In New Delhi, capital of India, the climate is subtropical, with a very mild and sunny winter, a pre-monsoonal very hot season from mid-March to mid-June, and a muggy and rainy summer, due to the monsoon.
Here are the average temperatures.

Rainfall amounts to about 800 millimetres (31.5 inches) per year, but from October to May it rains very rarely. Here is the 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.

Due to the northern location, winter here is not as warm as in other parts of India: in January, lows are around 6 °C (43 °F), but sometimes they can 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 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 gusts of wind.
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 the summer monsoon season. The rains are abundant also in August, and to a lesser extent in September.
In October, after the monsoon, the sun shines again steadily; the night temperature drops below 20 °C (68 °F), but during the day it's still hot, although the air is drier, therefore more bearable. In November, the heat becomes acceptable, with highs around 28 °C (82 °F), and cool night-time temperatures. December is by now a winter month, and it is almost as cool as January.

When to go

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