Map from Google - New_Delhi

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

Rainfall amounts to about 800 mm (31.5 in) per year, but from October to May it rains very rarely. Here is the average precipitation.
Average precipitation - New Delhi
New DelhiJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec. (mm)20151030305522025013515715802
Prec. (in)

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 the occasional disturbances, are rare. Already in February the temperature increases, by a few degrees, and already in March it's practically summer, since the maximum temperatures are around 30 °C (86 °F).
In April, the heat becomes oppressive, with an average of 36 °C (97 °F), but in the course of the month the temperature 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). In the second half of June, the temperature drops a bit and the first rains occur.
In July, the temperature decreases, dropping to about 35 °C (95 °F), and the heavy rains finally arrive: during the month, more than 200 mm (8 in) of rain fall; on the other hand, however, 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 even in the summer monsoonal 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 night-time temperatures getting cool. December is by now a winter-like month, and it is almost as cool as January.

New Delhi, Lotus Temple

When to go

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