(CNN) — Hurricane Erin is rapidly intensifying as it tracks above the northeastern Caribbean Saturday, churning up rough surf and sending rain and gusty winds to islands south of its path.

Erin was a Category 4 hurricane with sustained winds near 155 mph as of late Saturday morning, according to the National Hurricane Center. The storm’s winds more than doubled in speed in 24 hours: Erin was a 70 mph tropical storm at 8 a.m. Friday.

Additional strengthening, powered up by the warmer than normal Atlantic, is expected Saturday afternoon. An increase in strength to a Category 5 is now forecast from the National Hurricane Center.

Fluctuations in intensity are expected for the rest of the weekend. By the middle of next week, Erin is forecast to at least double or triple in size, which will

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