# Calculation method

Hello! Thank you for your interest in learning more about how we calculate wind speeds.

Note: It is not a requirement to understand this process to receive your payout. This calculation is executed automatically on your behalf. This page is only for those interested in the science behind the product; for fellow science geeks like us. 😉

A policy pays according to the highest wind speeds calculated over land within 25 miles of a location. The location of a microinsurance policy is the center of your municipality.

So how do we calculate wind speeds?

To calculate the highest wind speeds for a given location, we first need to calculate the wind speeds across all of Puerto Rico for that event.

The first step is to download the hurricane track dataset from NOAA's National Hurricane Center (NHC). (https://ftp.nhc.noaa.gov/atcf/btk/) The track data sets contain the exact positions (latitude and longitude) of the tropical cyclone, the associated time (usually in UTC), the 1-minute sustained wind speeds (in knots), the central and sea level pressure (in millibar) and the radius of maximum wind speed (Rmw - in nautical miles) at any given time.

This dataset is downloaded and reviewed for quality once the NHC publishes a track point for an event that has entered the vicinity of Puerto Rico and left it. This vicinity is defined by a 1.5 degree bounding box around Puerto Rico.

To simplify the calculations over Puerto Rico, we discretize Puerto Rico into 2786 individual points and use a roughness coefficient to account for the topography of the island.

Applied Wind Field Model

We calculate the wind speeds for all of 2786 points by using the wind field method proposed by Holland (1980) and adjust for roughness along the whole track of the tropical cyclone within the bounding box around the island.

All discrete points that fall within 25 miles (40.2340 km) of the municipality center are searched for and compared. The highest calculated wind speed value from all of these discrete points is used to determine the payout for the given municipality.

Historical examples

These are a couple of historical examples of calculated wind speeds using this method. The “hexes” seen on the map are a visual representation of these points. The color is the threshold that the wind speeds fall into in regards to our payout table:

For any questions or feedback please send us an email to support@getraincoat.com.