Apparently there are concerns about a tropical depression that's brewing in the Atlantic and could impact the Florida crop. At last check futures were up 7.5 percent. By the way, if you never fully understood the big scene in "Trading Places" where Winthorpe and Valentine outsmart the Duke Brothers, here's a reasonable explanation. Here's another:
What Ackroyd/Murphy did was initially sell contracts for delivery at a later date. That is to say, they promised that by the delivery date they would get enough OJ by the delivery date to cover their contracts, either by obtaining the physical OJ, or by buying offsetting contracts in the market. When everybody thought there would be little OJ supply, the price of this promise to sell and deliver was very high. When everybody found out there would be ample supply, the price of this promise to deliver dropped significantly. After the price dropped, they bought back offsetting contracts for delivery (or looked at another way, they got a promise that they could buy the same amount of OJ at the delivery date that they had earlier promsed to sell). Having equalized their position, they could leave the market with the money they made.