(Adds details, comments, tabular data, byline) By Saqib Iqbal Ahmed NEW YORK, Nov 27 (Reuters) - Speculators' net short dollar bets rose in the latest week after seven straight weeks of declines, according to calculations by Reuters and Commodity Futures Trading Commission data released on Monday. The value of the net short dollar positions, derived from net positions of International Monetary Market speculators in the yen, euro, British pound, Swiss franc and Canadian and Australian dollars, was $3.15 billion, in the week to Nov. 21. That compares with a net short position of $643 million the previous week and marks the 19th straight week that speculators have had a net short position on the greenback. To be short a currency means traders believe it will fall in value. In a wider measure of dollar positioning that includes net contracts on the New Zealand dollar, Mexican peso, Brazilian real and Russian ruble, the U.S. dollar posted a net short position valued at $5.23 billion, up from $2.41 billion a week earlier. "That's pretty consistent with the movement that we have been seen in the dollar. It has been trending weaker for pretty much most of the month of November," Sireen Harajli, FX strategist at Mizuho in New York. "There is a lot of uncertainty surrounding tax legislation and the way forward," she said. On Monday, President Donald Trump summoned Senate Republican tax writers to the White House to urge passage of a sweeping tax bill that congressional fiscal analysts said separately would balloon the federal budget deficit by $1.4 trillion over a decade. Investors are focused on lawmakers' efforts to overhaul the U.S. tax code and are closely tracking developments around the tax bill. Worries about potential delays in the implementation of tax cuts and the possibility of proposals being weakened have weighed on the dollar. The dollar index, which measures the greenback against six rival currencies, has slipped 1.7 percent so far in November. A Dec. 8 deadline for extending government funding is also raising concerns about a possible government shutdown, Harajli said. Meanwhile, the net short position on the Swiss franc was at 29,740 contracts, the largest since June 2012, the data showed. The Swiss National Bank has been selling francs for foreign currency in vast amounts for years to keep a lid on the soaring currency, whose rise has spelt danger for Switzerland's export-reliant economy. "It's very difficult to go long a currency if you don't think there is true upside," Harajli said. Japanese Yen (Contracts of 12,500,000 yen) $13.631 billion 24 Nov 2017 Prior week week Long 44,382 49,347 Short 166,984 185,346 Net -122,602 -135,999 EURO (Contracts of 125,000 euros) $-14.002 billion 24 Nov 2017 Prior week week Long 195,909 200,023 Short 100,472 115,437 Net 95,437 84,586 POUND STERLING (Contracts of 62,500 pounds sterling) $0.025 billion 24 Nov 2017 Prior week week Long 58,358 53,147 Short 58,658 57,680 Net -300 -4,533 SWISS FRANC (Contracts of 125,000 Swiss francs) $3.75 billion 24 Nov 2017 Prior week week Long 20,821 19,470 Short 50,561 47,453 Net -29,740 -27,983 CANADIAN DOLLAR (Contracts of 100,000 Canadian dollars) $-3.532 billion 24 Nov 2017 Prior week week Long 67,324 70,473 Short 22,199 23,138 Net 45,125 47,335 AUSTRALIAN DOLLAR (Contracts of 100,000 Aussie dollars) $-3.017 billion 24 Nov 2017 Prior week week Long 78,134 73,155 Short 38,317 29,123 Net 39,817 44,032 MEXICAN PESO (Contracts of 500,000 pesos) $-2.141 billion 24 Nov 2017 Prior week week Long 110,044 92,961 Short 29,658 30,428 Net 80,386 62,533 NEW ZEALAND DOLLAR (Contracts of 100,000 New Zealand dollars) $0.915 billion 24 Nov 2017 Prior week week Long 22,489 18,146 Short 35,883 30,037 Net -13,394 -11,891 (Reporting by Saqib Iqbal Ahmed; Editing by Tom Brown and Grant McCool)
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