By Roberto Samora and Marcelo Teixeira
SAO PAULO, Sept 20 (Reuters) - A strong heat wave moving over most of Brazil this week, amid the last days of winter in the Southern Hemisphere, is raising concerns among farmers and agronomists about the health of the coffee fields in the world's largest producer and exporter.
Forecasters expect temperatures above 40 Celsius (104 Fahrenheit) in many coffee producing regions in Brazil this week, with no rains seen until at least the end of the month.
The extreme heat for this period of the year could negatively impact coffee fields that have had an early flowering, cutting the production potential for next year's crop, experts said.
"Arabica coffee trees are sensitive to temperatures above 33 Celsius during the reproductive phase," said agronomist Jonas Ferraresso, who advises coffee farms in Sao Paulo and Minas Gerais, the two largest producing states in Brazil.
He said that flowers could feel the heat and fail to develop into fruits.
Ferraresso and other agronomists, however, said that this is only the first occurrence of flowers in Brazil and that more important ones are expected around early October, if the rains return.
"There is always an impact from these conditions (dry, hot weather). But it is something that will take time to evaluate," said Jose Braz Matiello, a researcher at Brazil's agency Funcafe.
He said that the heat itself would not be such a big problem if rains return soon, but could be a bigger threat if the dry spell continues.
Grain producers in Brazil are also facing difficulties with the start of soy planting due to the weather.
Jim Roemer, publisher of the WeatherWealth newsletter at bestweatherinc.com, said that temperatures in some coffee areas in Brazil will be as much as 20 Fahrenheit higher than normal for this time.
"There is a bit of concern in the coffee market," he said.
(Reporting by Roberto Samora, in Sao Paulo, and Marcelo Teixeira, in New York; Editing by Sharon Singleton)
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