Low commodity prices, a drought at home and Venezuela's economic crisis have created a cash shortage for Cuba's Communist government, restricting its ability to trade just as it could be taking advantage of an economic opening with the United States.

我认为，句中的as 表示时间，just as 意为“正当......之时”。

【翻译】低廉的商品价格，国内旱灾和委内瑞拉的经济危机造成了古巴共产党政府的资金短缺，限制了其贸易的能力，恰恰在它可以充分利用与美国经济贸易开放的时候。

又如：

He jumped onto the bus just as it was pulling away.  正当公共汽车开动时他跳上了车。

He began to speak before everybody else, just as the meeting started. 刚一开会他就抢先发言。

He left home just as last spring began.  他离家出走刚好是去年春天开始的时候。

Just as I was busiest, he must come and ask me so many questions.  正当我忙得要命时，他却来问了我好些问题。