SAO PAULO, Sept 18 (Reuters) - A weather forecaster said on Monday that dry weather this month could delay the start of soy planting in important producing areas of Brazil, a leading exporter of the commodity.

Marco Antonio dos Santos, founder of Rural Clima, wrote there is there is not enough soil humidity to start planting soybeans at this stage in states like Paraná, Mato Grosso and Mato Grosso do Sul.

"Rains are only expected to return next week and even so, they will be irregular," he said.

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Because Pacific Ocean waters are colder than usual - though not enough to confirm the La Niña phenomenon - there is a tendency that rainfall in key grain regions will begin later than in the last season, Santos said.

But he added that later planting of soy as well as corn does not mean there will be problems with the crops during the 2017/2018 season.

"Last year farmers planted soy ahead of schedule because of plentiful rain in September," said Eduardo Godoi, a soybean farmer in Mato Grosso.

Dry weather is hampering germination of soybean seeds in areas of Parana where some farmers began planting, according to Flávio Turra, a manager at cooperative group Ocepar.

For the next 10 days, dry and above-average temperatures are expected in most Brazilian soy producing areas, according to Somar Meteorologia, a weather service.

Yet Somar's more extended forecasts predict a return of rains to areas in Brazil's South, Southeast and Midwest starting at the end of September.

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By Oct. 2, there are models indicating rainfall between 15 and 30 millimeters, with some extremes of up to 50 millimeters, while other models indicate the possibility of rains between 5 and 15 millimeters, Somar said.

Traditionally, the rainy season occurs around the middle of October, and nothing in the models indicates anything unusual, Santos said in an interview last week. (Reporting by Roberto Samora and Ana Mano; Writing by Ana Mano; Editing by W Simon)