Map from Google - Hamamatsu

In Hamamatsu the climate is temperate, with quite 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.
Hamamatsu is located in the central part of Honshu, on the coast, in the Shizuoka prefecture. North of the city lie the Kiso Mountains, or Central Alps, with a series of peaks almost 3,000 metres (9,800 ft) tall.
Given the relatively low latitude (we are on the 34th 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 several sunny days, and usually it's not very cold; however, cold and windy periods, with highs around 6/8 °C (43/46 °F) or less, can not be ruled out. Snowfall is very rare: unlike in Tokyo, where sometimes it can snow, here in practice it never snows (but sometimes it can snow on the northern outskirts of the city, see Tenryu-ku). Night frosts are quite rare and usually light, however, at night the temperature often drops close to 0 °C (32 °F).
In summer, hot and muggy periods alternate with periods of bad weather, with wind and rain. Fortunately, the breeze blows from the sea.
Here are the average temperatures.
Average temperatures - Hamamatsu
HamamatsuJanFebMarAprMayJunJulAugSepOctNovDec
HamamatsuJFMAMJJASOND
Min (°C)23610151923242115105
Max (°C)101114192326293128231813
Min (°F)363743505966737570595041
Max (°F)505257667379848882736455

In Hamamatsu precipitation is abundant, given that it amounts to 1,800 millimetres (70 inches) per year. The driest season is definitely the winter. The rainiest periods are the first part of the rainy season (mid-June to mid-July, the plum rains), and the latest (September, also due to the contribution made by typhoons, see below).
Here is the average precipitation.
Average precipitation - Hamamatsu
HamamatsuJanFebMarAprMayJunJulAugSepOctNovDecYear
HamamatsuJFMAMJJASONDY
Prec. (mm)5580150165190240190150250165120501810
Prec. (in)2.23.15.96.57.59.47.55.99.86.54.7271.3
Days

In late summer and early autumn, from August to October, Hamamatsu can be affected by typhoons, tropical cyclones, which in this area, facing south, are felt in a particular way. The most intense typhoons can bring torrential rains and heavy damage.
The cherry blossoming in Hamamatsu takes place around the 30th of March.
The amount of sunshine in Hamamatsu is good in winter (there are more 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 to the summer monsoon. In summer, August is the sunniest month: apart from typhoons and some waves of bad weather, there are several sunny periods.

Hamamatsu

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 - Hamamatsu
HamamatsuJanFebMarAprMayJunJulAugSepOctNovDec
HamamatsuJFMAMJJASOND
Sea (°C)171616172022242625232119
Sea (°F)636161636872757977737066