Monsoon

The Monsoon is a Tropical Wind that changes direction every six months due to the heating or cooling of the land masses.
It affects Africa, the Indian Ocean, India and Australia. The Monsoon continually varies in rainfall, and can cause either drastic flooding or severe drought.

The Southwest Monsoon bring heavy rains to India, and then reverses direction bringing rains mainly to the east coast of India.
1. The Southwest Monsoon lasts from May to September.
2. The Northeast Monsoon lasts from October to March.

In the North Indian Ocean, comprising the Arabian Sea and the Bay of Bengal, the Cyclone Season runs from May to December.
There are two Cyclone Seasons with May and December producing the most powerful Cyclones.
1. Pre-Monsoon, April to June.
2. Post-Monsoon, October to December.
Storms do not develop into Cyclones during July and August.
The Cyclones start from Latitude 7 degrees North and track Northwest, sometimes reaching up to 30 Degrees North, their most destructive capability between 10-15 Degrees North.
Cyclones die out when they reach a landmass and usually do not occur within 5 degrees either side of the Equator.

The southwest Monsoons brought Roman ships emerging from the Red Sea to India in around 45 days.
The northeast Monsoons sent the ships home from India back to the Red Sea.

This is a 1st century CE nautical guide that describes two main sea routes using the Monsoon and was probably written by a merchant from Alexandria.
It starts at Berenice in Egypt and describes one Route via the Red Sea across to India and the Ganges, and another Route from Berenice down to the East Coast of Africa (Azania).

It was known as the ‘Hippalus’ to the Romans, and decribes the Summer Monsoon from May to September.
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.

This is also known as the Winter Monsoon and runs from 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 South West Monsoon blows during May to September or October, from the Gulf of Aden to the Andaman Sea off Thailand. The Winds are consistent and strong, blowing between Force 7 to 8, and are hot and often hold torrential rain.

The North Eastern Monsoon blows during November to March, in the reverse direction. The Wind speed is lighter blowing between Force 4 to 5. The Winds are generally cooler, drier and less consistent than the S.W. Monsoon.

The Ocean Currents in the Northern Indian Ocean, usually follow the prevailing Monsoon and are between 0.5 to 1 knot. This applies to the Somali Current, which follows and intensifies in the direction of each Monsoon.

From February to September:
- The Somali Current flows Northeastward in a band 30-60 miles (50-100km) wide, along the East Coast of Africa.
- During the Southwest Monsoon, which blows at a steady 30mph (48kph) between May and June, the Current is at its strongest flow.
- Between June and August, this intense Current produces two main Eddies that rotate clockwise, the Great Whirl and a secondary Eddy known as the Socotra Gyre.
From December to April:
- During the Northeast Monsoon, the Somali Current reverses to become a Southward Flow, reaching up to Latitude 10 degrees North, which includes most of the Somali Coastline.
- The Current is at its strongest in January. However, the current flows north between Socotra and the Horn of Africa.

From 4 to 25 degrees South, the prevailing winds are the South Eastern Trade Winds which blow all year round, at Force 4 to 5. With the exception of the Mozambique Channel where the winds increase.
The South Equatorial Current flows in a Westerly or Southwesterly direction south of the Equator at 0.5 to 1 knot.
In the South Western Indian Ocean, there are generally 8 Tropical Storms and 4 Cyclones per year.

The North Indian Ocean