You can only do that with bracket notation, which means you have to attach the variables to something.
The global scope would be window, so that would be window['hello' + newCount]
, but polluting the global namespace with a bunch of random properties doesn't sound like a good idea, so using an object seems better
var vars = {};
var newCount = parseInt($('#hello').html(), 10);
$('.hello').click(function(){
newCount++;
vars['hello' + newCount] = '<p>Hello World</p>';
});
alert( vars['hello1'] );