* Nikkei on track to post biggest weekly gain since Dec 2009 * Nikkei 15,000 in sight next week - broker By Ayai Tomisawa TOKYO, May 10 (Reuters) - The Nikkei share average surged to a 5-1/2 year high on Friday as the U.S. dollar broke above the elusive 100-yen mark and extended its gains, with exporters leading the charge as the Japanese currency's new lows looks set to further boost corporate earnings. The market is up 6.5 percent so far this week, on track for its biggest weekly gain since December 2009. "There is strong demand for currency-sensitive exporters today... even stronger than recent days," said a fund manager at a U.S. asset management firm. "Short-term investors are the main buyers, while long-term investors have yet to catch up with the steep rises recently. When they start buying aggressively, these exporters will likely rise further." The Nikkei jumped 2.8 percent to 14,581.95 by the midday break after hitting 14,630.47, the highest since January 2008 and surpassed the Nikkei 225 May options' settlement price at 14,601.95. Exporters took the spotlight, with Toyota Motor Corp rising 4.3 percent, Honda Motor Co advancing 2.7 percent and Komatsu Ltd gaining 4.4 percent. The Topix gained 2.2 percent to 1,207.41. WEAK YEN TREND SUGGESTS MORE UPSIDE IN STOCKS During Asian trade, the yen fell to as low as 101.20 per dollar, the lowest level in over four and a half years. The market was already upbeat after the dollar punched through 100 yen on Thursday, helped by data showing U.S. claims for unemployment benefits fell to the lowest level since January 2008. The yen's break below the key level was also underscored with data showing Japanese investors finally reversed their relentless net selling of foreign bonds. Japanese investors bought 309.9 billion yen ($3.1 billion) in foreign bonds in the week through May 4 after purchasing 204.4 billion yen in the prior week, according to the Ministry of Finance. "We've started seeing a new outlook for the Japanese market," said Kyoya Okazawa, head of global equities at BNP Paribas, adding that the yen's weakness has increased the likelihood of the Nikkei touching 15,000 as soon as next week. "Investors, who once snapped up asset-related shares, are selling them to buy more exporters, and more and more long-only investors will buy exporters," Okazawa said. With the earnings season in full swing and companies reporting strong results for the year ended March 2013, many of the blue chip companies have surprised investors with overly conservative forecasts for the current fiscal year. The likes of Toyota and Sony Corp based their foreign exchange assumptions at 90 yen to the dollar. However, traders were optimistic about the outlook for corporate Japan. "Conservative forecasts did not lead to pessimism in the market. They rather made us think, 'oh, they can generate such profits even at 90 yen, then their actual profits will be way better at the end of the day,'" said Takuya Takahashi, an analyst at Daiwa Securities. Bucking strength, Takeda Pharmaceutical Co Ltd tumbled 6.6 percent after the drugmaker cut its operating profit forecast for the year through March by 38 percent to 140 billion yen ($1.4 billion), citing competition from low-cost generic drugs.