Hippalus

The Hippalus is the name for the Monsoon Wind which according to Pliny the Elder was named after Hippalus, the Greek Navigator who discovered it.

The Southwest Monsoon (Summer Monsoon – May to September).
- The Southwest Monsoon was known as the ‘Hippalus’ to the Romans.
- It collects moisture over the Arabian Sea and reaches India where it ‘bursts’ over the western coast around the first of June, covering all of India by around the 15th July. It then starts to leave India from the 1st of September and has left by the 1st of October.
- The winds blow from the Indian Ocean onto the western coast of India and Sri Lanka.
- When they reach the Western Ghats mountain range, their moisture is released as a continuous downpour over India.
- The Himalayas force the Monsoon Winds to release their moisture, and block them from reaching China.
The Northeast Monsoon or ‘Retreating Monsoon’ (Winter Monsoon – December to March).
- As the Indian subcontinent cools in September, cool air is drawn back in the reverse direction.
- This is known as the Northeast Monsoon, which reverses direction and collects moisture over the Bay of Bengal. It usually ‘bursts’ over the eastern coast of India around the 20th of October, lasting up until the 10th of December.
- The winds blow over the Eastern Ghats mountain range, but only the Monsoon that has passed over the Bay of Bengal picks up moisture, and only Andhra Pradesh and Tamil Nadu receive rain during the winter.

The Monsoon continually varies in rainfall, and can cause either drastic flooding or severe drought.

The Periplus of the Erythraean Sea describes two sea routes in the Indian Ocean using the Monsoon during the 1st century CE. It was probably written by a Merchant from Alexandria.
1. It starts at Berenice in Egypt and describes the route down the Red Sea and across to India and the Ganges.
2. It also describes another Route from Berenice down the East Coast of Africa known as Azania, to Rhapta.