The Somali Jet and India’s Monsoon Explained

The Somali Jet, also called the Findlater Jet, is a narrow, fast southwesterly air current about one to one and a half kilometres above the western Indian Ocean that crosses the equator near East Africa, races along the Somali coast and across the Arabian Sea, and delivers the moist air that feeds India’s southwest monsoon. It is one of the strongest low-level winds on Earth, with speeds that can pass 100 kilometres per hour at its core, and it blows only during the northern summer.

Few people outside meteorology have heard of it, yet the Somali Jet is part of the plumbing of the monsoon. It links the southern Indian Ocean, East African highlands, the Arabian Sea and the Indian subcontinent in one circulation, and it also drives the cold upwelling of water off Somalia and Oman. This explainer describes where the jet comes from, how it works, how it connects to Indian rainfall and what scientists still debate about its role.

Quick Facts

Key Takeaways

• The Somali Jet is a strong low-level wind that crosses the equator near East Africa and flows across the Arabian Sea towards India during the southwest monsoon, from about June to September.
• It starts in the southern Indian Ocean, where the Mascarene High pushes air north, and the East African highlands focus it into a narrow jet.
• The jet helps to carry moisture to India, and its strength varies from year to year and from week to week, in step with active and weak spells of the monsoon.
• Its winds drive strong upwelling of cold water off Somalia and Arabia, which cools the sea surface and makes the western Arabian Sea one of the most productive ocean regions.
• Much of the monsoon’s moisture also comes from evaporation over the Arabian Sea itself, so the jet is one important part of the supply chain rather than the only source.
• The Somali Jet is a lower-level jet, distinct from the upper-level Tropical Easterly Jet and the Subtropical Westerly Jet that also influence Indian weather.

What is the Somali Jet?

The Somali Jet is a concentrated stream of fast-moving air in the lower atmosphere that forms over the western Indian Ocean in the northern summer and flows from the south-west towards the Indian subcontinent. It is a jet in the meteorological sense: a narrow ribbon of air moving much faster than the air around it.

Unlike the well-known jet streams that circle the globe near the top of the troposphere, around ten to fifteen kilometres up, this jet is low, at roughly the height of a modest mountain. It is strongest over the western Arabian Sea, close to the Somali and Arabian coasts, where monthly mean wind speeds are among the highest anywhere near the surface of the tropical oceans. The wind speeds fall farther east as the jet spreads across the sea and towards India, but the flow remains strong enough to be the main low-level monsoon current over the Arabian Sea.

The jet is a seasonal feature. It emerges in late spring, strengthens quickly around the time the monsoon arrives over Kerala, peaks in July and fades in September as the monsoon retreats and the winds reverse to the winter pattern.

Why is it called the Findlater Jet?

The Somali Jet is called the Findlater Jet after Lieutenant Colonel Joe Findlater of the Royal Air Force, who identified it from low-level aircraft flights and other observations over East Africa and the Arabian Sea in the mid-1960s and published his findings at the end of that decade. Before his work, scientists knew the monsoon wind blew from the south-west but did not realise it was concentrated into a narrow, intense jet.

The discovery came during the International Indian Ocean Expedition of the early 1960s, a major scientific effort that sent ships, aircraft and instruments across the monsoon seas. Findlater’s observations showed that the winds near one kilometre above the surface were much stronger than at the surface and than in the flow just above. His name stays attached to the jet in textbooks, though it is now more often called the Somali Jet or the East African low-level jet, especially outside Britain and India.

Where does the Somali Jet begin and what is its path?

The Somali Jet begins in the southern Indian Ocean, where air flows out of the high-pressure zone of the Mascarene High near Mauritius and Madagascar, moves north-west toward East Africa, crosses the equator along the Kenyan and Somali coast and then turns right over the Arabian Sea to reach India as a south-westerly wind.

• Source region: the Mascarene High, a persistent area of high pressure over the south-western Indian Ocean during the southern winter.
• Channelling: the East African highlands, including the Kenyan and Ethiopian highlands, block the flow and funnel it into a narrow jet along the coast.
• Equatorial crossing: the air crosses the equator at around 40 to 50 degrees east, near the coast of Kenya and Somalia.
• Turn to the east: after crossing into the Northern Hemisphere, the air is deflected to the right by the Earth’s rotation and curves toward the north-east.
• Arabian Sea flight: the jet crosses the open Arabian Sea in a few days, picking up moisture and heat from the sea.
• Landfall: it arrives along India’s west coast and the peninsula as the strong south-westerly monsoon flow.

The sharp turn near the equator is the unusual part. Normally, air flowing across the equator changes direction because the Coriolis effect, which depends on latitude, reverses its sign. The mountain barrier of East Africa gives the flow a strong push along the coast as it makes this transition.

What drives the Somali Jet?

The Somali Jet is driven by the large pressure difference between the Mascarene High in the south and the heat-driven low pressure over the Asian continent, with the East African highlands and the Earth’s rotation shaping the flow into a narrow, fast current. The monsoon heating of South Asia acts as the engine.

In the northern summer, the Tibetan Plateau, the Thar Desert and the Indo-Gangetic Plain heat up intensely, and a broad zone of low pressure develops over northern India and Pakistan. Meanwhile, the southern Indian Ocean is in its winter season, with high pressure over the Mascarene region. The pressure gradient pulls air northward across the equator. The mountains of East Africa act as a wall on the western side, so the flow squeezes into a narrow strip where speeds rise sharply. This is similar to how a river speeds up through a narrow gorge.

Researchers also point to ocean-atmosphere feedback. The jet’s winds cool the sea beneath it by upwelling, which slightly lowers the evaporation and heating on the Somali side, and scientists continue to study how these feedbacks regulate the strength of the jet from year to year.

How does the Somali Jet feed India’s southwest monsoon?

The Somali Jet feeds India’s southwest monsoon by transporting warm, moist air from the western Indian Ocean across the Arabian Sea towards the west coast and peninsula, supplying a share of the water vapour that is lifted by the Western Ghats and monsoon systems to form rain. It is the fast conveyor of the monsoon flow.

The air in the jet picks up moisture as it travels over the warm sea. When the flow reaches the Western Ghats it is forced to rise, cools and condenses into heavy rain along Kerala, Karnataka, Goa and Maharashtra, while part of the moisture continues inland and across the peninsula. A stronger jet means a stronger onshore flow, more moisture transport and, on average, heavier rainfall on the west coast and central India.

It is important to describe the jet’s role carefully. Analyses of monsoon moisture show that it comes from several sources, including direct evaporation from the Arabian Sea and the Bay of Bengal, moisture carried across the equator and local recycling over land. The Somali Jet is a principal pathway for the cross-equatorial part, but the monsoon cannot be explained by the jet alone. Think of it as a major supply route within a larger system.

How is the Somali Jet linked to monsoon onset and strength?

The Somali Jet strengthens in the weeks before the monsoon reaches Kerala, which is normally around 1 June, and its strength through the season tracks active and weak phases of the monsoon, so forecasters watch it as an indicator of how vigorous the rains will be. The relationship is real but not perfectly simple.

In May, as the Mascarene High intensifies and the land heats, the cross-equatorial flow builds, and the winds over the Arabian Sea strengthen sharply. The arrival of deep, strong south-westerlies is one of the markers that the monsoon is about to set in. During the season, the jet pulses stronger and weaker over periods of a week to a few weeks, in step with the active and break spells of the monsoon. A strong jet usually goes with a vigorous west-coast monsoon, whereas a weak or disrupted jet is often found during breaks and sluggish phases.

On a seasonal scale, years with unusually strong or weak cross-equatorial flow have been associated with higher or lower rainfall, but other influences, including El Niño and La Niña in the Pacific and the Indian Ocean Dipole, also matter. Researchers therefore use the jet as one of several indicators, and not as a stand-alone predictor of the season.

How is the Somali Jet different from other jets?

The Somali Jet differs from the other jets that influence India in height, direction and season, because it is a low-level southwesterly summer jet, whereas the Tropical Easterly Jet and the Subtropical Westerly Jet blow at high altitude. The three together shape the monsoon and the winter weather.

The three jets are connected, as the monsoon onset coincides with the westerly jet shifting north of the Himalaya, the easterly jet appearing aloft and the Somali Jet strengthening at low levels.

What does the Somali Jet do to the ocean?

The Somali Jet drives intense upwelling of cold, nutrient-rich water along the coasts of Somalia and Oman, because its winds push surface water away from the coast, and deeper water rises to replace it. This cools the sea surface by several degrees and boosts marine life.

The same winds also reverse and strengthen the Somali Current, which flows northward along the African coast in summer, in the opposite direction to its winter flow, and forms large rotating features such as the Great Whirl. The result is one of the most dramatic seasonal ocean changes in the world, with a rich growth of plankton that supports fisheries in the Arabian Sea. The cold water in turn affects the atmosphere, since it reduces evaporation and slightly weakens local rainfall, and it influences which parts of the Arabian Sea supply the most moisture to the monsoon.

Ocean scientists use the upwelling record as a clue to past monsoons. Tiny shells of marine organisms in sediment cores from the Arabian Sea change with the strength of upwelling, allowing researchers to reconstruct how strong the jet and the monsoon were over thousands of years. This links the modern jet to climate history.

How do scientists observe and forecast the Somali Jet?

Scientists observe the Somali Jet with satellite scatterometers that measure ocean surface winds, moored ocean buoys, ship and aircraft measurements, weather balloons and reanalysis datasets, and they forecast it with global and regional atmosphere models. The India Meteorological Department follows the lower-level winds over the Arabian Sea daily during the monsoon.

The jet’s core lies above the surface, so winds at around 850 hectopascals, roughly 1.5 kilometres up, are the standard indicator on forecast charts. Researchers study the long-term behaviour of the jet through programmes such as research buoy arrays in the Indian Ocean and field campaigns, including those of India’s Ministry of Earth Sciences. Accurate model representation of the jet is a known challenge, because the East African highlands, the fast-changing ocean temperature and the interaction with convection all have to be captured. Errors in the jet’s strength can lead to errors in the forecast rainfall on the west coast, which is a reason for continued research.

Is climate change affecting the Somali Jet?

Climate change may be affecting the Somali Jet, but the evidence is mixed, with some studies suggesting a gradual change in the strength of the cross-equatorial flow and the Arabian Sea monsoon circulation and others finding natural variability dominates. Scientists treat the trend as an open research question.

Warming of the Indian Ocean, shifts in the land-sea temperature contrast and changes in the Mascarene High could in principle alter the pressure gradient that drives the jet. A warmer atmosphere also carries more moisture, so even an unchanged jet might transport more water vapour to India and favour intense rain. Observational records of the jet are limited to a few decades, which makes it difficult to separate a long-term trend from natural cycles such as the Indian Ocean Dipole. The prudent reading is that the jet will stay a central part of the monsoon, while its exact future behaviour remains uncertain.

Bottom Line

The Somali Jet is the monsoon’s fast, low-level supply line, a river of air that rises in the southern Indian Ocean, squeezes along the East African coast, crosses the Arabian Sea and meets the Western Ghats. It helps to deliver moisture, drives upwelling off Somalia and Oman, and gives forecasters a useful sign of how strongly the monsoon is flowing, though it is only one piece of a larger system. Last updated: 2 November 2026.

Frequently Asked Questions

What is the Somali Jet in simple words?

The Somali Jet is a fast, low-level wind that blows from the south-west across the equator near Somalia and over the Arabian Sea towards India during the summer monsoon. It carries warm, moist air that helps to bring monsoon rain to the Indian west coast.

Why is the Somali Jet also called the Findlater Jet?

It is named after Joe Findlater, a Royal Air Force officer who identified the jet from aircraft observations in the 1960s. Before that, the existence of such a narrow, intense low-level current over the Arabian Sea was not well understood.

When is the Somali Jet active?

The Somali Jet is active from about June to September, strongest around July, during the southwest monsoon. It builds in the weeks before the monsoon arrives over Kerala and weakens as the monsoon retreats and winds reverse.

How does the Somali Jet affect India’s monsoon rainfall?

It transports moist air across the Arabian Sea to the west coast and peninsula, where the Western Ghats lift it and produce heavy rain. A stronger jet generally means a more vigorous west-coast monsoon, though other factors such as El Niño also influence the season.

What is the connection between the Somali Jet and upwelling?

The jet’s winds blow parallel to the Somali and Omani coasts and push surface water offshore, so cold, nutrient-rich deep water rises to replace it. This upwelling cools the sea and supports rich marine life, and its record helps scientists reconstruct past monsoons.

How is the Somali Jet different from the Tropical Easterly Jet?

The Somali Jet is a low-level, south-westerly current about one kilometre above the sea, while the Tropical Easterly Jet is a high-altitude easterly current at around fourteen to sixteen kilometres. Both are part of the summer monsoon circulation but at very different heights.

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