By Phuong Nguyen and Mas Alina Arafin

HANOI/BANDAR LAMPUNG, Indonesia, Oct 31 (Reuters) - C offee plants in Vietnam were unaffected by Tropical Storm Trami that made brief landfall in central Vietnam even though heavy rain was recorded in the country's coffee-growing area, traders said on Thursday.

Farmers in the Central Highlands, Vietnam's largest coffee-growing region, sold beans for 108,200-108,600 dong ($4.28-$4.30), slightly down from last week's 109,000-110,000 dong.

Storm Trami made landfall in Vietnam last Sunday with downpours in the Central Highlands over two days but traders said it did not harm the crop.

"There was concern that rains may disrupt harvesting activities but farmers have just harvested around 5% of the crop so the impact is minor," said a trader based in the coffee belt.

"We still have to monitor the weather closely from now until Christmas," the trader said, adding that it had been sunny for the past two days.

Traders offered 5% black and broken-grade 2 robusta

at a discount range of $10-$30 per ton to the January contract.

"Prices will quickly adjust to the weather, especially when the Central Highlands is forecast to receive rains in the next three months," said Nguyen Ngoc Quynh, deputy chief of the Mercantile Exchange of Vietnam.

Traders expect coffee trading activities to peak from late November when supplies are built up.

According to Vietnam Coffee and Cocoa Association, the export value of the harvest in the previous crop season peaked at $5.4 billion, up 33% against the previous season even though the volume was down by 12.7%.

In Indonesia, Sumatran robusta beans were offered at $240-250 premium to the December contract, up from $200 premium last week.

Another trader said the premium to the January contract was unchanged at $200, as "there were no changes in the volume of green beans delivered".

($1 = 25,260.0000 dong)

(Reporting by Phuong Nguyen and Mas Alina Arifin; Editing by Nicholas Yong)

((phuong.nguyen@thomsonreuters.com; +84-24-3852-9623))