Storms in October and November are unusual in the Caribbean, but they happen. The DR1 Weather Forum is one of the best places to go for updates on how the storms could affect travel plans in the Dominican Republic. See the updates on Tomas as it makes its way south of the DR and is expected to swerve to the north into Haiti and on to the northwest of the DR.
http://www.dr1.com/forums/weather-beyond/102242-h-season-outlooks-2010-a-84.html#post913634