This summer has been an especially dangerous one for swimmers along New Jersey's coastline, with at least 10 drownings reported so far this year — and at least half of them blamed on rip currents.

The figures provided on Friday by the National Weather Service office in Mount Holly put New Jersey on pace to equal or exceed its worst rip-current fatality season.

"This data goes back to 1998," said Mitchell Gaines, a meteorologist at the Mount Holly office. "The only year with more rip-current deaths than we've had so far was back in 2008, when there were six deaths."​

Typically, said Gaines, the agency expects one to three rip-current deaths a year in New Jersey and Delaware. The most recent spike was in 2012, when five swimmers drowned off New Jersey as rip currents hauled them rapidly out to sea.

Among the latest victims was Pennsylvania banking executive Brian Zwaan of Berwyn, who was believed to be body-surfing off the Sea Isle City shoreline on Monday when he suffered neck and head injuries and drowned.

So far this summer, the Associated Press reported, rip currents have killed at least 40 swimmers along U.S. beaches, with Florida recording 11 deaths, the most of any state.

There have been 10 drownings reported so far this summer in New Jersey. Officials say the cause can be difficult to pin down, given that lifeguards and other witnesses aren't always present. Swimming after hours, when beach patrols have gone home for the night, is often associated with drowning deaths.

The grim drowning count began early this season, as authorities recorded two pairs of deaths.

In Atlantic City on June 15, 15-year-old Ramon Quinn died trying to rescue his friend Kaliyah Hand, 16. Both were caught in a rip current and went under. Hand's body was found the following Monday, washed ashore on a stretch of Margate beach. Quinn's body was found a week after the pair died along the beach in Atlantic City, according to police.

The day after Hand's and Quinn's deaths, two cousins drowned in Belmar, with no lifeguards present. On June 16, Mitzi Hernandez Nicolas, 13, and Emily Gonzalez Perez, 12, were swept out to sea by a rip current, according to the weather service. Both were from Belmar.

On July 16, a 12-year-old Elizabeth girl, Bianca Palma, was pulled from the surf in Sandy Hook and died the next day. According to the weather service, rip currents were to blame.

Only half of the deaths in the waters along the New Jersey coastline can be attributed to rip currents.

On June 25, the body of a 24-year-old Egyptian boardwalk worker, Ismail Ahmed Abdelmonem Ismail, was found washed up onshore in North Wildwood. He was identified by fingerprint analysis, according to police. He had gone swimming at night when lifeguards weren't around.

Another boardwalk worker, Zuzana Oravcova, 24, of Slovakia, went swimming early July 30 in Point Pleasant, with no lifeguards present. Her body was found the next day, eight miles south in Toms River. The weather service cited high surf as the cause of death.

The most recent death was that of a 74-year-old man in Sea Isle City on Wednesday. The man, not yet publicly unidentified, was knocked off his feet by a large wave and remained underwater. According to Sea Isle City police, fellow swimmers assisted the beach patrol in locating him. He was pulled onto dry land, where lifeguards administered CPR, along with police officers, before he was transported by helicopter to Atlantic City Medical Center. He died early the next morning.

The day before, Jeffrey Wilkens, 31, of Illinois, disappeared while swimming after sunset in Atlantic City. His body was found two days later, 10 blocks south of where he was swimming. Pedestrians noticed his body floating in the water near the former Revel casino and alerted police.

Zwaan, 58, died while swimming off Sea Isle City. One of his daughters said it was likely her father was body surfing, an activity he frequently enjoyed. Sea Isle City police said an autopsy indicated Zwaan's death was the result of "head and neck injuries complicated by drowning."

One witness on the beach that afternoon said he saw other beachgoers pull Zwaan from the water and lifeguards try to revive him using CPR. Police said he was pronounced dead two hours later.

Another beachgoer at Sea Isle City that day said the conditions of the sea floor in the area where people were swimming weren't good for bodysurfing. The man, a Wildwood lifeguard in the 1970s who asked that his name not be used, believes one of the safety issues is beach replenishment. He said the sand dredging doesn't smooth out the slope of the beach to the water's edge, instead leaving a steep drop-off that is apparent during low tide but unseen and underwater at high tide.

"What happens is, at the high-tide mark, the ocean drops very quickly into the water," said the former lifeguard. "So if you're out to your chest and you ride the wave 30 feet, you're going from six-feet-deep water into one-inch water before you can get off that wave. So it's causing the wave riders to ride the waves in and smack into the sand wall at the high tide."

The drop-off effect is well-known. A 2013 article in Scientific American gave a spotlight to a group of researchers in Delaware studying the issue.

The dangers of rip currents caught national attention on July 11, when a family in Panama City Beach, Fla. was caught up in the swift waters of the Gulf of Mexico. About 70 other beachgoers formed a human chain, linking arms to reach the swimmers in distress. The rescue mission took about an hour, according to one woman who helped, but everyone arrived safely on dry land to the sound of clapping and cheers.

Staff writer Joseph A. Gambardello contributed to this article.