(Updates prices; adds comment, NEW YORK dateline) NEW YORK/LONDON, Nov 21 (Reuters) - Cocoa prices rose on Tuesday, with an increase in grindings expected to diminish the size of any global surplus this season, while arabica coffee regained some ground after a recent slide. Volume was light ahead of the U.S. Thanksgiving holiday on Thursday.
* March New York cocoa settled up $21, or 1 percent, at $2,110 per tonne, trading within the prior session's range and buoyed by further evidence that grindings are increasing.
* Ivory Coast cocoa grinding was up 15 percent in October versus a year ago, data from the exporters' association GEPEX showed, following higher processing in Europe, Asia and North America.
* Rabobank forecast in its Outlook 2018 report global grindings will rise by 2.3 percent in 2017-18 after an increase of more than 4 percent in 2016-17.
* "This is rather optimistic, but processor margins remain very high, mainly due to the strength of the butter ratio," the bank said in a report on the outlook for 2018.
* Production in Ivory Coast is also expected to be significantly below last season's record.
* Rabobank forecast a global surplus of 130,000 tonnes in 2017-18, down from 300,000 tonnes the previous season. Its "very preliminary" forecast for 2018-19 was a surplus of 60,000 tonnes.
* March London cocoa settled up 9 pounds, or 0.6 percent, at 1,583 pounds per tonne. The discount of December under March <LCCZ7-H8> widened to 40 pounds, the biggest for the contract.
* March arabica coffee settled up 0.9 cent, or 0.7 percent, at $1.2665 per lb, after falling 3.4 percent the prior two sessions.
* Dealers said the potential for a record crop in Brazil next year could limit the scope of any price rebound while producer selling abated as they wait to see how well cherries set on coffee trees following unusually dry conditions.
* Rabobank forecast a global coffee surplus of 3 million bags in 2018/19, the vast majority in arabicas, compared with a deficit of 4.7 million bags in 2017/18.
* January robusta coffee settled down $9, or 0.5 percent, at $1,801 per tonne.
* March raw sugar settled down 0.1 cent, or 0.7 percent, at 14.88 cents per lb.
* Prices extended losses after data showed speculators had sharply reduced their net short position, causing the short-covering rally of the prior two weeks to abate, dealers said.
* March white sugar settled down $2.3, or 0.6 percent, at $386.50 per tonne.
(Reporting by Marcy Nicholson in New York and Nigel Hunt in London; editing by David Goodman and Susan Thomas)