“The major commodity exporters are the most vulnerable,” Smith, who founded Ecstrat, a London-based research firm, said by email today. “If, as I believe, the oil price is likely to remain at currently depressed levels or even move lower over the medium term, then the main Gulf currencies will come under increasing pressure, although there will be ferocious political resistance to any devaluation.”

Egypt has struggled with a foreign-currency shortage since the 2011 Arab Spring protests sent investors and tourists fleeing. It has attempted to fend off further weakness after this year's 8.6 percent slump in the pound by limiting access to hard currencies. Egyptian investors are restricted from obtaining foreign currency by buying shares locally and selling them abroad, for example. Egyptian central bank officials weren't available for comment.

Problems in Egypt, Nigeria, and Former Soviet States

Egypt has relied on aid from the Gulf states in recent years. Saudi Arabia, Qatar, and the United Arab Emirates probably will be “forced eventually to adjust or abandon their dollar pegs,” said Smith. “But any movement is unlikely over the short term.”

He recommends being “very underweight” in emerging-market stocks. The benchmark MSCI Emerging Markets Index, down 13 percent this year, will probably be down 20 percent by year-end, he said.

In Nigeria, trading restrictions imposed in February to prevent the flight of dollars have left importers unable to pay suppliers while the black market in foreign banknotes thrives. The naira had tumbled 20 percent in the 12 months to February.

Standard & Poor's said last month another naira devaluation is “inevitable”—possibly by more than 15 percent.

“We haven't seen any reason so far to institute a change in the FX policies,” Ugochukwu Okoroafor, a spokesman for the Central Bank of Nigeria, said by phone from Abuja today.

Former Soviet states that may struggle to withstand depreciation pressure include Armenia, Azerbaijan, and Georgia, according to Timothy Ash, a credit strategist for emerging markets at Nomura Holdings Inc. in London. Most have less ammunition than Kazakhstan, which has almost $100 billion in overall reserves.

To Per Hammarlund at SEB's chief emerging-market strategist in Stockholm, depreciations of 10 to 20 percent look likely for Kyrgyzstan, Turkmenistan, and Tajikistan.

“They simply don't have much of a choice but to follow Russia and emerging markets more generally,” Hammarlund said by email. He recommends selling developing-nation currencies while looking out for a “rebound and potential stabilization” after the first U.S. interest-rate increase.

Rand Also Vulnerable

Speculation of monetary policy tightening by the Federal Reserve has driven currencies lower in the past few months. Turkey's lira weakened beyond 3 per dollar for the first time today and Russia's ruble fell for a sixth day to a six-month low. Ukraine's currency dropped 3 percent, extending this year's biggest exchange-rate retreat after the Belarusian ruble.

Along with former Soviet countries, African currencies are vulnerable, including free-floating exchange rates that have already tumbled, like South Africa's rand, said Berg at SocGen. The rand's 11 percent retreat this year, to 12.9 per dollar, looks set to extend to 14 within two months, he said by email.

Reliance on China for exports makes the rand the “most vulnerable” in the region from Europe to Africa, according to Tatiana Orlova, the chief Russia economist for Royal Bank of Scotland Group Plc in London. Exports to China account for more than 12 percent of South African economic output, more than double the proportion for Kazakhstan, according to RBS.

–With assistance from Ahmed A. Namatalla in Cairo.

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