Yes that is a big concern with furniture on a rooftop or for that matter anything that is not hefty in weight( hold comments please – i have been known to budge in minor hurricanes !!!! ) or tied down.
We recommend furniture that is of a decent weight, umbrellas need to be put down after every use – there is no room for Mary Poppins moments in Manhattan- unless you are on Broadway !
Furniture should be difficult for you to lift – if it is not then it will be an easy lift as mother nature huffs and puffs at your terrace – a good rule of thumb is the heavier it is for you to move then the harder it will be for the wind to do so.
If heavy wind is forecast it certainly can’t hurt to bring all occasional pillows and sofa cushions in from the terrace, lay over small occasional tables and take the glass off of any of your dining tables that may have it and lay it flat on the ground or store it in your apartment ( preferable )
If unsure please don’t hesitate to speak to your building Super or call us at Plant Specialists – we are happy to advise you