Tropical storm Ernesto has weakened slightly and is expected to begin moving over portions of the Windward Islands.

Ernesto's maximum sustained winds early Friday decreased to near 75 km/h with some strengthening forecast over the next two days.

A tropical storm warning is in effect for Dominica, St. Lucia and Martinique and Guadeloupe.

The storm is centred about 45 kilometres southeast of St. Lucia and 60 kilometres east-northeast of St. Vincent. It's moving west near 24 km/h.

Ernesto's current forecast track shows it possibly becoming a hurricane next week as it heads toward the Gulf of Mexico.