BUENOS AIRES Argentina's monthly inflation is forecast to have hit 11.5% in September, according to the median of a Reuters poll of 20 analysts, remaining in the double digits though moderating slightly from its worst rate in 32 years last month.

The consumer price index (CPI) rose 12.4% in August, while annual inflation topped 124% in the month.

"September marks the second consecutive month with double-digit inflation," said Eugenio Mari, chief economist at the Libertad y Progreso Foundation.

The retail price index soared in August after the government devalued the local currency by almost 18% to 350 pesos, alongside a series of other economic measures ahead of the presidential elections on Oct. 22, analysts said.

"We estimate that inflation will sustain this dynamic for the coming months, without returning to a monthly rate of 10% until the end of the year," said Paula Gandara, an analyst at Adcap Asset Management.

The projections among the analysts surveyed ranged from a minimum rise of 10.7% to a maximum of 13.8% for September.

The Secretariat of Economic Policy recently began publishing a weekly measure of inflation in which it shows that in the week of Sept. 25 prices rose 1.3%, down from the 4.8% peak registered in mid-August.

"Although inflation remains at very high levels, it has slowed significantly," the Economy Ministry said.

However, economist Martin Kalos estimated that September's inflation figure "is similar to that of August. There's not going to be a slowdown."

He added that the Secretariat's newly launched weekly memo "is the only way it has to reach the elections and can show a slowdown," given that the final official data before the national vote is unlikely to show an improvement in inflation.

The official statistics institute INDEC will publish September's inflation data on Thursday at 1900 GMT, while the central bank will release its Market Expectations Survey (REM) shortly after.

It is likely to also vote on whether to hold the interest rate.

(Reporting by Walter Bianchi and Jorge Otaola; editing by Jonathan Oatis)