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MIAMI (CBSMiami) – Tropical Storm Isaac is poised to gain strength in the coming days.

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At 5 p.m. Isaac was located about 1390 miles east of the Windward Islands.

Isaac is moving toward the west near 12 mph and is expected to accelerate during the next 36 hours.

A westward motion is forecast to continue through the end of the week, with Isaac expected to move across the Lesser Antilles and into the eastern Caribbean Sea Wednesday night or Thursday.

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Maximum sustained winds have increased to near 70 mph with higher gusts.

Additional strengthening is forecast, and Isaac is expected to become a hurricane tonight.

Weakening is anticipated to begin by the middle of the week while Isaac approaches the Lesser Antilles.

Tropical-storm-force winds extend outward up to 45 miles from the center.

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There are currently no coastal watches or warnings in effect.