Cyclone Risk for Any Plot in India

Recorded cyclone exposure, the IS 875 (Part 3) design wind zone, and every tropical cyclone logged within 100 km — from IMD / RSMC New Delhi best-track records going back to 1842.

What cyclone risk means for a plot — and what it does not

India has the longest cyclone-exposed coastline of any country in the Indian Ocean region. For land, cyclone risk resolves into three separate questions: how often storms have actually passed this location, what wind speed the building code makes you design for, and what that combination does to construction and insurance cost.

Exposure is history, not forecast

Everything in this tool is a record. The India Meteorological Department, as the Regional Specialised Meteorological Centre for the North Indian Ocean, maintains best-track archives of tropical cyclones going back to 1842. Counting how many of those tracks passed within 100 km of a plot tells you whether it sits on a recurring storm corridor. It tells you nothing about next season.

The design wind speed is the number that costs money

IS 875 (Part 3) assigns a basic wind speed to every part of India, from 33 m/s inland to 55 m/s on the most exposed coasts. That figure is a legal input to structural design: it sets roof anchorage, cladding fixings and the lateral load case. Two otherwise identical plots in different zones do not cost the same to build on, and that gap is knowable before you buy.

India’s recorded cyclone exposure

The map below is a historical cyclone-exposure surface: for every point in India it measures the intensity-weighted density of tropical-cyclone tracks that have passed nearby across the recorded best-track history (IMD / RSMC New Delhi, 1842 to present). It is coastal-concentrated — the east coast reads High to Very High, the Arabian-Sea west coast lower, and the deep interior Negligible. Your plot’s class on this surface is what drives the tool’s verdict.

Map of India shaded by historical tropical-cyclone exposure. Very High and High exposure hug the Bay of Bengal east coast — Odisha, coastal Andhra Pradesh, Tamil Nadu and West Bengal. The Arabian-Sea west coast (Gujarat, Maharashtra, Kerala) reads Low to Moderate. The Deccan interior, north-west and Himalaya read Negligible. — India — Historical Cyclone ExposureIntensity-weighted density of recorded tropical-cyclone tracks (IMD / IBTrACS North Indian Ocean best tracks), weighted by each fix’s wind. A descriptive activity map — not an official regulatory hazard zonation.

Why the Bay of Bengal dominates

The Bay of Bengal produces roughly four cyclones for every one in the Arabian Sea, and its shallow, narrowing northern end amplifies storm surge far beyond what the same wind speed would produce elsewhere. Odisha, Andhra Pradesh, West Bengal and coastal Tamil Nadu carry India’s highest recorded exposure. The Gujarat and Konkan coasts are genuinely exposed but less frequently; the interior Deccan mostly sees remnant rain rather than damaging wind.

What do these numbers mean?

The result card separates what has been recorded from what the code requires. Here is how to read each part.

Cyclone Exposure Class

Where this location sits on the recorded-exposure scale, derived from the density and intensity of cyclone tracks that have passed nearby. When the exposure layer is unavailable the card says so rather than defaulting to a low class.

Reading guide: This is a descriptive, intensity-weighted density of recorded tracks — not a probability and not a return period.

IS 875 (Part 3) Wind Zone

The basic wind speed the National Building Code assigns here, in m/s. Your structural engineer designs to this number, so it is a direct input to the build budget rather than a risk score.

Why it matters: 33 m/s inland versus 50 m/s on an exposed coast is a real difference in structural steel, anchorage and cladding cost.

Recorded Storm History (100 km)

How many tropical cyclones in the IMD best-track archive have passed within 100 km, with an activity level summarising the frequency. The long record is the point: it captures corridors a recent decade would miss.

Example: “75 tropical cyclones within 100 km” counts passages since 1842, one entry per storm — not landfalls, and not hits on the plot.

Coastal Distance Context

Cyclone wind decays quickly inland, while surge is confined to low-lying coastal strips. Distance from the coast is what separates a wind-design problem from a surge-and-clearance problem.

What to check next: Within CRZ limits, clearance under the Coastal Regulation Zone notification applies on top of anything cyclone-related.

How the analysis works

Two independent sources: a recorded-track archive and a national design standard.

You mark the site

Draw the plot boundary, drop a pin, or type an address. Cyclone exposure varies over tens of kilometres, so the centroid is what the reading uses — the polygon shape matters far less than the location.

We search the IMD best-track archive

Every tropical cyclone track recorded in the North Indian Ocean since 1842 is checked against a 100 km radius around your plot. Passages are counted once per storm and summarised into an activity level.

We read the IS 875 wind zone

The basic wind speed for the location comes from the IS 875 (Part 3) zone map — the same figure a structural engineer designs to. It is reported alongside the history rather than blended into it, because one is a record and the other is a requirement.

Methodology and data sources

Recorded tracks from IMD / RSMC New Delhi; design wind speed from IS 875 (Part 3). Neither is a forecast.

Cyclone history: IMD / RSMC New Delhi best tracks

The India Meteorological Department, acting as the Regional Specialised Meteorological Centre for the North Indian Ocean, maintains the authoritative best-track archive of tropical cyclones in the Bay of Bengal and Arabian Sea. Best tracks are the post-season reanalysis of each storm’s position and intensity — more accurate than the operational advisories issued at the time. We count tracks passing within 100 km of the plot, once per storm.

IMD / RSMC New Delhi best tracks1842 – present100 km search radius

Design wind speed: IS 875 (Part 3)

IS 875 (Part 3) is the Indian standard for wind loads on buildings and structures. It divides India into basic wind speed zones from 33 m/s to 55 m/s, and that figure is a legal input to structural design. It is reported here unchanged, not combined with the exposure class.

IS 875 (Part 3)33–55 m/s basic wind speed

Limitations

Not a forecast. Every number is a record of past storms or a code requirement. Nothing here estimates the probability of a cyclone in any future period.
Exposure is descriptive. The exposure class is an intensity-weighted density of recorded tracks. It is not a return period, not an annual probability, and not an insurance rating.
Passages, not impacts. A track within 100 km is not damage at the plot. Actual impact depends on intensity at closest approach, storm size, terrain and surge exposure.
Storm surge is not modelled. Surge risk depends on coastal bathymetry and local elevation, neither of which this tool reads. For a low-lying coastal plot, commission a surge study.
Exposure may be unavailable. The exposure raster is deployed separately from the track archive. Where it is missing, the report says so and still reports history and wind zone — a missing class is never shown as low risk.

Frequently Asked Questions

Is this a forecast?

No. Nothing here predicts a future storm. Every figure is a record of what has already happened — the tracks of tropical cyclones logged by the India Meteorological Department since 1842 — plus the design wind speed the National Building Code assigns to that location. Treat it as exposure history and a construction input, not a warning.

What is the IS 875 (Part 3) wind zone?

IS 875 (Part 3) is the Indian standard for wind loads on buildings. It divides the country into basic wind speed zones from 33 m/s up to 55 m/s. Your structural engineer designs to that speed — it drives roof anchorage, cladding fixings and the lateral load case. A coastal plot in a 50 m/s zone costs measurably more to build to code than an inland plot at 39 m/s, and that difference belongs in the budget before you buy.

What does the cyclone count within 100 km actually mean?

It is how many tropical cyclone tracks in the IMD best-track archive have passed within 100 km of your plot since records began. It counts passages, not landfalls, and a single storm is counted once. A high count means the location sits on a recurring storm corridor; it does not mean the plot has been hit.

Why does the east coast score so much higher than the west?

The Bay of Bengal generates roughly four times as many tropical cyclones as the Arabian Sea, and its shallow, funnel-shaped northern end drives far higher storm surge. Andhra Pradesh, Odisha, West Bengal and Tamil Nadu therefore carry the highest recorded exposure in India. The Gujarat and Maharashtra coasts are exposed but less frequently, and the interior Deccan sees remnants as rain rather than damaging wind.

Does a high exposure class make land unbuildable?

No. Most of India's coastal economy sits in high-exposure districts. It changes what compliant construction costs and what insurance costs — higher design wind speed, better anchorage detailing, and in CRZ areas an additional clearance regime. It is a cost and design input, not a disqualification.

Why might the exposure class come back unavailable?

The exposure layer is a separate raster from the best-track history. When it has not been deployed for your location the report says so plainly and still shows the recorded storm history and the design wind zone, which are the parts that come straight from the IMD archive and the IS 875 map. A missing exposure class is never reported as low risk.