The 25-cent banana from a fruit-stand vendor has long been a New York tradition, as dependable as a Parthenon coffee cup from a diner. But last week New Yorkers who plunked down a quarter and headed on their way were in for a shock: Vendors asked for more.

Yesterday morning, one regular customer grabbed a banana at a fruit stand near City Hall. When he saw the price, 35 cents, freshly written on a cardboard sign, he muttered a disgruntled, “Why?” It’s a question the vendor, Ahmed Minhaj, has been getting many times a day – and one he wishes he could answer. All he knows is that last week, for the first time in nine years of selling fruit, the price of a box jumped from to $20 from $15, and he said he had no choice but to up the price.

Coming on the heels of last week’s record snowfall, the sudden price hike – up to as much as 40 cents a banana at some street vendors and 45 cents at some Midtown bodegas – triggered rumors that weather conditions had stopped the bananas.

Mother Nature is, indeed, to blame, but the source lies way beyond the city’s icy roadways. When hurricanes battered Central America last year, the bananas went with them. More recently deluges have washed away many banana fields in Ecuador, the South American nation where most of New York’s bananas come from. While the executive director of Ecuador’s association of banana exporters, Eduardo Ledesma, said in a phone interview from Quito that production is not down, the quantity reaching New York is.

“The glut we have seen in bananas for the past 10 years is probably drying up,” the northeast senior sales manager for Dole Fruit, Slater Wilson, said.

Low production is only part of the story. Last month the “banana war” between America and the European Union that has raged for more than a decade concluded, in theory. At the request of America, Europe changed a tariff and quota system to a tariff-only regime.That move has resulted in more bananas going to Europe, exacerbating the shortage in supply in places like New York.

“Basically, there’s just not enough fruit coming in,” Anthony Esposito, owner of Esposito and Sons, which supplies 800 supermarkets, bodegas, and vendors in New York, said. “We’re going down to the ports to pick up our fruit and our suppliers are just coming up short because they’re not getting enough fruits from Colombia and Ecuador.”

His price differential is even greater than Mr. Minhaj’s supplier: Banana boxes that his company once sold for $14 a box are now going for $20 to $21. Many of his customers are reporting to him they needed to increase the price, with some going all the way up to 99 cents a pound. While the city’s larger stores are generally keeping prices low because of their greater margin, with Whole Foods in Chelsea selling for 69 cents a pound and FreshDirect for 59 cents, the smaller retailers are getting hit hard. One of Mr. Esposito’s recipients, the Park Slope Co-op, issued a one-page statement to its customers about why they regretfully had to hike the price of bananas.

For the street vendor, that explanation is word of mouth, and it happens daily. Mr. Minhaj said his strategy, if customers start to walk away, assuming a quarter is still enough for a banana, is to “politely tell them that they raised the price.” Sometimes he does not catch them in time. Or, like the customer yesterday who asked why they undercut him, paying only 30 cents.

Even more than his customers, Mr. Minhaj is hoping the price will go down again soon.While bananas are still his most profitable item, the margins are slipping. But the importers and wholesalers seem to be at a loss about when the shortage will end. Some say a few weeks, some say longer.

The manager at Top Banana at Hunts Point, Derek Kuras, who said he has never seen the price so high, said it’s a simple question of supply and demand. “There’s no supplies over there,” he said. “They’ve been saying it’s going to be a while, but who knows?”