In South Carolina, local officials reported 300,000 had already evacuated the coast as of Wednesday.
Isaac is forecast to move across the central Lesser Antilles and into the eastern Caribbean Sea Thursday, and then move across the eastern and central Caribbean Sea through Saturday.
The government of France has issued a Hurricane Watch for Guadeloupe and Martinique.
Forecasters have warned that Storm Helene could pose a danger to life when it bears down on the United Kingdom and Republic of Ireland next week. This rainfall may cause risky flash flooding.
Rainfall amounts of 2 to 4 inches with isolated amounts up to 6 inches over elevated terrain are forecast across Martinique and Guadeloupe.
The storm is now around 530 miles southeast of Cape Fear, North Carolina, and is moving west-northwest at 17 mph. "Maximum sustained winds remain near 90 miles per hour (150 km/h) with higher gusts".
Tottenham Hotspur without Dele Alli and Hugo Lloris against Liverpool
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Given the lack of deep convection to sustain the cyclone, continual gradual weakening is expected.
On the forecast track, Isaac will move near or over the central Lesser Antilles on Thursday.
Of the Atlantic's two active hurricanes - Florence and Helene - Florence posed the greatest threat to land, as it neared the Carolinas and Virginia as a Category 3 hurricane.
Isaac was a hurricane Sunday night but downgraded when maximum sustained winds fell below 74 miles per hour.
The yellow warning is in place from 6pm on Monday until midday on Tuesday, with the impact limited to the south east of the province.
"Life-threatening, catastrophic flash flooding and significant river flooding is likely over portions of the Carolinas late this week into early next week, as Florence is expected to slow down as it approaches the coast and moves inland". Sustained winds slowed slightly to 125 miles per hour Tuesday afternoon, making it a Cat 3 storm.