Honshu, map

In Shizuoka, the climate is temperate, with mild, 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 hot and humid currents of tropical origin.
Shizuoka is located in the central part of Honshu island, halfway between Nagoya and Tokyo, and on the coast, in Suruga Bay, an area particularly exposed to the summer monsoon. North of the city lie the Akaishi Mountains, or Southern Alps, with a series of peaks around 3,000 meters (9,800 ft) high and some winter resorts, while to the north-east lies Mount Fuji.
Because of both the relatively low latitude (we are on the 35th parallel) and the protection of the mountains (we are on the southern side), in winter, the currents of Siberian origin are felt little, so there are many sunny days, and usually, it's not very cold. However, cold and windy periods, with highs around 7/10 °C (45/50 °F) or less, can not be ruled out. Snowfall is very rare: unlike in Tokyo, where it can sometimes snow, here, in practice it never snows. Night frosts are rare and usually light.
Although it rarely rains in winter, given the exposure to the southern winds, when it rains, it can rain a lot.
In summer, sunny and muggy periods alternate with periods of bad weather, with wind and rain.
Here are the average temperatures.
Shizuoka - Average temperatures
Min (°C)2261015192324211594
Max (°C)121215202326303128231814
Min (°F)363643505966737570594839
Max (°F)545459687379868882736457

Precipitation in Shizuoka is definitely abundant, around 2,300 millimeters (90 inches) per year, so much so that it is one of the rainiest cities in Japan (together with some cities on the northern side of Honshu island, such as Kanazawa and Komatsu). Winter is definitely the driest season; in summer, from June to September, more than 1,100 millimeters (43 inches) of rain fall.
Here is the average precipitation.
Shizuoka - Average precipitation

From June to October (but especially from August to early October), Shizuoka can be affected by typhoons, the tropical cyclones of the western Pacific, which in this area, facing south, are felt in a particular way. The most intense typhoons can bring torrential rainfall and heavy damage.
The cherry blossoming in Shizuoka takes place around March 30th.
The amount of sunshine in Shizuoka is good in winter (there are almost 7 hours of sunshine per day in December and January), while it is just mediocre or decent in the other seasons because of the disturbances that occur in spring and autumn, as well as the monsoon in summer. However, August is the sunniest month of summer. Here are the average sunshine hours per day.
Shizuoka - Sunshine

Mount Fuji from Shizuoka

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.
Shizuoka - Sea temperature
Temp (°C)171616172022242625232119
Temp (°F)636161636872757977737066