— On Day 1 of their tempest-tossed convention, Republicans ran up the debt, said a prayer — and walked away.

The Monday session, condensed to just seven minutes to keep people out of Tropical Storm Isaac’s way, was to have two purposes, according to the official Republican National Committee schedule: “Call to Order” and “Start Debt Clocks.”

RNC Chairman Reince Priebus did as advertised, hammering the convention to order with six strikes of his oversized gavel. With the first strike, the “Debt From Convention Start” number jumped right to $450; by the time Priebus left the stage, it was already up to $8.5 billion.

Priebus told the few delegates in attendance that the clock was intended to illustrate President Obama’s fiscal recklessness. He evidently didn’t consider that leaving the debt clock running and walking out might also highlight Republicans’ complicity.

But that is the least of Republicans’ troubles this week. They are at the mercy of Mother Nature, and it turns out she has a wicked sense of humor.

Over the weekend, when the forecasting models showed Isaac making a beeline for Tampa Bay, Republicans delayed most of their proceedings until Tuesday. As soon as Republicans postponed their event, Isaac changed course away from Tampa and toward New Orleans, where it is forecast to hit with hurricane-force winds at about the time Republicans begin their prime-time proceedings on Tuesday night.

At best, this weak rerun of Katrina will cause a split-screen effect in coverage of the convention; a groggy Anderson Cooper was spotted leaving his Tampa hotel Monday morning for storm-coverage duty in New Orleans. At worst, the juxtaposition of storm damage and balloon drops will make the Republicans appear insensitive.

Completing the cosmic joke, the weather would have been fine for a convention in Tampa on Monday: gusty, with intermittent showers and sun. But minutes before the 2 p.m. start of the abbreviated session at the Tampa Bay Times Forum, the wind and rain picked up and the National Weather Service issued a tornado warning for Tampa’s Hillsborough County. By the time the brief session ended, the sun had returned.

If there is any good to come out of this soggy spectacle, it will be that it hastens the demise of the political convention, which has become a meaningless anachronism. The Democrats’ convention next week has already been shortened to three days, and Republicans are joining Democrats in concluding that the drawn-out affairs of years past have become pointless.

“I’m not sure that having a four-day convention, for the future, makes a lot of sense,” House Speaker John A. Boehner (R-Ohio) told The Post’s Karen Tumulty and other reporters at a Monday lunch organized by the Christian Science Monitor. He said it may not be “worth the tremendous resources that are put into it.”

Tampa makes that case powerfully. Many city blocks have been converted to an armed encampment, and major roads have been shut down. Vans with mirrored walls and ceilings whisk participants to and fro within the security “perimeter.” Media organizations have erected elaborate sets and hospitality areas. In the hall, robotic cameras swing from the ceiling, where netted balloons are set for the inevitable, clichéd drop. Yet for all the elaborate preparation and expense, the televisions playing all around the convention showed little but Isaac’s red, yellow and green precipitation bands.

The RNC’s Priebus contributed to the irrelevance with his seven-minute show on Monday. He took the stage to tepid applause from a sparse crowd. “Wow!” he said.

“It is my privilege to proclaim the 2012 Republican National Convention in session and called to order,” Priebus informed them, smiling self-consciously and reading from one of those teleprompters Republicans often mock Obama for using. He continued: “The chair announces, pursuant to Clause 12, Paren B, Paren 1 of Rule 1 of the rules of the House of Representatives, the 2012 Republican National Convention stands in recess subject to a call of the chair.”

Priebus hammered his gavel again, grinned and flashed a mocking two thumbs up toward the crowd, equally divided between delegates and media representatives. “All right,” Priebus said. “So we’re in recess.” He then explained the debt clock, brought out a preacher and played a video of Mitt Romney making a patriotic speech, which thinned the crowd.

Priebus and the minister, Russell Levenson, offered thoughts for storm victims. The chairman thanked emergency workers helping “those in the path of Hurricane Isaac,” and the minister offered a prayer for “those already affected by the hurricane and those in its path.”

Amen. But if Isaac puts an end to political conventions, nobody should mourn.