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Monsoon onset and seasonal rainfall markets

The South Asian monsoon affects crops, food prices, power demand and the lives of more than a billion people. Event contracts ask when the monsoon will reach Kerala, whether seasonal rainfall will be above normal, or whether a city will get a certain amount of rain in a month. Each depends on an official declaration or dataset with its own rules. This SoftCta guide covers how those sources work.

Onset is a declaration

The India Meteorological Department, or IMD, declares the onset over Kerala when rainfall at a set of listed stations, wind conditions and cloud indicators meet published criteria. The normal date is around June 1, with a spread of about a week either way. A contract on onset by a date settles on the IMD declaration, not on media reports of heavy rain.

Percent of long period average

IMD reports June to September seasonal rainfall for the country as a percentage of the long period average. Categories such as deficient, below normal, normal, above normal and excess are defined by ranges. A contract on normal rainfall should name the category boundaries and the final seasonal statement that settles it.

Regional and station totals

National totals can hide large regional differences. IMD reports subdivision and district totals, and city stations record their own amounts. Station data can be revised after quality checks. Our weather verification guide explains why station choice and data vintage matter.

Forecasts versus outcomes

IMD issues long-range forecasts in April and an update in late May or June. A forecast of normal rainfall is not an outcome. Our El Niño guide covers one of the large-scale drivers that forecasters watch, and why its link to the monsoon is real but loose.

Timing and time zones

IMD bulletins are issued on India Standard Time. A by-date contract needs a clear time zone. See our timezone guide for how venues handle cutoffs.

Drought and other regions

A weak monsoon can trigger drought declarations, which are separate events; our drought monitor guide covers US-style indices. Other monsoon systems in East Asia, West Africa and North America have their own agencies and definitions.

A simple reading habit

Write down the agency, the exact product named in the rules and the date it is published. Note the climatological normal and spread for the event. Then compare the market price with that spread and with the latest official forecast, keeping in mind that forecasts carry wide uncertainty.

Primary sources SoftCta readers open

• India Meteorological Department monsoon onset bulletins, press releases and end-of-season reports.
• IMD long-range forecast statements.
• The venue rulebook naming the declaration, dataset and deadline.

Reading the quote step by step

• Read the full title and rules, including the named settlement source and the time zone.
• Convert the Yes and No prices to implied probabilities and note the gap between them.
• Subtract fees and spread to see the effective price you would actually face.
• Write your own probability range and the evidence behind it, then compare.
• Check related and near-duplicate markets on other venues for consistency.

Closing SoftCta checklist

• Re-read the venue definition in your own words before reacting to a price.
• Convert prices with fee and spread awareness; verify live cents on the operator.
• Prefer primary settlement sources over secondary headlines and social summaries.
• Treat ChanceWire hubs, movers, and tools as orientation — not order entry.
• Confirm age, location, and product eligibility; SoftCta pages will not suggest location spoofing.
• If clarity is incomplete, watching is a complete SoftCta outcome — no pick-selling urgency required.

SoftCta habits

• Write your own probability range before checking the crowd price.
• Prefer dated primary sources over social summaries.
• Compare related markets when a single book looks extreme.
• Size curiosity with fees and depth in mind; substantial risk of loss.