Humidity

I’m not sure, but I think the 3.8 inches of rain that fell Sunday set a record for the date. Saturday had merely 1.24 inches while today was a practically Atacama-like .5 inches. With this rainfall, we’ve already eclipsed the 30-year average rainfall for August (6.3 inches so far compared with a 6.1 monthly average). The forecast discussion attributed this outpouring to a stalled weather front with sub-tropical connections. Basically instead of passing over like usual, a band of rain got hung up over Southeast and just kept gifting us with moisture.

In the big picture, such rainy weather is not that unusual (we do live in a rain forest, after all). What seemed a little less typical was just how warm it stayed. My sense* is that often when we have such rains this time of year, the temperatures will be in the upper 50s. To me, that feels relatively warm, but not particularly muggy. This event has seen lows around 58 or 59, with highs in the lower 60s.

Yesterday, when I was walking around the park, it started feeling kind of oppressive. I was beginning to break a pretty good sweat just walking back from the park. It did not feel hot, exactly, just quite muggy. I checked the current weather conditions and saw that the temperature was 64F with 93% relative humidity for a dew point of 62F. Some years ago I was told by someone who had grown up in the Southeast United States that the dew point was a better measure than straight temperature of how unpleasant the heat was. He told me that dew points over 60 were when it started to get uncomfortable. It’s hard to be sure, but my guess is that it’s pretty rare for this to occur around Sitka (mostly because it’s only rarely much warmer than the lower 60s – and those days tend to be drier).

It was interesting to observe (what I presume were) effects of these conditions. Most immediate was my own perception and physical response (it felt muggy and I started sweating noticeably even though I wasn’t doing anything strenuous). More interesting was the layer of fog forming and drifting across the water. As I walked out on the tide flats, I could see fog in the cove between the park and Canon Island. I didn’t realize at first it was dissipating, but after a few minutes it was pretty much gone. Upon rounding the corner to where the river was running through its channel in the estuary, I found much heavier fog (though it did not extend more than 15-20 feet above the ground). It was mostly limited directly above the river, and my guess is the relatively cool river water was sufficient to drop the air temperature down below the (relatively high) dew point, creating and maintaining the persistent fog layer (shown in photo at top).

* Maybe I can go back and check some weather records to verify this.