MONTEVIDEO -- Uruguay is holding a presidential runoff election Sunday that pits Sen. Jose "Pepe" Mujica, a former guerrila leader and candidate of the governing leftist Broad Front, against National Party candidate Luis Alberto Lacalle, who served as president from 1990 to 1995.

The polls opened at 8:00 a.m. amid a forecast that calls for heavy rains during the day.

The opening of the polls in provinces in central and northern Uruguay affected by flooding was delayed, election officials said.

Nine of Uruguay's 19 provinces - Artigas, Salto, Paysandu, Soriano, Cerro Largo, Treinta y Tres, Colonia, Rivera and Durazno - have been affected by flooding in the past week.

"There were some problems and delays" in opening rural election precincts in Salto, Paysandu, Treinta y Tres and Soriano, Electoral Court chief Edgardo Martinez Zimarioff said.

The polls are scheduled to close at 7:30 p.m., but election officials have the option of extending the balloting for up to one hour if voters are still on line at closing time.

Some 2.5 million people are eligible to vote in the runoff between the two top vote-getters in the Oct. 25 election.

Neither candidate won more than 50 percent of the vote last month, forcing Sunday's runoff.

Mujica garnered 48 percent of the vote in the first round, while Lacalle won 29 percent of the vote.

The Colorado Party, whose candidate won 18 percent of the vote in the election, is supporting Lacalle this time around.

The 74-year-old Mujica said as he cast his ballot in Montevideo that he was "thinking about some who are not here," referring to comrades who died in the armed struggle.

Mujica, former leader of the National Liberation Movement-Tupamaros, was cheered by hundreds of supporters as he cast his ballot.

The weather service is forecasting heavy rains, strong winds, thunderstorms and possible hail for Sunday afternoon.