NEW DELHI - The monsoon has retreated from India, the national weather office said on Thursday, after summer rains started withdrawing from the northwest of the country late last month, more than a week later than normal.

Monsoon rains were 6% below average this year, according to the India Meteorological Department (IMD), the lowest rainfall since 2018.

Monsoon is critical for India, one of the world's top producers of staples such as rice, wheat and sugar, as nearly half of India's farmland lacks irrigation.

The IMD defines average, or normal, rainfall as ranging between 96% and 104% of the 50-year average of 87 cm (35 inches) for the season.

With a weak start, monsoon rains were 9% below average in June before rebounding to 13% above average in July. The monsoon was patchy again in August, with the weather office registering 36% below average rains during the month - the driest on record.

Rains revived again in September, when India received 13% above average rains, leading to a narrower rainfall deficit.

(Reporting by Mayank Bhardwaj; Editing by Susan Fenton)