making it the longest crossing on the route — can be closed to cyclists and pedestrians during high winds, so please always check wind speed forecasts before heading out.

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Seasonal conditions in detail

Spring (March–May): a season of change, with May as the peak

Spring brings warming daytime temperatures and makes for a great time to cycle. March still carries lingering westerly winds and can feel chilly, but by April and especially May, conditions become much more stable and pleasant. Beyond the data, I personally feel that May is one of the most enjoyable times to ride Shimanami Kaido. Average temperature of 19.2°C (66.6°F), and 18 sunny days — among the highest of any month. The islands are wrapped in fresh greenery, and the scenery is simply stunning.

One thing to be aware of in spring is that passing low-pressure systems can bring heavy rain, even if the monthly total rainfall is relatively low. These short but heavy downpours can catch you off guard, so it’s worth keeping them in mind. Always check the forecast the evening before your ride. Also note that May includes Japan’s “Golden Week” — a cluster of national holidays in late April to early May — which means rental bikes and accommodation book up very quickly. Early reservation is strongly recommended during this period.

Summer (June–August): calm winds, but battling the heat

Summer is actually the calmest time of year in terms of wind (average wind speed 2.5 m/s). As long as a typhoon doesn’t make a direct hit, strong winds on the bridges are less of a concern. However, the biggest challenge is the heat. August averages 28.7°C (83.7°F), with daytime highs often exceeding 35°C (95°F) — which honestly makes it a tough month for beginners.

A good strategy is to set off early in the morning and take a longer break during the hottest midday hours somewhere cool. Coastal sections of the route tend to feel noticeably cooler thanks to sea breezes, so factoring those into your route planning can help.

Sun protection (sunscreen, arm sleeves, sunglasses) and regular hydration are non-negotiable. Fortunately, vending machines are plentiful throughout the islands, so picking up drinks along the way is easy.

Autumn (Sep–Nov): the season with the fewest disappointments

For first-time visitors, I most enthusiastically recommend October and November. Average temperatures are 19.6°C (67.3°F) in October and 14.1°C (57.4°F) in November — very comfortable for cycling. Both months offer around 17–18 sunny days, low rain risk, and beautifully clear air that lets you see distant islands sharply. It really is the most reliable time of year.

September overlaps with typhoon season, bringing the risk of heavy rain and strong winds arriving simultaneously — so it’s worth being prepared to adjust plans flexibly based on typhoon forecasts. By October and November, that risk drops significantly, and both rental bikes and accommodation become much easier to book.

Winter (Dec–Feb): driest months, but the windiest too

Winter is actually the driest time of year on Shimanami Kaido. January has 16 sunny days, February 15, December 16 — all surprisingly high numbers. Clear winter days offer exceptional visibility, with the islands and distant mountain ranges like the Ishizuchi massif visible with remarkable clarity.

The main challenge in winter, however, is the wind. Average wind speeds reach 3.0 m/s — the highest of any season — and persistent westerly or northwesterly seasonal winds can dominate for days at a time. On the bridges, the effect is especially harsh. If you’re cycling in winter, I strongly recommend starting from Imabari. Also keep in mind that daylight is shorter in winter, so planning with plenty of time buffer is important.

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Seasonal cycling clothing guide

Now that you have a sense of the climate, the natural next question is: “What should I actually wear?” Here’s a summary of clothing guidelines by season. You don’t need dedicated cycling apparel — outdoor sportswear works well too.

Season (Month)	Upper body	Lower body	Other tips
Spring (Mar–May)	Long-sleeve base layer + lightweight fleece or windbreaker. Layering is key as temperatures fluctuate.	Long cycling tights or lightweight pants. Three-quarter length may be enough in May.	Temperature difference between morning/evening and midday can be large. Gloves and a neck warmer are useful in March–April. Don’t forget sunscreen.
Summer (Jun–Aug)	Short-sleeve cycling jersey or moisture-wicking T-shirt. A lightweight long-sleeve UV-protection top is also effective.	Padded cycling shorts. Plain shorts are fine in July–August.	Heat protection is the top priority. Arm sleeves, sunglasses, and sunscreen are essential. Hydrate frequently.
Autumn (Sep–Nov)	Long-sleeve base layer + lightweight jersey or windbreaker. From October onward, think in layers.	Long cycling tights or full-length pants. Windproof fabrics become more comfortable from October.	Morning and evening can get chilly. A packable outer layer is very handy. Always carry rain gear.
Winter (Dec–Feb)	Insulating base layer + mid layer + windproof outer layer. Three-layer system is the standard.	Fleece-lined tights or windproof pants. Standard cycling tights alone won’t be enough.	Windproof gloves and a warm hat covering the ears are essential. On climbs your body heats up, so plan your layers to be easy to remove and put on again.

* These are general guidelines. Please adjust based on the actual temperature forecast on the day.

One thing that applies in every season is: dress in layers you can easily take on and off. Climbing a hill warms you up fast; descending the other side chills you down just as quickly. This temperature swing is something first-time cyclists often underestimate.

I learned this the hard way. One early winter day, I was sweating more than expected climbing the Miyakubo Pass on Ōshima Island. I figured I’d be fine and headed straight into the descent — and the sweat-soaked base layer turned ice-cold almost instantly. Since then, I always make a point of putting on my outer layer before descending from any pass.

Keeping a single packable jacket in your bag dramatically increases your ability to handle these temperature swings. Carrying one or two spare base layers to change into after a sweaty climb is also an effective way to manage body temperature — especially in spring, autumn, and winter.

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4 things to check the day before your ride

Checking the forecast the evening before can make a big difference to how your Shimanami Kaido ride goes. Looking at more than just “sunny or rainy?” will give you a much clearer picture.

① Precipitation probability and timing

If the chance of rain is around 30–40%, conditions are often still rideable. What matters most is when the rain is expected. If it’s forecast to clear up by mid-morning, you can simply delay your start and wait it out.

② Wind speed and direction

Weather apps and the Japan Meteorological Agency (JMA) website both provide wind speed and direction forecasts. If winds of 5 m/s or more from the west or northwest are expected, starting from Imabari puts the wind mostly at your back. Even on a sunny day, wind direction can make or break the experience.

③ High and low temperature range

In spring and autumn especially, the gap between the morning low and the afternoon high can exceed 10°C (50°F). This directly affects how you layer your clothing, so always check both the high and low temperature together.

④ Typhoon information (late August–October)

During typhoon season, start monitoring JMA typhoon updates and apps like Windy from about a week in advance. Catching the forecast early gives you enough time to consider adjusting your itinerary if needed.

For a more detailed visual wind forecast, I’d recommend the web service “Windy” (windy.com). It lets you see wind patterns displayed on an interactive map, making it easy to check conditions at specific points like the bridges. It’s widely used by cyclists around the world.

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Weather Q&A

Here are some of the most common weather-related questions I hear from readers about Shimanami Kaido.

To wrap up

In a word, Shimanami Kaido’s climate is “mild and relatively dry year-round.” Data shows roughly 280 rain-free days per year, with serious rain (ride-cancellation level) occurring only about once every 13 days. That said, each season has its own character — and knowing a little about temperature, rainfall, and wind patterns goes a long way in making your trip easier to plan. Use weather data and forecasts alongside your own preferences and physical condition to find the timing that suits you best.

One last thought: don’t chase perfect weather too hard. Even if a little rain catches you along the way, that’s just another side of Shimanami Kaido showing itself. A misty Seto Inland Sea has its own quiet beauty. Think of weather knowledge as one more tool in your travel kit — and go enjoy the ride.

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On this page, I’ve covered the weather and climate of Shimanami Kaido in detail. The route is welcoming to beginners — that’s one of its greatest strengths. For more information on cycling Shimanami Kaido, please check the page below.