The center of Tropical Storm Isaac, the ninth named storm of the 2012 hurricane season, was moving west-northwestward and was south-southwest of Puerto Rico late Thursday afternoon and was expected to approach Florida's southwestern coast by Monday morning, the National Hurricane Center (NHC) said.

NHC's five-day forecast cone predicts the center of the storm reaching the eastern Gulf of Mexico (GOM) west of Tampa, FL, by Tuesday morning. A hurricane warning was in effect for Haiti and portions of the Dominican Republic's southern coast, while tropical storm warnings and watches had been posted across the region, including the British Virgin Islands, Puerto Rico and portions of Cuba and the Bahamas.

Isaac had maximum sustained winds of 40 mph, and the storm was expected to strengthen through Saturday, possibly becoming a hurricane as it approaches the Dominican Republic and Haiti on Friday, NHC said.

There were no reports of GOM evacuations or shut ins, but Royal Dutch Shell plc and other companies said they were monitoring Isaac's progress. "We will continue to closely monitor weather reports and are preparing to take actions if necessary to respond accordingly," a Shell spokesman said.

Isaac has so far had "almost no impact at all" on natural gas futures prices, according to one New York floor trader (see related story).

Among the events potentially threatened by Isaac is the Republican National Convention, which is scheduled to be held in Tampa Aug. 27-30.

Farther out in the Atlantic, Joyce was upgraded to a tropical storm Thursday but was "no immediate threat to land," and was "losing organization, NHC said. Tropical Storm Joyce, which had maximum sustained winds of 40 mph, was 1,280 miles east of the Leeward Islands and was moving west-northwest at 14 mph. Little chance of strengthening was expected, and the forecast track of the storm was expected to keep it well away from the North American mainland.

The 2012 Atlantic hurricane season, which has so far been relatively mild, may be about to intensify, forecasters at Weather Services International (WSI) said this week (see Daily GPI, Aug. 22). WSI, the National Oceanic and Atmospheric Administration and forecasters at Colorado State University have recently nudged their tropical storm forecasters slightly higher from their original forecasts (see Daily GPI, Aug. 10; Aug. 7).

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