The humid, heavy air of this time of year can make one feel a bit reluctant to head outdoors, but once you start riding and approach the mountains, your spirits begin to lift. As you gradually gain altitude, the air turns cool and refreshing. By the time you reach the summit of a mountain pass, you'll have consumed a lot of fluids and will likely be feeling the fatigue, but you'll also gain a sense of satisfaction that outweighs it all.
It would be unbearable if days like this lasted all year round, but when you consider that this is only a brief period within the year, it becomes something you can actually enjoy. Of course, you’ll often get rained on, but you might even find that to be a pleasant and enjoyable experience. (Though it can be quite disheartening if it's too intense. Or perhaps there are even some people who get a little too excited by it...)
That said, heading out without any gear at all won't be very fun, so I recommend bringing along a highly water-resistant vest for such times.
Depending on how you ride, if you're hitting the road hard in a cycling jersey and bib shorts, wearing a standard long-sleeved rain jacket can turn into a sauna once your body temperature rises, making it unbearable to keep on. On the other hand, if you wear nothing at all, your body will steadily get cold. In such cases, a vest that protects your core is just right. Of course, your arms will get wet, and over time your core will get damp as well, but that just feels about right.
During this time of year, one item I use frequently is the S1-V Riding Vest from Search and State.
Search and State
S1-V Riding Vest
¥29,500 (excl. tax)
This riding vest uses fabric with high water resistance and breathability. The use of a double zipper is also a major highlight; it allows for efficient ventilation in this vest, which lacks dedicated vents, and makes accessing your jersey's back pockets smooth and easy. Of course, it is also equipped with a pocket featuring a water-resistant zipper, which is very useful, but I recommend moving your essentials to your cycling jersey pockets if the rain starts to get heavy, as water will eventually seep in.
Here is another vest I recommend.
7mesh
Resistance Vest
¥27,000 (excl. tax)
Color: Ember (Orange), 2 Ball Blue (Blue)
This vest, which utilizes Gore-Tex® Windstopper®, actually possesses high water resistance. It is not completely waterproof, of course, but it is a vest that serves well during the rainy season or on rainy rides in the middle of summer. The back panel uses a breathable and stretchy fabric; while rain will enter through this area, it helps to keep your overheated body appropriately cooled down.
Both offer high water resistance, but neither is designed to be completely waterproof. However, they are highly effective items for riding on rainy days starting from this time of year.
If you want to enjoy riding during the rainy season, I highly recommend trying out this style.