Accepted answer

sorry for the late reply, your both problems are solved with some minor modification, for all the red points, you need to specify their color: 'red'like:

   x: 11,
   y: 99.20,
   color: 'red',
   extprop: 'flood'

and the other problem was due to specifying xaxis categories. so i put them outside and used the formatter to populate xaxis labels and also used tickinterval: 1

xaxis: {
        rotation: 90,
        align: "left",
        formatter: function () {
            return dates[this.value];
    tickinterval: 1

see the working demo here

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