Map from Google - Tokyo

In Tokyo, the Japanese capital, the climate is temperate, with fairly mild and sunny winters, and hot, humid and rainy summers. Like the rest of Japan, the city is affected by the monsoon circulation: in winter the northwest cold currents will prevail, while in summer they will be replaced by the hot and humid currents of tropical origin.
Tokyo overlooks the sea in the bay of the same name. Given the relatively low latitude (we are on the 35th parallel), and the protection of the mountains (we are on the east side), in winter the currents of Siberian origin are felt little, so there are several sunny days, and usually it's not very cold; however, cold and windy periods, with highs around 5/7 °C (41/45 °F) or less and possible snowfalls, can not be ruled out. Night frosts are rare and usually light.
In summer, hot and muggy periods (with sunshine, highs around 35 °C (95 °F), tropical nights and high air humidity) alternate with periods of bad weather, with wind and rain, and sometimes (especially in June and July) a little cool at night. August is the hottest month, both for the thermal inertia of the sea, and for the lower frequency of periods of bad weather.
Here are the average temperatures.
Average temperatures - Tokyo
TokyoJanFebMarAprMayJunJulAugSepOctNovDec
TokyoJFMAMJJASOND
Min (°C)124914182223201484
Max (°C)101014192326293127221612
Min (°F)343639485764727368574639
Max (°F)505057667379848881726154

In the western suburbs, temperatures are a bit lower, both for the greater distance from the sea, and for the lesser urban heat island effect, as you can see from the temperature of Hanno, in Saitama Prefecture.
Average temperatures - Hanno
HannoJanFebMarAprMayJunJulAugSepOctNovDec
HannoJFMAMJJASOND
Min (°C)-2-11712162021181160
Max (°C)8912172224283025191511
Min (°F)283034455461687064524332
Max (°F)464854637275828677665952

The rains are abundant, as they amount to 1,500 millimetres (60 inches) per year; winter is undoubtedly the driest season; the rainiest months are September and October, also due to the contribution made by typhoons. In August there is a certain decrease in the frequency of rains: among the summer months it is on average, as well as the hottest, the driest and sunniest.
Here is the average precipitation.
Average precipitation - Tokyo
TokyoJanFebMarAprMayJunJulAugSepOctNovDecYear
TokyoJFMAMJJASONDY
Prec. (mm)505512012514017015517021020095501530
Prec. (in)22.24.74.95.56.76.16.78.37.93.7260.2
Days5610101011108111074101

As mentioned, in late summer and early autumn, from August to October, Tokyo can be affected by typhoons, the tropical cyclones coming from the southwest, which mostly affect the southern part of the country, but can also arrive here. The most intense typhoons can bring torrential rains and heavy damage.

The cherry blossoming (Sakura) in Tokyo takes place around the 30th of March: there are dedicated events in the streets and parks where you can admire them.
Less famous but still interesting is the plum blossoming, which announces the spring, and in Tokyo occurs roughly between the 10th of February and early March. In some gardens there are festivals dedicated (matsuri ume), as in the Yushima Tenjin, near the university, or in the Yoshino Baigo of Ome, city in the metropolitan area, located near Hanno, and where the flowering occurs a little later (roughly from the 20th of February to late March).

The amount of sunshine in Tokyo is good in winter (there are no less than 6 hours of sunshine per day in December and January), while it is just mediocre or decent in the other seasons, due to spring and fall disturbances and the summer monsoon: in summer, there are only 4 hours of sunshine per day in June, 4 hours and a half hours in July and 5 and a half in August.

Tokyo

The sea is warm enough for swimming, with a temperature of 23 °C (73 °F) or more, from July to October, as you can see in the following table.
Sea temperature - Tokyo
TokyoJanFebMarAprMayJunJulAugSepOctNovDec
TokyoJFMAMJJASOND
Sea (°C)171616172022242625232119
Sea (°F)636161636872757977737066