Tokyo's weather isn't 23 separate forecasts. It's one system with 23 expressions.

Why These Six Nodes

We didn't pick Shinjuku, Shinagawa, Taito, Setagaya, Koto, and Nerima because they're famous. We picked them because they're where the climate system bends. Each one sits at a pressure point where two or more weather forces collide, and that collision sends ripples through the entire network.

Shinjuku is the heat engine. Its skyscrapers compress warm air, its asphalt stores solar energy through the afternoon, and its air conditioning exhaust adds a secondary heat source that most forecasts ignore. On a clear August day, Shinjuku runs 2-3 degrees Celsius hotter than the JMA reading for "central Tokyo." That heat doesn't stay put. It radiates outward in four directions, and the path it takes determines who gets a hot evening and who gets a break.

Shinagawa is where the bay breeze makes first landfall. If you cycle south from Shibuya at 11am, you'll feel the temperature drop between Gotanda and Osaki. That's not shade. That's the sea breeze front arriving from Tokyo Bay, and Shinagawa is the station where it docks. The timing varies by 20-40 minutes depending on the overnight cooling and the pressure gradient, but it almost always arrives. What changes is how far inland it gets.

Taito sits on the Sumida River corridor. The river creates a wind channel that runs north-south through the eastern wards, and Taito is where that channel starts to matter. Morning fog rides this corridor down from Adachi and Katsushika. Evening wind rides it back up. If you've ever wondered why Asakusa feels different from Ueno despite being the same distance from the bay, the Sumida River is your answer.

Setagaya is the absorber. Heat flows west from Shinjuku across the residential grid of Shibuya Ward and into Setagaya's tree-lined streets. But Setagaya doesn't just take the heat. Its green spaces — Komazawa Olympic Park, the Tama River banks, the pocket gardens between houses — buffer the temperature rise. A cyclist heading west from Shinjuku at 7pm will feel a 3 degree drop by the time they reach Sangenjaya. That's not elevation. That's Setagaya doing its job.

Koto is where the heat goes to die. The bay water here is shallow and warms quickly, but it still absorbs thermal energy from the inland wards. Koto's flat terrain creates an escape route for hot air that piled up in Shinjuku and Chiyoda during the day. At night, this eastward flow is visible on thermal satellite images — a warm plume extending from central Tokyo out over the bay. Koto sits in the middle of that plume.

Nerima is the edge. It's the westernmost of the 23 wards, and it feels the outside weather first. Cold dry air from the Tama River gap hits Nerima before it reaches anywhere else. Warm air from the city basin sometimes pools here when it's blocked by the Mejirodai ridge. Nerima is where Tokyo's weather system connects to the larger system beyond the mountains, and that connection matters more than most people realize.

How the Network Works

The fifteen lines connecting these six nodes aren't decorative. Each line's thickness shows the current temperature difference between two districts. A thick red line means a large gap — one node is baking while the other stays cool. A thin lavender line means the two districts are in thermal equilibrium, sharing the same air mass.

The colors follow the same logic. Lavender links are weak — the temperature difference is under 2 degrees Celsius, meaning the two districts are essentially experiencing the same conditions. Amber links are moderate — 2 to 4 degrees of separation, enough that you'd notice it if you cycled between them. Red links are strong — more than 4 degrees, a significant climate break that shapes local wind patterns and human comfort.

These links change throughout the day. The Shinjuku-to-Koto link is typically strongest at 9pm, when the heat island has peaked and the bay is still absorbing. The Shinagawa-to-Taito link strengthens in the early afternoon as the bay breeze pushes inland. The Nerima-to-Setagaya link is often strongest in the morning, when cold air from the Tama River gap is still draining eastward before the sun warms it.

We update the network every time you load the page, pulling fresh data from the Open-Meteo API for each node's precise coordinates. No averages. No interpolations. Six actual points in space, connected by the temperature differences that matter.

What You'll Find Here

Tenki Link is a field guide to Tokyo's climate system, written for people who move through the city and feel the shifts. We cover four main pathways that connect the districts:

Heat Flow tracks how warmth moves through the urban fabric. Shinjuku generates it. Setagaya absorbs it. Koto releases it to the bay. And Nerima gets blocked from receiving it by a ridge most people have never heard of. If you've ever wondered why your evening bike commute gets cooler or hotter depending on which way you turn, this is your map.

Bay Breeze follows the sea breeze from Tokyo Bay inland. It hits Shinagawa first, weakens as it pushes toward Chiyoda, and rarely makes it past Shinjuku. But on strong-gradient days, it surprises everyone by reaching Nakano. Understanding the bay breeze's daily schedule is one of the most practical climate skills a Tokyo cyclist or commuter can develop.

River Corridors explores how the Sumida, Tama, Meguro, and Kanda Rivers create wind and temperature channels that link otherwise separate districts. The Sumida corridor is the most dramatic — a north-south highway for air that you can feel from a bicycle. The Tama River delivers the freshest air entering Tokyo from the west. And the Meguro River explains why Nakameguro is cooler than Ebisu despite being only 500 meters away.

Mountain Gap looks at how Tokyo's mountain ring connects the city to the larger weather system. Cold air enters through the Tama River gap. Thunderstorms approach through the Iruma Valley. And on certain wind days, warm city air escapes through tunnels under the terrain that most residents don't know exist. This is where Tokyo's microclimates meet the macroclimate.

Who This Is For

We built Tenki Link for systems thinkers who got tired of checking a single "Tokyo" forecast and discovering it had nothing to do with the weather they were actually experiencing. For cyclists who plan routes around temperature gradients. For commuters who've noticed that the walk from the train station feels different in summer depending on which exit they take. For urban planners who know that asphalt ratios matter more than most zoning codes acknowledge.

If you've ever stood on a street corner in Shinjuku at 8pm and felt a wall of warm air hit your face, then turned a corner and felt it disappear, you already understand what we're mapping. We're just giving you the vocabulary and the data to track it systematically.

The network above is live. The essays are permanent. Together, they form a picture of Tokyo that no single weather app can show you — because no single weather app treats the city as a connected system. We do.