Portsmouth Weather OverviewScoresFors & AgainstsWeatherPhotos Average Temperature Jan 43 °F6 °C Feb 50 °F10 °C Mar 52 °F11 °C Apr 54 °F12 °C May 59 °F15 °C Jun 63 °F17 °C Jul 68 °F20 °C Aug 68 °F20 °C Sep 64 °F18 °C Oct 59 °F15 °C Nov 50 °F10 °C Dec 50 °F10 °C Humidity Jan 68% Feb 74% Mar 68% Apr 65% May 66% Jun 73% Jul 68% Aug 70% Sep 70% Oct 72% Nov 73% Dec 74% Rain Jan 21mm Feb 32mm Mar 34mm Apr 19mm May 25mm Jun 110mm Jul 31mm Aug 35mm Sep 59mm Oct 59mm Nov 65mm Dec 72mm Clouds Jan 65% Feb 66% Mar 71% Apr 67% May 63% Jun 65% Jul 58% Aug 57% Sep 60% Oct 85% Nov 80% Dec 71% Air quality US AQI Jan 42 Feb 50 Mar 46 Apr 51 May 53 Jun 41 Jul 30 Aug 27 Sep 25 Oct 32 Nov 39 Dec 38 Sun Jan 1UVI Feb 2UVI Mar 2UVI Apr 3UVI May 4UVI Jun 5UVI Jul 6UVI Aug 5UVI Sep 4UVI Oct 2UVI Nov 1UVI Dec 1UVI