(Bloomberg) -- Cocoa futures in New York saw the largest price drop in records going back more than 60 years, with a forecast of wetter weather for key producers feeding further volatility to the market.

The most-active contract in New York fell as much as 19% on Monday, while London futures fell as much as 18%. Rainfall is boosting the outlook for crops, and low open interest in cocoa markets is amplifying price moves.

Rains “should improve conditions quite a bit” in Ghana, the world’s second-biggest grower, and Indonesia, Donald Keeney, senior meteorologist at Maxar Technologies Inc., said in an email. Top producer Ivory Coast will also benefit from wet weather, said Keeney, but still needs more rainfall to completely end the dryness stressing crops. 

In Ghana, the combination of rain and sunshine has been good for cocoa, and growers would like the pattern to continue, said Michael Acheampong, a chief farmer in the town of Kwarbeng about 100 kilometers (62 miles) north of Accra.

Low open interest means that “the tiniest updates to weather forecasts in West Africa or signs of demand destruction will cause these big price swings,” said John Goodwin, a senior commodity analyst at ArrowStream Inc.

A lack of moisture in top West African cocoa producers has weighed on supply in a market already hit by aging trees and disease. Prices saw a 9% recovery last week, with money managers boosting their net-bullish bets to a three-week high. Still, some expect that a record price set in mid-April will mark the peak of the historic rally.

--With assistance from Ekow Dontoh, Tolani Awere, Pius Lukong and Baudelaire Mieu.

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