A year after New York City's jubilant pride parade celebrated a high point for gay Americans with the nationwide legalization of same-sex marriage, the atmosphere surrounding the annual march couldn't be more different.

Sunday's parades in New York, San Francisco and other cities are unfolding two weeks after a gay nightclub in Florida became the site of the nation's deadliest mass shooting by a single gunman in modern U.S. history.

Celebrations planned around such themes as supporting transgender people and pressing for economic justice have quickly taken on new meanings. Parade-goers will see increased security, anti-violence messages and tributes to those killed in Orlando.

But organizers don't want the massacre to stamp out the defiant exuberance of events rooted in declaring that gay people aren't afraid to be seen and heard.

"Last year was such a celebratory time, and this year, we have this happening," says James Fallarino, a spokesman for organizers of the New York parade, one of the nation's oldest. "But that's also why it's so important that we are out and loud and proud.

"If we change our event — if we make everything somber — it's, in many ways, allowing those who wish to silence us to win."

Sunday's parades do have a new milestone to mark: President Barack Obama on Friday designated the site around New York City's Stonewall Inn as the first national monument to gay rights. A 1969 police raid on the bar helped catalyze the gay rights movement.

To be sure, the often raucous marches will be tempered with messages of respect and grief for the 49 people massacred and more than 50 wounded in Orlando.

In New York, the lead float will be dedicated to the victims. Marchers will carry 49 orange flags — the color of choice for campaigns against gun violence — through the route. A "We Are Orlando" solidarity group has been added to the lineup. And gun-control, anti-gun-violence groups have joined the lineup since the shooting forged new bonds between them and gay-rights activists.

"As the mom of a gay teen, Orlando terrified me," says Shannon Watts, the founder of Moms Demand Action for Gun Sense in America. She and 19-year-old daughter Emma, who is gay, plan to join about 200 other people behind the group's banner in the parade.

It's "such an important way for these two communities to come together," said Watts, whose group also has members joining other parades.

At San Francisco's parade, also among the country's oldest, a "We're Orlando" group of about 300 people will be fourth in the lineup. Victims will be honored with a moment of silence when the march reaches the grandstand. A memorial with their photos will be set up inside City Hall.

"It's been an interesting experience to build the parade with kind of a heavier message" after the optimistic sentiment last year, Stephanie Mufson said as she supervised assistants building floats Thursday for the event.

It's still unclear, and may always be, exactly what prompted gunman Omar Mateen's rampage. He pledged allegiance to the Islamic State group in a 911 call. His ex-wife said he was mentally ill. His father has suggested he was angry with gays.

Whatever the instigation, Mateen targeted a popular gay club, and pride celebrations around the country since have faced a sense of heightened risk. Police in the Los Angeles area arrested a heavily armed man who told officers he was headed to a big pride parade in West Hollywood. Houston police investigated a tweeted threat against their city's pride parade.

New York police plan to deploy roving counterterrorism units and use bomb-sniffing dogs, rooftop observation posts, police helicopters and thousands of officers to provide extra layers of security at Sunday's parade. Thousands of uniformed officers will line the route, supplemented by plainclothes officers in the crowd. While the city has provided similar protections in the past, "you'll see more" this year, Democratic Mayor Bill de Blasio said.

San Francisco spectators will face metal detectors, for the first time, and more police than usual will keep watch. Some participants aren't welcoming the stepped-up security: Two honorary grand marshals and a health clinic that serves sex workers withdrew Friday from the parade to protest the heavy police presence.

Chicago police have put 200 more officers than usual on duty for the city's pride parade Sunday. Organizers have nearly doubled their corps of private security agents, to 160.

For all the security and solemnity, some spectators at pride parades this month have made a point of making merry.

"We had fun. That is what gay people do," comedian Guy Branum wrote in a New York Times essay after attending the West Hollywood parade. "Our answer to loss and indignity, it seems, is to give a party, have a parade and celebrate bits of happiness."

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Associated Press writer Tom Hays in New York and AP video journalist Haven Daley in San Francisco contributed to this report.