New Delhi, where it is

In New Delhi, the capital of India, the climate is subtropical, with a very mild and sunny winter, a very hot season from mid-March to mid-June (before the monsoon), and a muggy and rainy summer due to the monsoon.
Here are the average temperatures.
New Delhi - Average temperatures
Min (°C)6101420262827262418117
Max (°C)212429364039353434342823
Min (°F)435057687982817975645245
Max (°F)70758497104102959393938273

Rainfall amounts to about 800 millimeters (31.5 inches) per year, but it rains very rarely from October to May. Here is the average precipitation.
New Delhi - Average precipitation

The sun in New Delhi often shines in the dry season, while in the rainy season, the sunshine hours decrease a bit, though not as much as in other areas of India. Here are the average sunshine hours per day.
New Delhi - Sunshine

Owing to the northern location, the winter here is not as warm as in other parts of India: in January, lows are around 6 °C (43 °F), but they can sometimes approach freezing (0 °C or 32 °F). During the day, however, the temperature is pleasant: the average maximum is 21 °C (70 °F). The sun often shines, and the rains, brought by occasional disturbances, are rare. Already in February, the temperature increases by a few degrees, and by March, it's practically summer, since the maximum temperatures are around 30 °C (86 °F).
In April, the heat becomes oppressive, in fact, the daytime temperature is on average about 36 °C (97 °F), but in the course of the month, it can easily exceed 40 °C (104 °F). In May and June, temperatures about 40 °C (104 °F) are the norm, but sometimes, they can reach 46/47 °C (115/117 °F). During this very hot period, rare thunderstorms can occur, accompanied by wind gusts.
In the second half of June, the temperature drops a bit and the first rains due to the monsoon occur. In July, the temperature decreases, dropping to about 35 °C (95 °F), and heavy rains finally arrive: during the month, more than 200 mm (8 in) of rain fall; on the other hand, relative humidity increases, and at night, the temperature remains high, around 26/27 °C (79/81 °F). However, the rains in this area of India are intermittent, and there may be very hot and sunny periods also in mid-summer. The rains are still abundant in August, and to a lesser extent in September.
In October, after the monsoon, the sun shines steadily again; the night temperature drops below 20 °C (68 °F), but it's still hot during the day, although the air is drier, and therefore the heat is more bearable. In November, the heat becomes acceptable, with highs around 28 °C (82 °F) and cool night-time temperatures. By December, it is winter, and it is almost as cool as in January.

New Delhi, Lotus Temple

Best Time

The best time to visit New Delhi is from November to February, in order to avoid both the heat of the period from March to June (which partially returns in October) and the rains of the period from July to September.