Will NYC have more than 6 inches of precipitation in September?

This market resolves on actual precipitation in New York City during September: "Yes" means more than 6 inches (152 mm) falls in total. The current 3% price looks unjustifiably low. September is climatologically one of NYC's wettest months, with a normal around 4.3-4.5 inches, but the distribution is strongly right-skewed: individual years deliver 8-12 inches or more.

Our model puts the probability of exceeding 6 inches at 16%. That is based on historical frequency: over recent decades roughly 15-20% of Septembers recorded more than 6 inches in Central Park. In addition, a warm Atlantic and residual tropical systems raise the risk of extreme rainfall precisely in September, fattening the tail. The market appears anchored to the "average" scenario and ignores the asymmetry.

For "Yes" to win, one or two heavy events suffice: a tropical storm, a slow-moving front, or a series of thunderstorms. Risks to our estimate are a dry blocking anticyclone that persists all month, or storm tracks shifting away. If the forecast for the first half of September is persistently dry, the probability could fall below 10%, and the bet would lose its rationale.