May weather isn’t as ‘merry’ as you think it is. Philly is getting one nasty nor’easter this weekend.

Thomas Dekker and the other poets through the ages who have rhapsodized about this “merry month” clearly never spent a May weekend at the Jersey Shore like the one the beach towns are experiencing.

A potent and glacially moving nor’easter is generating sand-shifting and wave-building onshore winds, along with occasionally heavy rains throughout the region. Rain could intrude into at least part of Mother’s Day, and in all likelihood this will be one of the coolest May weekends in the period of record.

The National Weather Service posted a wind advisory until Sunday morning for the entire region for gusts to 50 mph; a gust of 59 mph was recorded at Ocean City. By midmorning, PECO was reporting more than 10,000 outages. A general 1.5 to 2 inches of rain had been measured, and with another round of heavy rains, flood warnings were in effect for northern Montgomery and Upper Bucks Counties.

Widespread tidal flooding along the oceanfront, the back bays and the Delaware River was a near certainty. The Shore is under a flood warning from 11 p.m. Saturday until 7 a.m. Sunday with “moderate” flooding expected. A flood advisory was issued for Sunday morning for the tidal Delaware for Philly and Delaware and Lower Bucks Counties.

And the weather service said the siege of onshore winds could continue for days, forecasters said.

Rain postponed the Phillies-New York Mets game Friday night at Citizens Bank Park (no, it had nothing to do with the Thursday night meltdown in which the Phils blew a six-run lead in the ninth inning). And the forecast suggests that another postponement is likely Saturday.

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Said the weather service, “The weekend looks downright ugly overall.”

If this were closer to Groundhog Day than Mother’s Day, your local supermarkets might be mobbed. Cool high pressure, or heavier air, to the north will obstruct movement of a storm, with its lighter air, off the Virginia coast, a scenario common for major snowstorms.

“This would be quite the setup if it were a winter situation,” said Dave Dombek, a senior meteorologist with AccuWeather Inc., in State College.

Jonathan O’Brien, a meteorologist at the National Weather Service Office in Mount Holly, said this would be “a very classic nor’easter type of evolution,” and that his colleagues have mused over what might have shaken from the sky if this were February. “Believe me it’s come plenty of times the last couple of days,” he said.

Instead, the storm is expected to have wrung out up to 3 inches of plain old rain by the time it all ends.

Driven by the pressure differences between the high and the coastal storm, winds have intensified. They should back off some Sunday, but gusts to 25 mph inland and to 35 mph at the Shore are expected.

“And it’s going to be chilly,” Dombek added, “not just lah-de-dah cold.” Saturday and Sunday’s forecast highs, in the low to mid-50s, would be in the rarefied atmosphere for coolness around here. Saturday’s high would the lowest for a May 7 since 1967, when it didn’t get past 47 at Philadelphia International Airport, the record for the date. Sunday’s would be the lowest in 75 years.

That has everything to do with the Atlantic Ocean.

Not coincidentally, the sea-surface temperatures this week off the Atlantic City coast have been in the mid-50s, and the northeast winds are going to import the chilled overlying air.

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By contrast, the previous Thursday through Saturday the air was Arizona-dry as humidity dropped into the teens and fire alerts were issued, the result of persistent breezes from the west.

“Two completely different air masses, two completely different situations,” said Mike Silva, a meteorologist at the weather service office.

But this would hardly be the first time that winds from the east bore a change of fortune in May.

On that stormy May 7, 1967, the winds from the northeast howled up to 35 mph.

“The merry merry month of May,” in the enduring words of Elizabethan poet Thomas Dekker, isn’t all blooming azaleas, its reputation notwithstanding.

Based on 55 years of available data, among the months May ranked last in numbers of clear days. And for average numbers of days with measurable rainfall, it ranks just a few drops behind April — 11.1 vs. 11.3.

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“You’ve got that big pond out there, east of us,” said Dombek, “that can really play havoc with the weather east of the mountains.”

In this instance the beaches almost certainly are going to lose some sand, although at least the lunar cycle isn’t favorable for providing an astronomical tug to any flooding, said Dombek. However, the storm will be so slow to pull away, forecasters say, that the onshore winds could continue well into next week.

“It’s not in any hurry to get out of there,” Dombek said. In fact, he said, it’s possible that the storm will execute “some kind of weird loop-to-loop” and drift back to the coast.

As to whether the storm will honor the region’s mothers by at least shutting off the rain, “It’s a tough call,” O’Brien said. It will be drier and warmer the farther north and west you go.

But, “I wouldn’t put the expectations too high for Sunday,” he said.